- Palladium-Copper-exchanged Y Type Zeolites: A True Heterogeneous Wacker Catalyst
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Evidence is presented that faujasite-type zeolites with specific Si:Al framework ratios exchanged with Pd(NH3)42+ and Cu2+, catalyse the oxidation of ethylene into acetaldehyde, in exactly the same way as the homogeneous Wacker system II and CuII in concentrated chloride solution>; the active centre is found to be a partially ammoniated PdII ion, most probably PdII(NH3)2, which itself belongs to an electron transfer chain consisting of the alkene reagent, the faujasite encaged PdII/Pd0 and CuII/CuI redox couples and dioxygen.
- Espeel, P. H.,Tielen, M. C.,Jacobs, P. A.
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- Catalytic dehydration of lactic acid to acrylic acid over dibarium pyrophosphate
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Barium phosphate catalysts were prepared by a precipitation method. The catalysts were calcined at 500 C for 6 h in air atmosphere and characterized by SEM for morphological features, by XRD for crystal phases, by N2 sorption for specific surface area, by TPD-NH3 for acidity and by TG for thermal stability. The dibarium pyrophosphate catalyst was found to have the best catalytic performance, ascribing to weak acidity on the surface. Under the optimal reaction conditions, 99.7% of the lactic acid conversion and 76.0% of the selectivity to acrylic acid were achieved over the dibarium pyrophosphate catalyst.
- Tang, Congming,Peng, Jiansheng,Fan, Guoce,Li, Xinli,Pu, Xiaoli,Bai, Wei
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- Mechanism of uncatalyzed and osmium(VIII) catalyzed oxidation of L-alanine by Copper(III) periodate complex in aqueous alkaline medium
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The kinetics of oxidation of the L-alanine (L-ala) by diperiodatocuprate(III) (DPC) was carried both in the absence and presence of osmium(VIII) catalyst in alkalinemedium at constant ionic strength of 0.01 mol dm-3 spectrophotometrically.The involvement of free radicals was observed in both the reactions. The oxidation products in both the cases were acetaldehyde and Cu(II), identified by spot test and spectroscopic studies. The stoichiometry is the same in both cases; that is, [L-ala]:[DPC] = 1:2. The reaction was first order in [DPC] and has negative fractional order in [OH-] in both the catalyzed and uncatalyzed cases. The order in [osmium(VIII)] was unity. A mechanism involving the formation of a complex between L-ala and DPC in case of uncatalyzed reaction and a mechanism involving the formation of a complex between L-alanine and osmium(VIII) in case of catalyzed reaction were proposed. The reaction constants involved in the different steps of the mechanisms were calculated for both reactions. The catalytic constant (Kc) was also calculated for catalyzed reaction at different temperatures. The activation parameters with respect to slow step of themechanisms were computed and discussed for both the cases. The thermodynamic quantities were also determined for uncatalyzed and catalyzed reactions. Copyright Taylor & Francis Group, LLC.
- Lamani, Shekappa D.,Veeresh, Tegginamat M.,Nandibewoor, Sharanappa T.
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- Photochemical redox reactions of copper(II)-alanine complexes in aqueous solutions
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The photochemical redox reactions of Cu(II)/alanine complexes have been studied in deaerated solutions over an extensive range of pH, Cu(II) concentration, and alanine concentration. Under irradiation, the ligand-to-metal charge transfer results in the reduction of Cu(II) to Cu(I) and the concomitant oxidation of alanine, which produces ammonia and acetaldehyde. Molar absorptivities and quantum yields of photoproducts for Cu(II)/alanine complexes at 313 nm are characterized mainly with the equilibrium Cu(II) speciation where the presence of simultaneously existing Cu(II) species is taken into account. By applying regression analysis, individual Cu(I) quantum yields are determined to be 0.094 ± 0.014 for the 1:1 complex (CuL) and 0.064 ± 0.012 for the 1:2 complex (CuL2). Individual quantum yields of ammonia are 0.055 ± 0.007 for CuL and 0.036 ± 0.005 for CuL2. Individual quantum yields of acetaldehyde are 0.030 ± 0.007 for CuL and 0.024 ± 0.007 for CuL2. CuL always has larger quantum yields than CuL2, which can be attributed to the Cu(II) stabilizing effect of the second ligand. For both CuL and CuL2, the individual quantum yields of Cu(I), ammonia, and acetaldehyde are in the ratio of 1.8:1:0.7. A reaction mechanism for the formation of the observed photoproducts is proposed.
- Lin, Chen-Jui,Hsu, Chao-Sheng,Wang, Po-Yen,Lin, Yi-Liang,Lo, Yu-Shiu,Wu, Chien-Hou
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- Kinetics and Thermochemistry of the CH3CO Radical: Study of the CH3CO + HBr --> CH3CHO + Br Reaction
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The kinetics of the reaction between CH3CO and HBr has been studied using a heatable tubular reactor coupled to a photoionization mass spectrometer.CH3CO was produced homogeneously by laser photolysis in the presence and absence of HBr.Radical decays were monitored in time-resolved experiments.Rate constants were determined at five temperatures in the range 300-400 K and fitted to the Arrhenius expression, 6.4 (+/-3.6) * 10-13 exp-1/RT> cm3 molecule-1 s-1.This kinetic information was combined with known rate constants andArrhenius parameters for the reverse reaction to obtain the heat of formation of CH3CO.Both second law and third law procedures were used to obtain this thermochemical information from these rate constants.The two determinations of this heat of formation were in close agreement (differing by only 0.4 kJ mol-1).These results, taken together, provide a CH3CO heat of formation of -10.0 +/- 1.2 kJ mol-1 at 298 K which is 14 kJ mol-1 higher than the value in common use.The current results imply a CH3-CO bond enthalpy of 45.1 (+/-1.5) kJ mol-1 which is 14 kJ mol-1 lower than currently believed and a CH3CO-H bond enthalpy of 373.8 (+/-1.5) kJ mol-1 which is higher by this same figure.Former disparities between reported CH3CO heats of formation associated with the equilibrium systems studied to obtain this thermochemical information are resolved.
- Niiranen, Jukka T.,Gutman, David,Krasnoperov, Lev N.
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- Kinetic evidence for an anion binding pocket in the active site of nitronate monooxygenase
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A series of monovalent, inorganic anions and aliphatic aldehydes were tested as inhibitors for Hansenula mrakii and Neurospora crassa nitronate monooxygenase, formerly known as 2-nitropropane dioxygenase, to investigate the structural features that contri
- Francis, Kevin,Gadda, Giovanni
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- Catalytic power of pyruvate decarboxylase. Rate-limiting events and microscopic rate constants from primary carbon and secondary hydrogen isotope effects
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Isotope effects ([rate constant for light isotopic substrate]/[rate constant for heavy isotopic substrate]) for the action of the thiamin diphosphate dependent pyruvate decarboxylase of Saccharomyces carlsbergensis (EC 4.1.1.1) on pyruvate, pyruvate-1-13C, pyruvate-2-13C, and pyruvate-3-d3 have been determined for each of the steady-state kinetic parameters k/A (second-order in pyruvate), k/B (first-order in pyruvate), and k (zero-order in pyruvate). The 1-13C effects are 1.008 ± 0.010 (k/A), 1.013 ± 0.024 (k/B), and 1.024 ± 0.006 (k). The 2-13C effects are 1.013 ± 0.009 (k/A), 0.951 ± 0.020 (k/B), and 1.039 ± 0.004 (k). The 3-d3 effects are 0.883 ± 0.013 (k/A), 0.881 ± 0.026 (k/B), and 1.057 ± 0.005 (k). Effects with 2-oxobutanoate and 2-oxobutanoate-3-d2 are 0.951 ± 0.012 (k/A), 0.821 ± 0.096 (k/B), and 1.057 ± 0.005 (k). Pyruvate decarboxylase was already known to be hysteretically activated by the substrate, with pyruvate binding to the regulatory site with dissociation constant 8 mM and producing unimolecular activation (0.46 s-1) and deactivation (0.033 s-1). The isotope effects lead to rate constants for substrate binding to the catalytic site of 8.2 × 104 M-1 s-1, for substrate departure from the catalytic site of 120 s-1, for decarboxylation of 640 s-1, and for product release of 640 s-1. Pyruvate decarboxylase increases the rate of decarboxylation of pyruvate by thiamin alone by a factor of 3 × 1012 at pH 6.2, 30°C. Under these conditions, conversion of activated enzyme and pyruvate to the enzymic species preceding decarboxylation is 4 × 1012 times faster than the specific-base-catalyzed addition of thiamin to pyruvate. The enzymic species preceding decarboxylation reverts to activated enzyme and free pyruvate 6 × 109 times faster than the specific-base-catalyzed reversion of the adduct of thiamin and pyruvate to thiamin and free pyruvate. Enzymic decarboxylation is 107 times faster than decarboxylation of the adduct of thiamin and pyruvate.
- Alvarez, Francisco J.,Ermer, Joachim,Hübner, Gerhard,Schellenberger, Alfred,Schowen, Richard L.
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- Kinetics of acid-catalyzed hydration of acetylene. Evidence for the presence in the solution phase of unsubstituted vinyl cation
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The rates of acetylene hydration in the convenient range of aqueous sulfuric acid (and those of propyne, tert-butylacetylene, ethylene, propene, and tert-butylethylene, for comparative purposes) have been measured at 25 °C with an NMR technique. The correlation of the kinetic data with the excess acidity function X gives a value of 1.12 for the slope parameter m*, which suggests that the intermediate is protonated acetylene, C2H3+ (probably as vinyl cation 3 rather than as hydrogen-bridged ion 4). The comparison with the m* value for the hydration of ethylene (1.50) indicates that protonated acetylene possesses stronger susceptibility to solvation than ethylium ion C2H5+. The deuteration patterns in the products (acetaldehyde and crotonaldehyde) obtained in deuteriosulfuric acid rule out the reversibility of the protonation process and also the conversion between 3 and 4.
- Lucchini, Vittorio,Modena, Giorgio
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- Reaction of Catalase with Ethylhydrogen Peroxide
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C2H5OOH reacts with catalase in a basically irreversible reaction in the course of which the species called compound (I) is formed and decomposed.The formation of compound (I) is preceded by the formation of a precursor complex which is able to react with a further molecule of C2H5OOH to yield an inactive biperoxy complex.The biperoxy complex causes a diminution of the extent of formation of compound (I) at high .As a consequence, compound (I) can never be formed quantitatively.Some of its physical constants can, nevertheless, be evaluated.Compound (I) with C2H5OOH appears to retrain C2H5OH in its structure.
- Kremer, Mordechai L.
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- Highly efficient catalyst for the decarbonylation of lactic acid to acetaldehyde
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The gas phase decarbonylation of lactic acid was performed over various silica-supported heteropolyacids. The obtained performances were, by far, higher than those previously described in the literature. In particular, the best results were obtained for silicotungstic acid-based catalysts, which showed very high yields of acetaldehyde (81-83%) at high lactic acid conversion (up to 91%). The Royal Society of Chemistry 2010.
- Katryniok, Benjamin,Paul, Sebastien,Dumeignil, Franck
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- Single-turnover studies on brewer's yeast pyruvate decarboxylase: C(2)-proton transfer from thiamin diphosphate
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Rate constants for formation of acetaldehyde from pyruvate catalyzed by the thiamin diphosphate (TDP)-dependent enzyme pyruvate decarboxylase (PDC; EC 4.1.1.1) from Saccharomyces carlsbergensis were determined under single-turnover conditions at 30°C in 100 mM sodium 2-(N-morpholino)ethanesulfonate buffer (pH 6.00) containing 100 mM pyruvamide, 10 mM MgSO4, and 12.5 μM sodium pyruvate. Observed rate constants in the range kobsd = 2.5-6.7 s-1 for 33-104 μM (8-15 mg mL-1) pyruvamide-activated PDC agree with values of kobsd calculated by numerical integration with microscopic rate constants derived previously from steady-state kinetic isotope effects. The observed rate constant kobsd = 6.7 ± 0.4 s-1 is independent of the concentration of pyruvamide-activated PDC in the range 104-150 μM. The decrease in the concentration dependence of the observed rate constants at > 104 μM PDC is consistent with either a change in rate-limiting step or complex formation involving the reactants. There is little or no primary kinetic isotope effect, (kH/kD)obsd ≤ 1.2, for C(2)-hydron exchange from PDC-bound TDP for 33-104 μM pyruvamide-activated PDC. This provides evidence against rate-limiting C(2)-proton transfer between C(2)-H in PDC-bound TDP and a catalytic base with -7 ≤ ΔpKa (= pKaBH - pKaC(2)H) ≤ 7 to form a discrete ylide intermediate during catalysis by PDC.
- Crane III, Edward J.,Vaccaro, Joseph A.,Washabaugh, Michael W.
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- Unimolecular Decomposition of Pyruvic Acid: An Experimental and Theoretical Study
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The thermal decompostion of pyruvic acid diluted in Ar has been studied behind reflected shock waves over the temperature range 850-1000 K, with a total density range of (0.3-1.3) x 10-5 mol/cm3.The decomposition process was monitored by time-resolved IR emission from carbon dioxide product.The vacuum-UV absorption at 193 nm suggested the production of hydroxyethylidene from the initial decomposition.This carbene isomerizes to acetaldehyde at temperatures higher than those used under the present conditions.From the experimental results, we propose that the initial reaction occurs through a five-center transition state (TS) as CH3COCOOH -> CH3COH + CO2 with a rate constant k = 1012.46exp(-40.0 kcal mol-1/RT) s-1.An ab initio molecular orbital calculation at the HF/6-31G**//HF/3-21G level shows that the energy of the five-center TS producing hydroxyethylidene is lower by 60 kcal/mol than that of the four-center TS leading directly to acetaldehyde.A theoretically evaluated rate constant agrees with the experimental value, in support of the proposition that the reaction path occurs through the five-center TS to produce the carbene radical.Also, it appears that the carbene subsequently isomerizes through two routes leading to acetaldehyde and/or vinyl alcohol.
- Saito, Ko,Sasaki, Goki,Okada, Kazumasa,Tanaka, Seiji
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- Ammonia promoted barium sulfate catalyst for dehydration of lactic acid to acrylic acid
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The dehydration of lactic acid (LA) to acrylic acid over ammonia promoted barium sulfate was studied under various conditions. Interplanar spacing (d) calculated from the enlarged (121) diffraction peak of XRD patterns with the Bragg equation is influenced by preparation conditions, which determines the acid-base properties of the prepared barium sulfate. The present work focused on the preparation conditions such as alkaline agents, pH values and calcination temperatures, which affected the d value. It was found that aqueous ammonia was used as an alkaline agent at pH = 5 to synthesize barium sulfate with an appropriate d value, which displayed an excellent catalytic performance for LA dehydration to acrylic acid. In the presence of the prepared barium sulfate with an appropriate d value, the dehydration reaction of lactic acid proceeded efficiently, with 100% lactic acid conversion and ~82% acrylic acid selectivity. The unprecedented catalytic performance is due to a balance between acidic sites and basic sites existing on the surface of the prepared catalyst. The catalyst is very stable for at least 24 h. The deactivation catalyst can be easily regenerated as it is calcined at 500 °C for 10 h under the air atmosphere.
- Li, Xinli,Chen, Zhi,Cao, Ping,Pu, Wenjie,Zou, Weixin,Tang, Congming,Dong, Lin
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- The Dehydrogenation of Ethanol in Dilute Aqueous Solution Photosensitised by Benzophenones
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The photochemical properties of a series of water-soluble benzophenones have been evaluated in dilute aqueous solution.The compounds possess lowest-energy singlet and triplet excited states demonstrating considerable n,?* character.As such, irradiation of the compounds in aqueous solution containing ethanol (2percent v/v) results in pinacol formation via a triplet-state hydrogen-abstraction process.In the presence of a colloidal Pt catalyst, the intermediate ketyl and 1-hydroxyethyl radicals can be used to reduce water to H2.The rate of H2 formation and its total yield depend upon the nature of the substituent used to solubilise the benzophenone.The rate at which the ketyl radical transfers an electron to the Pt particles can be rationalised in terms of thermodynamic and electrostatic factors.
- Green, Peter,Green, William A.,Harriman, Anthony,Richoux, Marie-Claude,Neta, Pedatsur
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- Oxidation of threonylmethionine by peroxynitrite. Quantification of the one-electron transfer pathway by comparison to one-electron photooxidation
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Peroxynitrite can modify methionine by one- and two-electron oxidation pathways. Here, we have quantified the extent of one-electron oxidation of threonylmethionine (Thr-Met) by peroxynitrite using a characteristic reaction according to which Thr-Met sulfur radical cations decompose via fragmentation of the Thr side chain, yielding acetaldehyde. The efficiencies, f(acet, photo) for the formation of acetaldehyde from Thr-Met sulfur radical cations were obtained by means of one-electron photooxidation using triplet 4- carboxybenzophenone. Exact quantum yields for the formation of Thr-Met sulfur radical cations by triplet 4-carboxybenzophenone were obtained by laser flash photolysis and time-resolved UV spectroscopy. Acetaldehyde yields were measured for the reaction of peroxynitrite with Thr-Met, and division of these acetaldehyde yields by f(acet, photo) yielded the extents to which peroxynitrite reacted with Thr-Met via the one-electron transfer pathway. There was little one-electron oxidation of Thr-Met by peroxynitrite at pH 7.4, i.e., 1.5%, 1.8%, and 5.3% based on the total chemical conversion of Thr-Met for Thr-Met concentrations of 1 x 10-3, 5 x 10-4, and 1.75 x 10- 4 M, respectively. In all cases the major reaction product was the two- electron oxidation product threonylmethionine sulfoxide. However, at pH 6.0, one-electron oxidation of Thr-Met showed a significantly higher efficiency of 14% for [Thr-Met] = 1.75 x 10-4 M. Under all experimental conditions the extent of one-electron oxidation increased with decreasing peptide concentration in agreement with a recently established mechanism according to which the one-electron oxidation of Met by peroxynitrite requires a unimolecular transformation of peroxynitrous acid to an excited species which is the ultimate one-electron oxidant.
- Jensen, Jana L.,Miller, Brian L.,Zhang, Xiaoping,Hug, Gordon L.,Sch?neich, Christian
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- 4,5-Dihydro-1,2,3-oxadiazole: A Very Elusive Key Intermediate in Various Important Chemical Transformations
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4,5-Dihydro-1,2,3-oxadiazoles are postulated to be key intermediates in the industrial synthesis of ketones from alkenes, in the alkylation of DNA in vivo, and in the decomposition of N-nitrosoureas; they are also a subject of great interest for theoretical chemists. In the presented report, the formation of 4,5-dihydro-1,2,3-oxadiazole and the subsequent decay into secondary products have been studied by NMR monitoring analysis. The elusive properties evading characterization have now been confirmed by 1H, 13C, and 15N NMR spectroscopy, and relevant 2D experiments at very low temperatures. Our experiments with suitably substituted N-nitrosoureas using thallium(I) alkoxides as bases under apolar conditions answer important questions on the existence and the secondary products of 4,5-dihydro-1,2,3-oxadiazole. Short-lived! 4,5-Dihydro-1,2,3-oxadiazole is generated by treatment of N-(2-chloroethyl)-N-nitrosourea with thallium alkoxides at low temperatures, but it is not formed by nucleophilic dealkylation of the corresponding N-methyloxadiazolinium salt. Even at -90 °C, 4,5-dihydro-1,2,3-oxadiazole cannot be detected directly. However, it was identified by analysis of its decay products, acetaldehyde, ethylene oxide, and diazomethane (see scheme).
- Banert, Klaus,Singh, Neeraj,Fiedler, Benjamin,Friedrich, Joachim,Korb, Marcus,Lang, Heinrich
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- Zur Acetalbildung aus Alkoholen und Acetylen mit Platin- und Palladiumverbindungen als Katalysator
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The platinum and palladium catalyzed addition of alcohols to acetylene to give acetals was investigated.The catalytic activity and productivity in dependence on the platinum compound and alcohol used, on the oxidation state of platinum and the cocatalytic effect of HCl are discussed.Systems of the type X2/HX (X = ClO4-, BF4-) are introduced as the first catalytically active palladium-containing systems.
- Steinborn, Dirk,Nuenthel, Ralph,Krause, Katrin
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- Kinetic Studies of Secondary Alcohol Photo-oxidation on ZnO and TiO2 at 348 K Studied by Gas-chromatographic Analysis
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Kinetics of conversion of propan-2-ol and butan-2-ol to the corresponding ketones by photoassisted dehydrogenation, (-H2)*, to lower aldehydes by a photoassisted Cα-Cβ bond cleavage process, (α-β)*, and to trace quantities of alkene by photoassisted dehydration (-H2O)* have been investigated at oxygen partial pressures in the range 0-700 Torr and at alcohol partial pressures of 0-60 Torr, utilising dynamic flow photoreactors and gas-chromatographic analysis.Qualitatively similar results were obtained either with a 'continuous reactant flow plus continuous u.v. illumination' procedure allied to intermittent sampling, or with a 'pulsed reactant and analysis' procedure.Both procedures yielded dependence upon alcohol pressure indicative of two parallel photoassisted pathways to (-H2)* product, one being Langmuir-Hinshelwood (LH*) and the other Eley-Rideal (ER*) in character.A decline in activity of the metal oxide surfaces as photoassisted conversion of alcohol increased was observed with both procedures and affected the LH* process for (-H2)* more strongly.It is proposed that this LH* process involved alcohol chemisorption and hole localisation at coordinatively unsaturated O2-cus ions.The ER* process is envisaged to have involved encounter of alcohol (from the gas phase or from a reversibly adsorbed weakly bound state) with a much more numerous type of surface location capable of being photoactivated by hole capture.The proposed mechanisms account for observed dependences of the (-H2)* process upon square root of the incident light intensity, upon alcohol pressure and upon oxygen pressure.
- Cunningham, Joseph,Hodnett, Benjamin K.
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- Highly selective production of hydrogen peroxide on graphitic carbon nitride (g-C3N4) photocatalyst activated by visible light
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Photocatalytic production of hydrogen peroxide (H2O2) on semiconductor catalysts with alcohol as a hydrogen source and molecular oxygen (O2) as an oxygen source is a potential method for safe H 2O2 synthesis because the reaction can be carried out without the use of explosive H2/O2 mixed gases. Early reported photocatalytic systems, however, produce H2O2 with significantly low selectivity (~1%). We found that visible light irradiation (λ > 420 nm) of graphitic carbon nitride (g-C 3N4), a polymeric semiconductor, in an alcohol/water mixture with O2 efficiently produces H2O2 with very high selectivity (~90%). Raman spectroscopy and electron spin resonance analysis revealed that the high H2O2 selectivity is due to the efficient formation of 1,4-endoperoxide species on the g-C 3N4 surface. This suppresses one-electron reduction of O2 (superoxide radical formation), resulting in selective promotion of two-electron reduction of O2 (H2O2 formation).
- Shiraishi, Yasuhiro,Kanazawa, Shunsuke,Sugano, Yoshitsune,Tsukamoto, Daijiro,Sakamoto, Hirokatsu,Ichikawa, Satoshi,Hirai, Takayuki
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- The 4-Oxalocrotonate Tautomerase- and YwhB-Catalyzed Hydration of 3E-Haloacrylates: Implications for the Evolution of New Enzymatic Activities
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4-Oxalocrotonate tautomerase (4-OT) catalyzes the conversion of 2-oxo-4E-hexenedioate to 2-oxo-3E-hexenedioate through the intermediate, 2-hydroxy-2,4E-hexadienedioate. 4-OT and a homologue found in Bacillus subtilis (designated YwhB) share sequence identity and two key catalytic groups, Pro-1 and Arg-11, with the two subunits comprising trans-3-chloroacrylic acid dehalogenase (CaaD). 4-OT and YwhB have now been found to display a low-level hydratase activity, resulting in the dehalogenation of 3E-haloacrylates. The enzymes are highly selective for the (E)-isomer, and Pro-1 is critical for the activity while an arginine is likely required. Two mechanisms are proposed in which Pro-1 functions as a general base or a general acid catalyst and, along with the arginine, facilitates the Michael addition of water. Both mechanisms suggest an intriguing route for the evolution of the CaaD activity. One or more mutations could decrease the hydrophobic environment of the active site, which would make it more favorable for a hydrolytic reaction, thereby raising the pKa of Pro-1 and increasing the concentration of enzyme in the reactive form. Copyright
- Wang, Susan C.,Johnson Jr., William H.,Whitman, Christian P.
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- Catalytic oxidation of ethyl acetate over LaBO3 (B = Co, Mn, Ni, Fe) perovskites supported silver catalysts
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A series of silver catalysts supported on lanthanum based perovskites LaBO3 (B = Co, Mn, Ni, Fe) were synthesized and evaluated in the catalytic oxidation of ethyl acetate. XRD, BET, TEM/HRTEM, HAADF-STEM, XPS and H2-TPR were conducted, and the results indicate that redox activity of the catalysts is of great importance to the oxidation reaction. Activity tests demonstrated that Ag/LaCoO3 was more active than the other samples in ethyl acetate oxidation. Moreover, the CO2 selectivity, COx yields and byproduct distributions for all catalysts were studied, and Ag/LaCoO3 showed the best catalytic performance. Besides, Ag/LaCoO3 also showed excellent catalytic activity for other OVOCs.
- Qin, Yu,Shen, Fangxia,Zhu, Tianle,Hong, Wei,Liu, Xiaolong
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- Linkage of catalysis and regulation in enzyme action. Carbon isotope effects, solvent isotope effects, and proton inventories for the unregulated pyruvate decarboxylase of Zymomonas mobilis
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The pyruvate decarboxylase of the bacterium Zymomonas mobilis (ZMPDC), in contrast to that of yeast (SCPDC), is not regulated by substrate and shows simple Michaelis-Menten kinetics with rate constants k/B (equivalent to kcat/Km) and k (equivalent to kcat). C1-carbon-13 isotope effects obtained by direct measurement with 99% 13C-labeled substrate, which permits determination of the isotope effect on both k/B and k, give 13(klB) = 1.010 ± 0.008 and 13k = 1.019 ± 0.008. These are similar to the effects with SCPDC and show that decarboxylation is about 20% rate-limiting at low pyruvate levels and about 40% rate-limiting at high pyruvate levels. From these values, the rate constants for individual events in the catalytic cycle can be estimated (to within about a factor of 2) for ZMPDC: addition of pyruvate to the enzyme, 8 × 105 M-1 s-1; off-reaction of pyruvate, 300 s-1; decarboxylation, 1200 s-1; product release, 750 s-1. Solvent isotope effects are small and normal (k/B[HOH]/k/B[DOD] = 1.25 ± 0.05, k[HOH]/ k[DOD] = 1.30 ± 0.01), in strong contrast to those for SCPDC (e.g., an inverse isotope effect of 2 on k/B), which were considered to arise from sulfhydryl-addition reactions coupled to regulation. The proton inventories for ZMPDC are also quite different from those for SCPDC. The overall picture suggests that ZMPDC possesses a similar chemical mechanism but somewhat greater catalytic power than SCPDC because of both stronger uniform binding of all states and greater specific stabilization of transition states relative to reactant states. Thus introduction of the regulatory features of SCPDC is coincident with a reduction in catalytic power.
- Sun, Shaoxian,Duggleby, Ronald G.,Schowen, Richard L.
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- Rhodium-Iodide Catalyzed Carbonylation of Methyl Formate into Acetaldehyde or Methyl Acetate: Mechanistic Aspects
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Under CO pressure, the rhodium/ionic-iodide system catalyzes either the reductive carbonylation of methyl formate into acetaldehyde or its homologation into methyl acetate. The influence of the reaction conditions on the selectivity of these two reactions was investigated and it was found that the former occurs selectively only in N-methylpyrrolidone (NMP) (or related solvents), for low I-/Rh ratio, low substrate concentration, and high CO pressure, whereas methyl acetate is preferentially formed, in the same solvent, at higher I- and substrate concentrations and under lower CO pressure. By using labeled methyl formate (H13CO2CH3) it was also shown that the carbonyl group of acetaldehyde or methyl acetate does not result from that of methyl formate. In situ IR studies conducted under catalytic conditions (high-pressure, high-temperature) have not enabled the identification of any other catalytic species than RhI2(CO)-2 (which is also the active species in methanol or methyl acetate carbonylations), whatever the reaction conditions ([I-], PCO . . .). Plausible mechanisms are proposed for these reactions in which the essential role played by NMP in controlling the CH3I content in the reaction medium is clarified and taking into account these experimental data.
- Fontaine, Marc,Castanet, Yves,Mortreux, Andre,Petit, Francis
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- Catalytic dehydration of lactic acid to acrylic acid using calcium hydroxyapatite catalysts
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A series of calcium hydroxyapatite (HAP) catalysts were synthesised with a Ca/P ratio ranging from 1.3 to 1.89 by a co-precipitation method that involved changing the pH of the calcium and phosphorous precursors. The physicochemical characterization by XRD, SEM, BET surface area and CO2 and NH 3-TPD techniques confirmed the hydroxyapatite formation. These HAP catalysts were used for the vapour phase dehydration of lactic acid to acrylic acid. The HAP catalyst with a Ca/P ratio of 1.3 was found to be the most efficient catalyst among the synthesised series, which gave 100% conversion of lactic acid and 60% selectivity towards acrylic acid at 375 °C when a 50% (w/w) aqueous solution of lactic acid was used. The higher selectivity towards acrylic acid has been correlated to the increased acidity and reduced basicity of the HAP catalyst with a Ca/P ratio of 1.3 compared to the other HAP catalysts. The catalyst was found to be very stable and no deactivation was observed even after 300 h of reaction time. In situ FTIR studies were performed for understanding the mechanistic aspects and showed the formation of calcium lactate as an intermediate species during the dehydration of lactic acid to acrylic acid.
- Ghantani, Vidhya C.,Lomate, Samadhan T.,Dongare, Mohan K.,Umbarkar, Shubhangi B.
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- Ethanol steam reforming over Rh and Pt catalysts: Effect of temperature and catalyst deactivation
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In this study 0.2% Rh/alumina and 0.2% Pt/alumina catalysts were tested for ethanol steam reforming (ESR) over a range of temperatures (773-873 K) at 20 barg with a 5:1 steam to ethanol ratio. Hydrogen was always the main product over Rh/Al2O3 although liquid products such as acetaldehyde, diethyl ether and acetone were also produced (2O3 also produced hydrogen as the main product but at 773 K significant levels of ethene were formed. Less liquid product was formed over the Pt/Al2O3 (-1) however the platinum catalyst gave a low activation energy more typical of a diffusion controlled system (~20 kJ mol-1). At 873 K the platinum catalyst is more active (90% conversion cf. ~60%) and gives a higher hydrogen selectivity (55% cf. 49%) than the rhodium catalyst. Temperature-programmed oxidation (TPO), Raman spectroscopy, BET and SEM analysis were used to characterise the nature of the coke species for reactions at 773 K, 823 K and 873 K. The TPO results indicated that different types of coke were deposited on both catalysts during ESR. Carbon nanotubes and filamentous coke were observed on the catalysts after ESR at 873 K. Raman analysis revealed that the coke deposited on the catalysts was graphitic in nature and the disorder in the graphitic type coke generally increased with an increase in the reaction temperature.
- Bilal, Muhammad,Jackson, S. David
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- Identification of a hypothetical protein from podospora anserina as a nitroalkane oxidase
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The flavoprotein nitroalkane oxidase (NAO) from Fusarium oxysporum catalyzes the oxidation of primary and secondary nitroalkanes to their respective aldehydes and ketones. Structurally, the enzyme is a member of the acyl-CoA dehydrogenase superfamily. To date no enzymes other than that from F. oxysporum have been annotated as NAOs. To identify additional potential NAOs, the available database was searched for enzymes in which the active site residues Asp402, Arg409, and Ser276 were conserved. Of the several fungal enzymes identified in this fashion, PODANSg2158 from Podospora anserina was selected for expression and characterization. The recombinant enzyme is a flavoprotein with activity on nitroalkanes comparable to the F. oxysporum NAO, although the substrate specificity is somewhat different. Asp399, Arg406, and Ser273 in PODANSg2158 correspond to the active site triad in F. oxysporum NAO. The kcat/KM-pH profile with nitroethane shows a pK a of 5.9 that is assigned to Asp399 as the active site base. Mutation of Asp399 to asparagine decreases the kcat/KM value for nitroethane over 2 orders of magnitude. The R406K and S373A mutations decrease this kinetic parameter by 64- and 3-fold, respectively. The structure of PODANSg2158 has been determined at a resolution of 2.0 A, confirming its identification as an NAO.
- Tormos, Jose R.,Taylor, Alexander B.,Daubner, S. Colette,Hart, P. John,Fitzpatrick, Paul F.
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- Formation of Acetaldehyde from L-Ascorbic Acid and Related Compounds in Various Oxidation Systems
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The quantities of acetaldehyde formed from L-ascorbic acid, L-threonic acid, and D-erythrose upon oxidation with Fenton's reagent and upon UV irradiation were determined by gas chromatography.When 10 μmol of L-ascorbic acid was oxidized with Fenton's reagent, 316 nmol of acetaldehyde was recovered.When 10 μmol of L-ascorbic acid was irradiated (λ=300 nm) for 12 h, 297 nmol of acetaldehyde was produced.Upon oxidation with Fenton's reagent, L-threonic acid (10 μmol) and D-erythrose (10 μmol) produced 112 and 81.5 nmol of acetaldehyde, respectively.Acetaldehyde was formed from D-erythrose but not from L-threonic acid by photolysis, suggesting that acetaldehyde formation involved a Norrish type II reaction.Acetaldehyde was also formed from aqueous solutions of L-asorbic acid (122 nmol/10μmol), D-erythrose (37.0 nmol/10μmol), or L-threonic acid (27.9 nmol)/10μmol) with the presence of Fe2+ at 37 deg C under an air stream.This study is the first to report formation of acetaldehyde from ascorbic acid. Keywords: Antioxidant; acetaldehyde; ascorbic acid; low-density lipoprotein
- Miyake, Takashi,Shibamoto, Takayuki
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- Effect of ascorbic acid and its derivatives on the radiation-induced transformations of oxygenated ethanol and its aqueous solutions
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Upon irradiation ascorbic acid and 5,6-O-isopropylidene-2,3-O-dimethylascorbic acid are capable of lowering the yields of the main products of γ-radiolysis of oxygen-saturated ethanol or its aqueous solutions at pH 7 by virtue of reduction of peroxyl radi
- Brinkevich
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- Generation, Microwave Spectrum, andAb InitioMO Calculation oftrans-1-Nitrosopropene, CH3CHCH - NO (synform)
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trans-1-Nitrosopropene (synform) was generated in the gas phase by pyrolysis of 1-chloro-1-methyl-2-(hydroxyimino)ethane and identified by microwave spectroscopy. The microwave spectrum of the pyrolysate was observed in the frequency range from 8.0 to 40.
- Sakaizumi, Takeshi,Tanaka, Hideki,Hirano, Kouji,Kuze, Nobuhiko,Ohashi, Osamu
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- Formation of CH3CHO in the Combination of CH3 with CHO
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By reacting atomic hydrogen with mixtures of CH3Br and CO to generate CH3 and CHO radicals simultaneously, the formation of CH3CHO by combination of CH3 with CHO has been observed.For experiments at 473K, it is shown that the rate coefficient for this reaction is twice the product of the square roots of those for mutual termination of CH3 and CHO, to within the error limits.With this approximation, a model reaction scheme has been developed to analyse the effects of varying the pressures of CH3Br and CO; thereby the yields of CH3CHO produced by the combination of CHO with CH3 have been derived in the temperature range 373-473K, with a total pressure of 600 Torr.The yield appears to decrease slightly with increasing temperature, falling from ca. 0.55 at 373K to ca. 0.42 at 473K.The competing reaction generates CH4 plus CO, and it is argued that the two reactions proceed through different transition states.By computer simulation, it is shown that deviations from the model at lower temperatures are due to participation of CH3CO.
- Callear, Anthony B.,Cooper, Ian A.
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- Efficient and selective conversion of lactic acid into acetaldehyde using a mesoporous aluminum phosphate catalyst
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Although acetaldehyde is a very important compound and has been utilized as a useful synthon for various important chemicals, it has been synthesized in industry through a petroleum route until now. Herein, we have successfully developed a sustainable route using a heterogeneous catalyst. In the presence of mesoporous aluminum phosphate (MAP3), the decarbonylation reaction of lactic acid proceeded efficiently, with 100% lactic acid conversion and ~92% acetaldehyde selectivity. The catalyst shows high stability for at least 248 h. The unprecedented catalytic performance is due to rich medium acidic sites existing on the catalyst surface. This journal is
- Tang, Congming,Peng, Jiansheng,Li, Xinli,Zhai, Zhanjie,Bai, Wei,Jiang, Ning,Gao, Hejun,Liao, Yunwen
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- Ethanol Steam Reforming by Ni Catalysts for H2 Production: Evaluation of Gd Effect in CeO2 Support
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Abstract: Ni-based catalysts supported on CeO2 doped with Gd were prepared in this work to investigate the role of gadolinium on ethanol conversion, H2 selectivity, and carbon formation on ethanol steam reforming reaction. For this, catalysts containing 5 wt% of Ni impregnated on supports of ceria modified with different amounts of Gd (1, 5, and 10 wt%) were used. Ex-situ studies of XRPD suggest an increase of the lattice parameters, indicating a solid solution formation between Gd and Ce. Results of TPR showed an increase in metal-support interactions as the content of Gd increased. In situ XRPD studies indicated the formation of a GdNiO ternary phase for the catalysts containing Gd, which is in agreement with the results obtained by XANES. The catalysts were tested at three temperatures: 400?°C, 500?°C, and 600?°C. The conversion and productivity showed dependence with the Gd content and also with the temperature of the reaction. After the catalytic tests, catalysts containing Gd presented filamentous carbon possible due to a change in the reaction pathway. The highest ethanol conversion and H2 productivity were obtained at 600?°C for all catalysts and the best catalyst at this temperature was 5Ni_5GdCeO2. The promising performance of this catalyst may be associate with the lowest formation of GdNiO ternary phase, among the catalysts containing Gd, which means more Ni0 active species available to convert ethanol. Graphical Abstract: [Figure not available: see fulltext.]
- Assaf, Elisabete M.,Ferreira, Gabriella R.,Lucrédio, Alessandra F.,Nogueira, Francisco G. E.
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- Binary Au–Cu Reaction Sites Decorated ZnO for Selective Methane Oxidation to C1 Oxygenates with Nearly 100% Selectivity at Room Temperature
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Direct and efficient oxidation of methane to methanol and the related liquid oxygenates provides a promising pathway for sustainable chemical industry, while still remaining an ongoing challenge owing to the dilemma between methane activation and overoxidation. Here, ZnO with highly dispersed dual Au and Cu species as cocatalysts enables efficient and selective photocatalytic conversion of methane to methanol and one-carbon (C1) oxygenates using O2 as the oxidant operated at ambient temperature. The optimized AuCu–ZnO photocatalyst achieves up to 11225 μmol·g–1·h–1 of primary products (CH3OH and CH3OOH) and HCHO with a nearly 100% selectivity, resulting in a 14.1% apparent quantum yield at 365 nm, much higher than the previous best photocatalysts reported for methane conversion to oxygenates. In situ EPR and XPS disclose that Cu species serve as photoinduced electron mediators to promote O2 activation to ?OOH, and simultaneously that Au is an efficient hole acceptor to enhance H2O oxidation to ?OH, thus synergistically promoting charge separation and methane transformation. This work highlights the significances of co-modification with suitable dual cocatalysts on simultaneous regulation of activity and selectivity.
- Gong, Zhuyu,Liu, Huifen,Luo, Lei,Ma, Jiani,Tang, Junwang,Xing, Jialiang,Xu, Youxun
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supporting information
p. 740 - 750
(2022/01/03)
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- Photophysics of Perylene Diimide Dianions and Their Application in Photoredox Catalysis
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The two-electron reduced forms of perylene diimides (PDIs) are luminescent closed-shell species whose photochemical properties seem underexplored. Our proof-of-concept study demonstrates that straightforward (single) excitation of PDI dianions with green
- Li, Han,Wenger, Oliver S.
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supporting information
(2021/12/23)
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- Catalytic Oxidation of Ethylene in Solutions of Palladium(II) Cationic Complexes in Binary and Ternary Aqueous Organic Solvents
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Abstract: The effect of organic solvents on the rate of ethylene oxidation with p-benzoquinone to acetaldehyde in aqueous organic solutions of palladium cationic complexes has been studied. It was found that the reaction rate increased when the acceptor number of the solvent increased and the donor number decreased. The oxidation of ethylene and cyclohexene in binary (N-methylpyrrolidone–H2O) and ternary (acetonitrile–N-methylpyrrolidone–H2O) solvents was studied in more detail. In contrast to the acetonitrile–Н2О system, in the N-methylpyrrolidone–Н2О binary solvent hydrogen peroxide oxidizes ethylene to acetaldehyde in the presence of Pd(II) cationic complexes. The use of a solvent N-methylpyrrolidone acceptable for cyclohexene (CH) oxidation technology leads to a decrease in the rate and selectivity of cyclohexanone synthesis.
- Oshanina, I. V.,Pestunova, U. V.,Podtyagina, A. V.,Rusnak, I. N.,Temkin, O. N.
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p. 734 - 743
(2022/01/13)
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- Dual utility of a single diphosphine-ruthenium complex: A precursor for new complexes and, a pre-catalyst for transfer-hydrogenation and Oppenauer oxidation
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The diphosphine-ruthenium complex, [Ru(dppbz)(CO)2Cl2] (dppbz = 1,2-bis(diphenylphosphino)benzene), where the two carbonyls are mutually cis and the two chlorides are trans, has been found to serve as an efficient precursor for the synthesis of new complexes. In [Ru(dppbz)(CO)2Cl2] one of the two carbonyls undergoes facile displacement by neutral monodentate ligands (L) to afford complexes of the type [Ru(dppbz)(CO)(L)Cl2] (L = acetonitrile, 4-picoline and dimethyl sulfoxide). Both the carbonyls in [Ru(dppbz)(CO)2Cl2] are displaced on reaction with another equivalent of dppbz to afford [Ru(dppbz)2Cl2]. The two carbonyls and the two chlorides in [Ru(dppbz)(CO)2Cl2] could be displaced together by chelating mono-anionic bidentate ligands, viz. anions derived from 8-hydroxyquinoline (Hq) and 2-picolinic acid (Hpic) via loss of a proton, to afford the mixed-tris complexes [Ru(dppbz)(q)2] and [Ru(dppbz)(pic)2], respectively. The molecular structures of four selected complexes, viz. [Ru(dppbz)(CO)(dmso)Cl2], [Ru(dppbz)2Cl2], [Ru(dppbz)(q)2] and [Ru(dppbz)(pic)2], have been determined by X-ray crystallography. In dichloromethane solution, all the complexes show intense absorptions in the visible and ultraviolet regions. Cyclic voltammetry on the complexes shows redox responses within 0.71 to -1.24 V vs. SCE. [Ru(dppbz)(CO)2Cl2] has been found to serve as an excellent pre-catalyst for catalytic transfer-hydrogenation and Oppenauer oxidation.
- Mukherjee, Aparajita,Bhattacharya, Samaresh
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p. 15617 - 15631
(2021/05/19)
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- Synthesis and characterization of Merrifield resin and graphene oxide supported air stable oxidovanadium(IV) radical complexes for the catalytic oxidation of light aliphatic alcohols
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Imidazole modified Merrifield resin and (3-Aminopropyl)trimethoxysilane-modified graphene oxide supported oxidovanadium(IV) radical complexes PS-im-[VIVO(tbnC[rad])(acac)] (1) and GO-ATPMS-[VIVO(tbnO[rad])(acac)] (2) were synthesized and characterized by various spectroscopic, thermal and chemical techniques. The radical nature of 1 and 2 was established by trapping experiments in addition to EPR spectroscopy. In EPR analysis, complex 2 shows a prominent signal with g = 2.005, characteristic of an oxygen-centered radical. The neat complex [VIVO(tbnC[rad])(acac)] (A) displays an EPR signal at g = 2.0025, typical of carbon-centered radical. On the contrary, such characteristic EPR signal of a radical is absent in complex 1, presumably due to spin pairing. XPS analysis confirms the +4 oxidation state of vanadium in fresh as well as recycled catalysts 1 and 2. Both the supported complexes show excellent catalytic activity towards a variety of aliphatic alcohols. Comparatively, the polymer-supported complex displays better substrate conversion than the graphene oxide-supported complex. However, 2 shows better selectivity towards aldehydes, whereas carboxylic acids are obtained as major products in the presence of 1. Interestingly, catalyst 1 is almost equally effective towards all the examined alcohols, but its effectiveness reduces slightly for longer carbon chain alcohols. On the other hand, catalyst 2 shows better substrate conversion for the alcohols with a longer carbon chain. During the catalytic oxidation of alcohols, the active intermediate species oxidoperoxidovanadium(V) complex ([VO(O2)(tbn)(acac-H)]?) was detected by FT-IR, UV–vis, and LC–MS analysis.
- Chaudhary, Nikita,Haldar, Chanchal,Kesharwani, Neha
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- Effect of Nitro Derivatives of 1,2,4-Triazole on the Radiation-Induced Oxidation of Ethanol
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Abstract: The effect of 1,2,4-triazole and its nitro derivatives on the formation of final molecular products of radiation-induced transformations of oxygen-saturated ethanol has been studied. It has been found that the test compounds are almost not decomposed in the course of radiolysis, whereas they insignificantly decrease or do not affect the radiation-chemical yields of H2O2 and acetaldehyde. The experimental data indicate that the nitro derivatives of 1,2,4-triazole cannot compete with oxygen for α-hydroxyethyl radicals, and they do not interact with oxygen-centered radicals formed in the system. The reaction rate constant of the oxidation of α-hydroxyethyl radicals by the nitro derivatives of 1,2,4-triazole was found to be k ≤ 4.6 × 109 L mol?1 s?1 by calculation using the method of competing reactions.
- Brinkevich,Maliborskii, A. Ya.,Kapusto,Sverdlov,Grigor’ev, Yu. V.,Shadyro
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- Reactivity of vanadyl pyrophosphate catalyst in ethanol ammoxidation and β-picoline oxidation: Advantages and limitations of bi-functionality
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This study investigates the catalytic activity of vanadyl pyrophosphate (VPP) for both gas-phase ethanol ammoxidation to acetonitrile and β-picoline oxidation to nicotinic acid. Both reactions may be alternative processes to the industrial technologies used to produce these two chemicals. The reaction networks were investigated, also by feeding possible intermediates; in-situ DRIFT spectroscopy was used to monitor the interaction of ethanol and ammonia with the catalyst. VPP bi-functionality features played an important role in the two reactions; specifically, acidity was detrimental either because it catalyzed undesired reactions, such as ethanol dehydration to ethylene during ethanol ammoxidation, or because it caused a strong interaction with reactants – especially those containing N atoms, ammonia and β-picoline – thus giving rise to some surface saturation phenomena which inhibited the consecutive reactions leading to the final desired compounds, acetonitrile and nicotinic acid. The co-feeding of steam helped product desorption, thus enhancing selectivity in β-picoline oxidation.
- Tabanelli, Tommaso,Mari, Massimiliano,Folco, Federico,Tanganelli, Federico,Puzzo, Francesco,Setti, Laura,Cavani, Fabrizio
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- Selective Preparation of Olefins through Conversion of C2 and C3 Alcohols on NASICON-Type Phosphates
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Abstract—: We have studied the catalytic activity of LiZr2(PO4)3-based NASICON-type phosphates for conversion of C2 and C3 aliphatic alcohols with the aim of selectively preparing C2–C4 olefins. Selectivity has been controlled via partial heterovalent substitutions of In3+ or Nb5+ for Zr4+ or Mo for phosphorus. We have investigated the structure and morphology of the synthesized catalysts. The nature of the dopants has been shown to play a key role in determining the selectivity of the catalysts studied. Partial In3+ substitution for Zr4+ improves the dehydrogenating properties of the materials, whereas partial substitutions of Nb5+ for Zr4+ and Mo6+ for P5+ improve their dehydrating properties. We have demonstrated the possibility of highly selective preparation of ethylene and butylenes from ethanol and of propylene from propanol-1 and propanol-2.
- Ermilova, M. M.,Il’in, A. B.,Orekhova, N. V.,Yaroslavtsev, A. B.
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p. 693 - 700
(2021/07/26)
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- Kinetically Controlled Synthesis of Rhodium Nanocrystals with Different Shapes and a Comparison Study of Their Thermal and Catalytic Properties
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We report the synthesis of Rh nanocrystals with different shapes by controlling the kinetics involved in the growth of preformed Rh cubic seeds. Specifically, Rh nanocrystals with cubic, cuboctahedral, and octahedral shapes can all be obtained from the same cubic seeds under suitable reduction kinetics for the precursor. The success of such a synthesis also relies on the use of a halide-free precursor to avoid oxidative etching, as well as the involvement of a sufficiently high temperature to remove Br- ions from the seeds while ensuring adequate surface diffusion. The availability of Rh nanocrystals with cubic and octahedral shapes allows for an evaluation of the facet dependences of their thermal and catalytic properties. The data from in situ electron microscopy studies indicate that the cubic and octahedral Rh nanocrystals can keep their original shapes up to 700 and 500 °C, respectively. When tested as catalysts for hydrazine decomposition, the octahedral nanocrystals exhibit almost 4-fold enhancement in terms of H2 selectivity relative to the cubic counterpart. As for ethanol oxidation, the order is reversed, with the cubic nanocrystals being about three times more active than the octahedral sample.
- Zhao, Ming,Chen, Zitao,Shi, Yifeng,Hood, Zachary D.,Lyu, Zhiheng,Xie, Minghao,Chi, Miaofang,Xia, Younan
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p. 6293 - 6302
(2021/05/07)
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- Selective Butene Formation in Direct Ethanol-to-C3+-Olefin Valorization over Zn-Y/Beta and Single-Atom Alloy Composite Catalysts Using in Situ-Generated Hydrogen
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The selective production of C3+olefins from renewable feedstocks, especially via C1and C2platform chemicals, is a critical challenge for obtaining economically viable low-carbon middle-distillate transportation fuels (i.e., jet and diesel). Here, we report a multifunctional catalyst system composed of Zn-Y/Beta and “single-atom” alloy (SAA) Pt-Cu/Al2O3, which selectively catalyzes ethanol-to-olefin (C3+, ETO) valorization in the absence of cofed hydrogen, forming butenes as the primary olefin products. Beta zeolites containing predominately isolated Zn and Y metal sites catalyze ethanol upgrading steps (588 K, 3.1 kPa ethanol, ambient pressure) regardless of cofed hydrogen partial pressure (0-98.3 kPa H2), forming butadiene as the primary product (60% selectivity at an 87% conversion). The Zn-Y/Beta catalyst possesses site-isolated Zn and Y Lewis acid sites (at ~7 wt % Y) and Br?nsted acidic Y sites, the latter of which have been previously uncharacterized. A secondary bed of SAA Pt-Cu/Al2O3selectively hydrogenates butadiene to butene isomers at a consistent reaction temperature using hydrogen generatedin situfrom ethanol to butadiene (ETB) conversion. This unique hydrogenation reactivity at near-stoichiometric hydrogen and butadiene partial pressures is not observed over monometallic Pt or Cu catalysts, highlighting these operating conditions as a critical SAA catalyst application area for conjugated diene selective hydrogenation at high reaction temperatures (>573 K) and low H2/diene ratios (e.g., 1:1). Single-bed steady-state selective hydrogenation rates, associated apparent hydrogen and butadiene reaction orders, and density functional theory (DFT) calculations of the Horiuti-Polanyi reaction mechanisms indicate that the unique butadiene selective hydrogenation reactivity over SAA Pt-Cu/Al2O3reflects lower hydrogen scission barriers relative to monometallic Cu surfaces and limited butene binding energies relative to monometallic Pt surfaces. DFT calculations further indicate the preferential desorption of butene isomers over SAA Pt-Cu(111) and Cu(111) surfaces, while Pt(111) surfaces favor subsequent butene hydrogenation reactions to form butane over butene desorption events. Under operating conditions without hydrogen cofeeding, this combination of Zn-Y/Beta and SAA Pt-Cu catalysts can selectively form butenes (65% butenes, 78% C3+selectivity at 94% conversion) and avoid butane formation using onlyin situ-generated hydrogen, avoiding costly hydrogen cofeeding requirements that hinder many renewable energy processes.
- Allard, Lawrence F.,Assary, Rajeev S.,Cordon, Michael J.,Krause, Theodore R.,Kropf, A. Jeremy,Li, Zhenglong,Lin, Fan,Liu, Dongxia,Miller, Jeffrey T.,Purdy, Stephen C.,Unocic, Kinga A.,Wang, Huamin,Wegener, Evan C.,Yang, Ce,Zhang, Junyan,Zhou, Mingxia
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p. 7193 - 7209
(2021/06/30)
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- Study of Cu modified Zr and Al mixed oxides in ethanol conversion: The structure-catalytic activity relationship
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Here, we study the influence of the Cu modified (Zr + Ce)O2-Al2O3 systems composition and synthesis conditions on their catalytic properties in the ethanol conversion. First, we obtained varios ratios mixed Al-Zr supports at different synthesis temperatures using a sol-gel method. Then we modified the surface of the oxides by Cu, reduced in hydrogen flow. All obtained systems demonstrated а high alcohol conversion and selectivity to acetaldehyde. The surface area (SBET), the pore volume, and the pore distribution were measured by the nitrogen adsorption method. The structure of the samples have been investigated by XRD and XAS-spectroscopy. A correlation between the synthesis temperature and contents of mixed oxide support and textural properties were observed. The results show that Al-Zr mixed oxide support structure plays a crucial role in forming a Cu active site for ethanol dehydrogenation to acetaldehyde.
- Zhukova,Chuklina,Maslenkova
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p. 159 - 165
(2021/03/17)
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- Catalytic properties of the framework-structured zirconium-containing phosphates in ethanol conversion
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Aliphatic alcohols C1–C4 can serve as raw material for the production of essential organic products, such as olefins, aldehydes, ketones and ethers. For the development of catalysts of alcohols’ conversion, the authors considered two families of framework phosphate compounds with significant chemical, thermal and phase stability: NaZr2(PO4)3 (NZP/NASICON) and Sc2(WO4)3 (SW). Variation in the composition of zirconium-containing NZP- and SW-complex phosphates allows one to vary the number and strength of Lewis acid centers and incorporate oxidative-reducing centers (such as d-transition metals) into the structure. The phosphates M0.5+xNixZr2 ? x(PO4)3 (where M are Mn and Ca) were studied in the reactions of ethanol conversion. From the results of complex investigation, the compounds with M–Mn (x = 0, 0.3 and 0.5) were crystallized in the SW-type (monoclinic symmetry), while the phosphates with M–Ca (x = 0, 0.2 and 0.4) were characterized as the NZP-structured compounds (trigonal symmetry). The surface areas and pore volumes of synthesized catalysts varied, with different compositions, from 14 to 32?m2/g and 0.03 to 0.12?mL/g, respectively. From the catalytic experiments, the main direction of conversion on all the studied catalysts was ethanol dehydrogenization with acetaldehyde formation. The other conversion products—diethyl ether and ethylene—were produced with small yields. Based on the results obtained, the NZP-sample Ca0.5Zr2(PO4)3 can be considered as a selective catalyst for producing acetaldehyde at 400?°C with a yield of 55% from its theoretical amount.
- Mayorov, Pavel,Asabina, Elena,Zhukova, Anna,Osaulenko, Diana,Pet’kov, Vladimir,Lavrenov, Dmitry,Kovalskii, Andrey,Fionov, Alexander
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p. 3645 - 3659
(2021/06/02)
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- CATALYTIC CONVERSION OF ETHANOL TO 1-/2-BUTENES
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Simple and economical conversion of aqueous ethanol feed streams into butenes by a single step method using transition metal oxides on a silica supports under preselected processing conditions. By directly producing a C4-rich olefin mixture from an ethanol containing stream various advantages are presented including, but not limited to, significant cost reduction in capital expenses and operational expenses.
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Paragraph 0013-0022; 0026-0046
(2021/06/11)
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- Highly efficient visible-light photocatalytic ethane oxidation into ethyl hydroperoxide as a radical reservoir
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Photocatalytic ethane conversion into value-added chemicals is a great challenge especially under visible light irradiation. The production of ethyl hydroperoxide (CH3CH2OOH), which is a promising radical reservoir for regulating the oxidative stress in cells, is even more challenging due to its facile decomposition. Here, we demonstrated a design of a highly efficient visible-light-responsive photocatalyst, Au/WO3, for ethane oxidation into CH3CH2OOH, achieving an impressive yield of 1887 μmol gcat?1in two hours under visible light irradiation at room temperature for the first time. Furthermore, thermal energy was introduced into the photocatalytic system to increase the driving force for ethane oxidation, enhancing CH3CH2OOH production by six times to 11?233 μmol gcat?1at 100 °C and achieving a significant apparent quantum efficiency of 17.9% at 450 nm. In addition, trapping active species and isotope-labeling reactants revealed the reaction pathway. These findings pave the way for scalable ethane conversion into CH3CH2OOH as a potential anticancer drug.
- Zhu, Yao,Fang, Siyuan,Chen, Shaoqin,Tong, Youjie,Wang, Chunling,Hu, Yun Hang
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p. 5825 - 5833
(2021/05/07)
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- A chemiresistive methane sensor
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A chemiresistive sensor is described for the detection of methane (CH4), a potent greenhouse gas that also poses an explosion hazard in air. The chemiresistor allows for the low-power, low-cost, and distributed sensing of CH4 at room temperature in air with environmental implications for gas leak detection in homes, production facilities, and pipelines. Specifically, the chemiresistors are based on single-walled carbon nanotubes (SWCNTs) noncovalently functionalized with poly(4-vinylpyridine) (P4VP) that enables the incorporation of a platinum-polyoxometalate (Pt-POM) CH4 oxidation precatalyst into the sensor by P4VP coordination. The resulting SWCNT-P4VP-Pt-POM composite showed ppm-level sensitivity to CH4 and good stability to air as well as time, wherein the generation of a high-valent platinum intermediate during CH4 oxidation is proposed as the origin of the observed chemiresistive response. The chemiresistor was found to exhibit selectivity for CH4 over heavier hydrocarbons such as n-hexane, benzene, toluene, and o-xylene, as well as gases, including carbon dioxide and hydrogen. The utility of the sensor in detecting CH4 using a simple handheld multimeter was also demonstrated.
- Bezdek, Máté J.,Luo, Shao-Xiong Lennon,Ku, Kang Hee,Swager, Timothy M.
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- Core-shell nanoparticles with tensile strain enable highly efficient electrochemical ethanol oxidation
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The ethanol oxidation reaction (EOR), the anode reaction of direct ethanol fuel cells, suffers from sluggish oxidation kinetics and low selectivity toward complete oxidation to CO2. The key to solving the above problems is to design and synthesize high-performance catalysts. In this work, we synthesize Ag@AgPd core-shell nanoparticles that exhibit a significant improvement in catalytic performance. Specifically, in 1.0 M KOH + 1.0 M EtOH, the mass activity of the Ag@AgPd core-shell catalyst reaches up to 12.7 A mgPd?1with a significantly improved selectivity toward CO2by 4.5 times compared with commercial Pd/C. This superior performance guarantees that this Ag@AgPd core-shell nanoparticle is among the best-reported catalysts. Mechanism study by density functional theory shows that the tensile strain that originates from the unique core-shell structure decreases the potential determining step by 39%, which plays the most important role in increasing the activity and selectivity. This work demonstrates the effect of the tensile strain in promoting the kinetics and selectivity of the EOR, which may serve as a guide for the design of highly efficient electrocatalysts for general alcohol oxidation reactions by controlled nanoparticle synthesis.
- Cheng, Tao,Gao, Chuanbo,Jiang, Yilan,Liu, Kai,Liu, Moxuan,Liu, Zhaojun,Lu, Yiming,Wang, Xiaoxiao,Xie, Miao,Zhang, Qing,Zhang, Shumeng,Zhang, Zhixue
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supporting information
p. 15373 - 15380
(2021/07/21)
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- Mesoporous silica supported phosphotungstic acid catalyst for glycerol dehydration to acrolein
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Conversion of glycerol to acrolein is a useful reaction for value-added application of biodiesel-derived glycerol and bioenergy development. The high-performance solid acid catalyst is essential to this dehydration reaction. In this paper, tungsten-based heteropolyacids (HPA) were supported on non-ordered mesoporous silica (MSU-x) to increase their dispersion and used as catalysts for glycerol dehydration to acrolein. Aiming to reveal the surface structure of HPA and resulting acidic properties, as well as the relationship between acidic properties and dehydration activity, different loadings of H3PW12O40 were supported on MSU-x (10–50 wt%) and the catalysts were characterized by X-ray diffraction (XRD), BET, SEM/TEM, UV–vis diffuse reflectance spectra (DRS), Raman and FT-IR techniques. Their acidic properties were studied by NH3-Temperature Programmed Desorption (NH3-TPD) and Pyridine adsorption methods. The molecular structure and dispersion of H3PW12O40 supported on the catalysts was revealed. The Keggin unit preserved well but with different hydration level for various loadings. The total acid concentration and respective Br?nsted/Lewis acid identification were calculated. The acrolein yield increased with H3PW12O40 loading until 30 wt% and showed less change with higher loadings. Based on the correlation of acrolein formation rate with acidic properties, the active role of Br?nsted acid and the cooperative role of Br?nsted/Lewis acid sites for glycerol dehydration to acrolein were discussed. This work provides new insight into the structure evolution of heteropolyacids and the catalyst design for the glycerol to acrolein.
- Wang, Zhiheng,Liu, Licheng
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- Highly active carbon nanotube–promoted Rh-Mn-Li/SiO2 catalysts for the synthesis of C2+ oxygenates from syngas
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The effect of carbon nanotubes on the catalytic properties of Rh-Mn-Li/SiO2 catalysts was investigated for CO hydrogenation. The catalysts were comprehensively characterized by means of X-ray power diffraction, N2 sorption, transmission electron microscope, H2–temperature-programmed reduction, CO–temperature-programmed desorption, temperature-programmed surface reaction, and X-ray photoelectron spectroscopy. The results showed that an appropriate amount of carbon nanotubes can be attached to the surface of the SiO2 sphere and can improve the Rh dispersion. Moderate Rh-Mn interaction can be obtained by doping with the appropriate amount of carbon nanotubes, which promotes the formation of strongly adsorbed CO and facilitates the progress of CO insertion, resulting in the increase in the selectivity of C2+ oxygenate synthesis.
- Chen, Guoqing,Han, Ying,Mao, Dongsen,Mao, Haifang,Xiao, Xiuzhen,Yu, Jun
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p. 436 - 442
(2021/01/11)
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- Confined alkali metal ions in two-dimensional aluminum phosphate promoted activity for the condensation of lactic acid to 2,3-pentanedione
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The sustainable production of 2,3-pentanedione from bio-lactic acid was investigated over alkali metal ion-intercalated laminar aluminum phosphate. The confined alkali metal ion through the adjacent layers of aluminum phosphate offered excellent stability for the condensation of lactic acid to 2,3-pentanedione at least 80 h on stream, remaining constant at 55% conversion of lactic acid as well as around 80% of 2,3-pentanedione selectivity. The intercalated alkali metal ions can efficiently stabilize the enol intermediate, promoting the activity of lactic acid condensation. Besides, it can also prevent the occurrence of a layered stack of aluminum phosphate, providing an excellent mass transfer space for molecular diffusion, which is demonstrated by the calculation of the relation between molecular mean free paths for lactic acid and 2,3-pentanedione and the interlamellar spacing of aluminum phosphate. As a result, the alkali metal ion-intercalated laminar aluminum phosphate exhibited excellent performance for the condensation of lactic acid to 2,3-pentanedione at 270 °C, achieving 90% of lactic acid conversion and 80% of selectivity towards 2,3-pentanedione.
- Dai, Yunsheng,Li, Xinli,Tang, Congming,Yang, Chenglong,Zhang, Ju
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supporting information
p. 13806 - 13813
(2021/08/16)
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- Sustainable production of propionic acid: catalytic deoxygenation of lactic acid over MoOx/Fe
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The synergistic effect between Mo and Fe on deoxygenation of lactic acid to propionic acid was studied in this work. The catalyst structure and its chemical composites were characterized by XRD, FT-IR and EDS, respectively. The morphology of the catalyst was observed by SEM, and the reducibility was evaluated by H2-TPR. According to its structure characterization, Mo species were coated on the surface of iron powders as MoO3, and the interactions between Mo and Fe species were investigated by H2-TPR under calcination at high temperatures. A reduction peak at 650 °C moved toward low temperatures with the addition of an iron component, suggesting that iron promoted the reduction of Mo species. Due to this reason, catalytic performances are rapidly enhanced, being far more superior to any one of the Mo-Fe components. However, an excess of Fe content,ca.Fe/Mo molar ratios >0.908, decreases the activity on lactic acid deoxygenation, suggesting that the redox property of the catalyst is a major factor. Catalysts with Co and Ni substituting for Fe displayed lower selectivity to propionic acid, demonstrating that regulating appropriately the redox properties is a key to improve lactic acid deoxygenation again. The hydrothermal temperature and calcination temperature have an important influence on the formation of MoO3and its decomposition, which then affects its activity. Inspiringly, the catalyst with a Fe/Mo molar ratio of 0.908 offered an excellent stability, which proceeded efficiently for 120 h on stream under a high LHSV of 37 h?1at 390 °C.
- Chen, Zhi,Dai, Yunsheng,Li, Xinli,Pang, Jun,Tang, Congming,Wang, Hongqin,Yang, Chenglong
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p. 15831 - 15839
(2021/09/22)
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- Effect of sodium loading on Pt/ZrO2 during ethanol steam reforming
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Ethanol steam reforming (ESR) was investigated on unpromoted and several sodium promoted Pt/ZrO2 catalysts. From DRIFTS experiments, the following steps during ESR were inferred: dissociation of ethanol to produce ethoxy species; oxidative dehydrogenation of ethoxy species to acetate; and acetate decomposition. Acetate decomposition depends on the catalyst formulation. Decarboxylation is the most favored route at high sodium loading (2.5 and 5 wt.%); acetate decomposes in the forward direction to CH4 and a carbonate, which further decomposes to CO2. In contrast, decarbonylation is prevalent for the unpromoted catalyst or catalysts having low sodium loading. Acetate likely decomposes to CH3OH and CO. Adsorbed methanol may undergo further steam reforming by oxidative dehydrogenation to formate species, which decarbonylates via reverse decomposition to CO and H2O. Temperature programmed desorption/reaction and activity data confirmed that alkali promotion, especially at 1.8 %Na and higher loading, facilitates the forward acetate decomposition step, favoring decarboxylation over decarbonylation.
- Alhraki, Nour,Castro, Jonathan D.,Cronauer, Donald C.,Jacobs, Gary,Kropf, A. Jeremy,Martinelli, Michela,Matamoros, Maria E.
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- Low temperature steam reforming of ethanol over cobalt doped bismuth vanadate [Bi4(V0.90Co0.10)2O11-δ (BICOVOX)] catalysts for hydrogen production
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The atmospheric pressure low temperature steam reforming of ethanol over Bi4(V0.90Co0.10)2O11-δ (BICOVOX) catalysts, synthesize by a solution combustion synthesis method and calcined at 400, 600 and 800 °C, has been investigated at different reactor temperatures, H2O: EtOH molar ratios and feed flow rates. For fresh catalysts amount, crystallinity and particle size of pure γ-BICOVOX phase is observed to increase with increasing calcination temperature. Phase purity and crystallinity of the catalysts are almost retained till 30 h of activity study with some amount of carbon formation as derived from XRD, XPS, FESEM and simultaneous DTA-TGA study. Catalyst calcined at 600 °C (BICOVOX-600) exhibits the highest ethanol conversion (100%) with maximum H2 selectivity (80%) under reaction conditions of 400 °C, 23:1H2O: EtOH molar ratio and 0.35 cc min?1 feed flow rate. The maximum O2? vacancy present in lattice and lowest coke deposition could explain the best performance of BICOVOX-600 catalyst.
- Aich, Shampa,Roy, Banasri,Sharma, Shweta
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- Photoelectrochemical reduction of dissolved carbon dioxide over Ni(OH)2 into organic oxygenates
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Abstract: The hydrothermal method has been used to prepare Ni(OH)2 photocathode. The photoelectrochemical (PEC) reduction of CO2 over Ni(OH)2 has been conducted in 0.2?M LiClO4 in aqueous and N,N-dimethylformamide (DMF) medium under visible light irradiation. The thin film was characterized by XRD, UV–Vis, FTIR, FESEM-EDX, BET analysis, and electrochemical method for the determination of phases, bandgap energy, chemical bonding, surface morphology, elemental compositions, surface area, and electrochemical properties, respectively. Based on UV–Vis spectroscopy, the bandgap energy of Ni(OH)2 was 1.8?eV which enabled efficient visible light absorption for the photoreaction. The photocurrent density in aqueous and DMF solution at 0.2?V (vs. Ag/AgCl) was 24?mA?cm?2 and 5?mA?cm?2, respectively. Acetaldehyde and methanol are the products in aqueous solution, while formic acid and methanol are the products in DMF, after 6?h of photoelectrolysis. The product formations from the photoelectrochemical reduction of dissolved CO2 were 612 and 854?ppm in aqueous and DMF, respectively, where the Faradaic efficiency in aqueous and DMF is 24 and 33%, respectively. Furthermore, throughout the PEC study, the transformation of Ni(OH)2 to NiO plays a significant role in the formation of organic oxygenates from the reduction reaction of CO2. Graphic abstract: [Figure not available: see fulltext.]
- Che Mat, Ahmad Nazeer,Basirun, Wan Jefrey,Shahid, Muhammad Mehmood
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p. 1363 - 1372
(2021/01/07)
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- Substitution Reactions in the Pyrolysis of Acetone Revealed through a Modeling, Experiment, Theory Paradigm
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The development of high-fidelity mechanisms for chemically reactive systems is a challenging process that requires the compilation of rate descriptions for a large and somewhat ill-defined set of reactions. The present unified combination of modeling, experiment, and theory provides a paradigm for improving such mechanism development efforts. Here we combine broadband rotational spectroscopy with detailed chemical modeling based on rate constants obtained from automated ab initio transition state theory-based master equation calculations and high-level thermochemical parametrizations. Broadband rotational spectroscopy offers quantitative and isomer-specific detection by which branching ratios of polar reaction products may be obtained. Using this technique, we observe and characterize products arising from H atom substitution reactions in the flash pyrolysis of acetone (CH3C(O)CH3) at a nominal temperature of 1800 K. The major product observed is ketene (CH2CO). Minor products identified include acetaldehyde (CH3CHO), propyne (CH3CCH), propene (CH2CHCH3), and water (HDO). Literature mechanisms for the pyrolysis of acetone do not adequately describe the minor products. The inclusion of a variety of substitution reactions, with rate constants and thermochemistry obtained from automated ab initio kinetics predictions and Active Thermochemical Tables analyses, demonstrates an important role for such processes. The pathway to acetaldehyde is shown to be a direct result of substitution of acetone's methyl group by a free H atom, while propene formation arises from OH substitution in the enol form of acetone by a free H atom.
- Zaleski, Daniel P.,Sivaramakrishnan, Raghu,Weller, Hailey R.,Seifert, Nathan A.,Bross, David H.,Ruscic, Branko,Moore, Kevin B.,Elliott, Sarah N.,Copan, Andreas V.,Harding, Lawrence B.,Klippenstein, Stephen J.,Field, Robert W.,Prozument, Kirill
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p. 3124 - 3142
(2021/03/08)
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- Biocatalysed synthesis of chiral amines: continuous colorimetric assays for mining amine-transaminases
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In the course of our research aimed at the design of new biocatalytic processes for the enantioselective synthesis of chiral amines, we have developed new continuous assays for the screening of amine-transaminase collections. These assays are based on the use of hypotaurine as an irreversible amine donor. This β-aminosulfinic acid is converted upon transamination into 2-oxoethylsulfinic acid, which instantaneously decomposes into acetaldehyde and sulfite ions that can be easily detected by spectrophotometry using Ellman's reagent. Two complementary assays were developed based on this titration method. Firstly, a direct assay allowed detection of various transaminases able to use hypotaurine as an amino donor. In a second coupled assay,l-alanine is used as a generic donor substrate of amine-transaminases and is regenerated using an auxiliary hypotaurine-transaminase. The powerful and complementary nature of both assays was demonstrated through the screening of a collection of 549 amine-transaminases from biodiversity, thus allowing the discovery of a variety of valuable new biocatalysts for use in synthetic processes.
- Gourbeyre, Léa,Heuson, Egon,Charmantray, Franck,Hélaine, Virgil,Debard, Adrien,Petit, Jean-Louis,de Berardinis, Véronique,Gefflaut, Thierry
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p. 904 - 911
(2021/02/26)
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- Investigation of Cyclam Based Re-Complexes as Potential Electrocatalysts for the CO2 Reduction Reaction
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Among the various homogenous electrocatalysts, especially Re(bpy)(CO)3Cl and [Ni(cyclam)]2+ were shown to be highly efficient for the selective conversion of CO2 to CO at moderate potentials. However, a purposeful combination of a ReI tricarbonyl unit with a cyclam ligand hitherto received no attention. Herein, we report on a series of cyclam based Re complexes comprising the original {N4} as well as heteroatom-altered ligand frameworks, describe their synthesis, reveal their coordination behavior and furthermore investigate their performance towards the electrochemical CO2 reduction.
- Gerschel, Philipp,Cordes, Anna L.,Bimmermann, Sarah,Siegmund, Daniel,Metzler-Nolte, Nils,Apfel, Ulf-Peter
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p. 968 - 977
(2021/04/09)
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- Oxidative dehydrogenation of ethyl lactate to ethyl pyruvate over vanadium and iron antimonates catalysts
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The oxidative dehydrogenation of ethyl lactate to ethyl pyruvate, corresponding to the first step of a new process in the industrial production of methionine, has been investigated. Iron and vanadium antimonates were developed as catalysts, and were optimized to reach 87 % conversion of ethyl lactate, with 88 % selectivity to ethyl pyruvate, at only 275 °C. The catalysts were characterized before and after catalytic testing, and in situ using various techniques, including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and XANES spectroscopy. The results show that neither the Sb3+/Sb5+ nor the Fe2+/Fe3+ redox couple were involved in the dehydrogenation of ethyl lactate, or in the catalysts re-oxidation. The active and selective catalytic sites correspond to surface V5+ species. These species should not be considered as part of the bulk oxide, but as supra-surface species whose surface content is monitored with the bulk composition.
- Huchede,Morvan,Vera,Bellière-Baca,Millet
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- Copper-Containing Catalysts Based on Cerium–Zirconium Oxide Supports in Ethanol Conversion Reaction According to In Situ IR Spectroscopic Data
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Abstract: Copper-containing catalysts based on CeO2–ZrO2 solid solutions were prepared by the Pecini method and studied using a set of physicochemical methods. It was found that the bond strength of oxygen on the catalyst surface, which depends on the properties of supported copper oxide clusters and a ratio between CeO2 and ZrO2 in the support, plays a main role in ethanol conversion. Ethoxy groups, acetate and formate complexes, and condensation products were detected as main surface intermediates formed in the course of ethanol conversion on the catalysts. The decomposition of the formate complexes was the key stage in the formation of hydrogen. Its appearance on the surface of the catalysts was due to the competition between the reactions of formate and acetate complex formation for oxygen with suitable properties.
- Ilichev, A. N.,Korchak, V. N.,Matyshak, V. A.,Sil’chenkova, O. N.
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p. 404 - 417
(2021/06/14)
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- Facile Preparation of Methyl Phenols from Ethanol over Lamellar Ce(OH)SO4· xH2O
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Ethanol transformation with high product selectivity is a great challenge, especially for high weight molecules. Here, we show a combination study of kinetic, thermodynamic, and in situ spectroscopy measurements to probe the selective upgrading of ethanol over lamellar Ce(OH)SO4·xH2O catalysts, with 60-70% Ce3+ preserved during the catalysis. High methyl phenols (MPs) selectivity at ~80% within condensation products was achieved at ~50% condensation yield (3.0 kPa C2H5OH, 15 kPa H2, Ar balanced, 693 K, 1 atm, gas hourly space velocity (GHSV) ~5.4 min-1), with acetaldehyde, acetone, 4-heptanone, and 2-pentanone as the key reaction intermediates. Kinetic measurements with the assistance of isotope labeling proved that MPs generated from the kinetically relevant step (KRS) of C-C bond coupling of enolate nucleophilically attacks surface C2H4O following a Langmuir-Hinshelwood model. Low ethanol and water pressures and high acetaldehyde and hydrogen pressures were proved to be favored for MPs generation rather than dehydration, in which hydrogen could reduce the amount of lattice oxygen and facilitate the preparation of MPs while water and ethanol both compete with acetaldehyde for active sites during catalysis. On the basis of in situ X-ray diffraction (XRD), quasi-in situ X-ray photoelectron spectroscopy (XPS), and Raman characterizations, the Ce(OH)SO4 crystal structure was proved to be maintained along with ethanol activation, and the Ce3+-OH Lewis acid-base pair was proved to be the active species for the selective C-C bond coupling. The KRS assumption was also supported by the apparent activation energy assessment within the reaction network on dehydration, dehydrogenation, aldol condensation, and cyclization and a series of negligible kinetic isotope effects (KIEs). This system can be easily extended to some other systems related to C-C bond coupling and is attracting attention on converting oxygenate platform molecules over lanthanide species.
- Guo, Jinqiu,Feng, Zongjing,Xu, Jun,Zhu, Jie,Zhang, Guanghui,Du, Yaping,Zhang, Hongbo,Yan, Chunhua
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p. 6162 - 6174
(2021/05/29)
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- Engineering the large pocket of an (S)-selective transaminase for asymmetric synthesis of (S)-1-amino-1-phenylpropane
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Amine transaminases offer an environmentally benign chiral amine asymmetric synthesis route. However, their catalytic efficiency towards bulky chiral amine asymmetric synthesis is limited by the natural geometric structure of the small pocket, representing a great challenge for industrial applications. Here, we rationally engineered the large binding pocket of an (S)-selective ?-transaminase BPTA fromParaburkholderia phymatumto relieve the inherent restriction caused by the small pocket and efficiently transform the prochiral aryl alkyl ketone 1-propiophenone with a small substituent larger than the methyl group. Based on combined molecular docking and dynamic simulation analyses, we identified a non-classical substrate conformation, located in the active site with steric hindrance and undesired interactions, to be responsible for the low catalytic efficiency. By relieving the steric barrier with W82A, we improved the specific activity by 14-times compared to WT. A p-p stacking interaction was then introduced by M78F and I284F to strengthen the binding affinity with a large binding pocket to balance the undesired interactions generated by F44. T440Q further enhanced the substrate affinity by providing a more hydrophobic and flexible environment close to the active site entry. Finally, we constructed a quadruple variant M78F/W82A/I284F/T440Q to generate the most productive substrate conformation. The 1-propiophenone catalytic efficiency of the mutant was enhanced by more than 470-times in terms ofkcat/KM, and the conversion increased from 1.3 to 94.4% compared with that of WT, without any stereoselectivity loss (ee > 99.9%). Meanwhile, the obtained mutant also showed significant activity improvements towards various aryl alkyl ketones with a small substituent larger than the methyl group ranging between 104- and 230-fold, demonstrating great potential for the efficient synthesis of enantiopure aryl alkyl amines with steric hindrance in the small binding pocket.
- Liu, He,Wang, Hualei,Wei, Dongzhi,Xie, Youyu,Xu, Feng,Xu, Xiangyang,Yang, Lin
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p. 2461 - 2470
(2021/04/22)
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- A study on the cataluminescence of propylene oxide on FeNi layered double hydroxides/graphene oxide
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In this work, FeNi layered double hydroxides/graphene oxide (FeNi LDH/GO) was prepared, which exhibits excellent selective cataluminescent performance towards propylene oxide. The selectivity and sensitivity of the cataluminescence (CTL) reaction were investigated in detail. Moreover, the catalytic reaction mechanism, including the intermediate products and the conversion of reactants to products, was discussed based on both the experimental and computational results. Furthermore, the proposed FeNi LDH/GO based CTL sensor was successfully applied for the determination of propylene oxide residue in fumigated raisins, which indicates extensive application potential for rapid food safety evaluation.
- Li, Ming,Hu, Yufei,Li, Gongke
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p. 11823 - 11830
(2021/07/11)
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- Kinetic and Structural Analysis of Two Linkers in the Tautomerase Superfamily: Analysis and Implications
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The tautomerase superfamily (TSF) is a collection of enzymes and proteins that share a simple β-α-β structural scaffold. Most members are constructed from a single-core β-α-β motif or two consecutively fused β-α-β motifs in which the N-terminal proline (Pro-1) plays a key and unusual role as a catalytic residue. The cumulative evidence suggests that a gene fusion event took place in the evolution of the TSF followed by duplication (of the newly fused gene) to result in the diversification of activity that is seen today. Analysis of the sequence similarity network (SSN) for the TSF identified several linking proteins ("linkers") whose similarity links subgroups of these contemporary proteins that might hold clues about structure-function relationship changes accompanying the emergence of new activities. A previously uncharacterized pair of linkers (designated N1 and N2) was identified in the SSN that connected the 4-oxalocrotonate tautomerase (4-OT) and cis-3-chloroacrylic acid dehalogenase (cis-CaaD) subgroups. N1, in the cis-CaaD subgroup, has the full complement of active site residues for cis-CaaD activity, whereas N2, in the 4-OT subgroup, lacks a key arginine (Arg-39) for canonical 4-OT activity. Kinetic characterization and nuclear magnetic resonance analysis show that N1 has activities observed for other characterized members of the cis-CaaD subgroup with varying degrees of efficiencies. N2 is a modest 4-OT but shows enhanced hydratase activity using allene and acetylene compounds, which might be due to the presence of Arg-8 along with Arg-11. Crystallographic analysis provides a structural context for these observations.
- Baas, Bert-Jan,Babbitt, Patricia C.,De Ruijter, Marieke,Erwin, Kaci,Johnson, William H.,Kaoud, Tamer S.,Lancaster, Emily B.,Levieux, Jake A.,Medellin, Brenda P.,Moreno, R. Yvette,Whitman, Christian P.,Zhang, Yan Jessie
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p. 1776 - 1786
(2021/06/21)
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- Converging conversion - using promiscuous biocatalysts for the cell-free synthesis of chemicals from heterogeneous biomass
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Production of chemicals from lignocellulosic biomass has been proposed as a suitable replacement to petrochemicals. However, one inherent challenge of biomass utilization is the heterogeneity of the substrate resulting in the presence of mixed sugars after hydrolysis. Fermentation of mixed sugars often leads to poor yield and generation of multiple by-products, thus complicating the subsequent downstream processing. System biocatalysis has thus been developed in recent years to address this challenge. In this work, several novel enzymes with broad substrate promiscuity were identified using a sequence-based discovery approach as suitable biocatalysts in a conversion ofd-xylose andl-arabinose, two major constituents of hemicellulose found in plant biomass. These promiscuous enzymes enabled simultaneous biotransformation ofd-xylose andl-arabinose to yield 1,4-butanediol (BDO) with a maximum production rate of 3 g L?1h?1and a yield of >95%. This model system was further adapted toward the production of α-ketoglutarate (2-KG) from the pentoses using O2as a cosubstrate for cofactor recycling reaching a maximum production rate of 4.2 g L?1h?1and a yield of 99%. To verify the potential applicability of our system, we attempted to scale up the BDO and 2-KG production fromd-xylose andl-arabinose. Simple optimization and reaction engineering allowed us to obtain BDO and 2-KG titers of 18 g L?1and 42 g L?1, with theoretical yields of >75% and >99%, respectively. One of the promiscuous enzymes identified together with auxiliary promiscuous enzymes was also suitable for stereoconvergent synthesis from a mixture ofd-glucose andd-galactose, predominant sugars found in food waste streams and microalgae biomass.
- Pick, André,Sieber, Volker,Sutiono, Samuel
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supporting information
p. 3656 - 3663
(2021/06/06)
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- A New Hexagonal Cobalt Nanosheet Catalyst for Selective CO2Conversion to Ethanal
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We report a new form of catalyst based on ferromagnetic hexagonal-close-packed (hcp) Co nanosheets (NSs) for selective CO2RR to ethanal, CH3CHO. In all reduction potentials tested from ?0.2 to ?1.0 V (vs RHE) in 0.5 M KHCO3solution, the reduction yields ethanal as a major product and ethanol/methanol as minor products. At ?0.4 V, the Faradaic efficiency (FE) for ethanal reaches 60% with current densities of 5.1 mA cm-2and mass activity of 3.4 A g-1(total FE for ethanal/ethanol/methanol is 82%). Density functional theory (DFT) calculations suggest that this high CO2RR selectivity to ethanal on the hcp Co surface is attributed to the unique intralayer electron transfer, which not only promotes [OC-CO]* coupling but also suppresses the complete hydrogenation of the coupling intermediates to ethylene, leading to highly selective formation of CH3CHO.
- Huang, Bolong,Jin, Jing,Lin, Honghong,Ma, Zhenhui,Muzzio, Michelle,Peng, Yong,Shen, Mengqi,Sun, Mingzi,Sun, Shouheng,Xi, Pinxian,Yan, Chun-Hua,Yin, Jie,Yin, Zhouyang,Yu, Chao,Zhang, Hong
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supporting information
p. 15335 - 15343
(2021/10/01)
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- Photolytic Activation of Late-Transition-Metal-Carbon Bonds and Their Reactivity toward Oxygen
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The photolytic activation of palladium(II) and platinum(II) complexes [M(BPI)(R)] (R = alkyl, aryl) featuring the 1,3-bis(2-pyridylimino)isoindole (BPI) ligand has been investigated in various solvents. In the absence of oxygen, the formation of chloro complexes [M(BPI)Cl] is observed in chlorinated solvents, most likely due to the photolytic degradation of the solvent and formation of HCl. The reactivity of the complexes toward oxygen has been studied both experimentally and computationally. Excitation by UV irradiation (365 nm) of the metal complexes [Pt(BPI)Me] and [Pd(BPI)Me] leads to distortion of the square-planar coordination geometry in the excited triplet state and a change in the electronic structure of the complexes that allows the interaction with oxygen. TD-DFT computational studies suggest that, in the case of palladium, the Pd(III) superoxide intermediate [Pd(BPI)(κ1-O2)Me] is formed and, in the case of platinum, the Pt(IV) peroxide intermediate [Pt(BPI)(κ2-O2)Me]. For alkyl complexes where metal-carbon bonds are sufficiently weak, the photoactivation leads to the insertion of oxygen into the metal-carbon bond to generate alkylperoxo complexes: for example [Pd(BPI)OOMe], which has been isolated and structurally characterized. For stronger M-C(aryl) bonds, the reaction of [Pt(BPI)Ph] with O2 and light results in a Pt(IV) complex, tentatively assigned as the peroxo complex [Pt(BPI)(κ2-O2)Ph], which in chlorinated solvents reacts further to give [Pt(BPI)Cl2Ph], which has been isolated and characterized by scXRD. In addition to the facilitation of oxygen insertion reactions, UV irradiation can also affect the reactivity of other components in the reaction mixture, such as the solvent or other reaction products, which can result in further reactions. Labeling studies using [Pt(BPI)(CD3)] in chloroform have shown that photolytic reactions with oxygen involve degradation of the solvent.
- Britovsek, George J. P.,De Aguirre, Adiran,Ho, Sarah K. Y.,Lam, Francis Y. T.,Maseras, Feliu,White, Andrew J. P.
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supporting information
p. 4077 - 4091
(2021/12/17)
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- AEROBIC ELECTROCATALYTIC OXIDATION OF HYDROCARBONS
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This invention is directed to a method of oxygenating hydrocarbons with molecular oxygen, O2, as oxidant under electrochemical reducing conditions, using polyoxometalate compounds containing copper such as Q10 [Gu4(H2O)2(B-α-PW9O)2] or Q12{ [Cu(H2O)]3[(A-α- PW9O34)2(NO3)-] } or solvates thereof as catalysts, wherein Q are each independently selected from alkali metal cations, alkaline earth metal cations, transition metal cations, NH4+,H+ or any combination thereof.
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Paragraph 0074
(2022/01/04)
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- Surfactant-Assisted Ozonolysis of Alkenes in Water: Mitigation of Frothing Using Coolade as a Low-Foaming Surfactant
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Aqueous-phase ozonolysis in the atmosphere is an important process during cloud and fog formation. Water in the atmosphere acts as both a reaction medium and a reductant during the ozonolysis. Inspired by the atmospheric aqueous-phase ozonolysis, we herein report the ozonolysis of alkenes in water assisted by surfactants. Several types of surfactants, including anionic, cationic, and nonionic surfactants, were investigated. Although most surfactants enhanced the solubility of alkenes in water, they also generated excessive foaming during the ozone bubbling, which led to the loss of products. Mitigation of the frothing was accomplished by using Coolade as a nonionic and low-foaming surfactant. Coolade-assisted ozonolysis of alkenes in water provided the desired carbonyl products in good yields and comparable to those achieved in organic solvents. During the ozonolysis reaction, water molecules trapped within the polyethylene glycol region of Coolade were proposed to intercept the Criegee intermediate to provide a hydroxy hydroperoxide intermediate. Decomposition of the hydroxy hydroperoxide led to formation of the carbonyl product without the need for a reductant typically required for the conventional ozonolysis using organic solvents. This study presents Coolade as an effective surfactant to improve the solubility of alkenes while mitigating frothing during the ozonolysis in water.
- Buntasana, Supanat,Hayashi, Jun,Klumphu, Piyatida,Padungros, Panuwat,Saetung, Prakorn,Vilaivan, Tirayut
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supporting information
(2022/02/23)
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- Interfacial Sites in Ag Supported Layered Double Oxide for Dehydrogenation Coupling of Ethanol to n-Butanol
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Upgrading of ethanol to n-butanol through dehydrogenation coupling has received increasing attention due to the wide application of n-butanol. But the enhancement of ethanol dehydrogenation and followed coupling to produce high selectivity to n-butanol is still highly desired. Our previous work has reported an acid-base-Ag synergistic catalysis, with Ag particles supported on Mg and Al-containing layered double oxides (Ag/MgAl-LDO). Here, Ag-LDO interfaces have been manipulated for dehydrogenation coupling of ethanol to n-butanol by tailoring the size of Ag particles and the interactions between Ag and LDO. It has been revealed that increasing the population of surface Ag sites at Ag-LDO interfaces promotes not only the dehydrogenation of ethanol to acetaldehyde but also the subsequent aldol condensation of generated acetaldehyde. A selectivity of up to 76 % to n-butanol with an ethanol conversion of 44 % has been achieved on Ag/LDO with abundant interfacial Ag sites, much superior to the state-of-the-art catalysts.
- Zhang, Jian,Shi, Kai,Zhu, Yanru,An, Zhe,Wang, Wanning,Ma, Xiaodan,Shu, Xin,Song, Hongyan,Xiang, Xu,He, Jing
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p. 1095 - 1103
(2021/02/01)
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- First row transition metals on the ethanol Guerbet reaction: Products distribution and structural behavior of mixed metal oxides as catalysts
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Described is the transformation of ethanol into 1-butanol, acetaldehyde and other products by the Guerbet reaction (GR) over mixed metal oxides (MMOs) as catalysts. The MMOs, in which Mg2+ was partially (20 mol%) substituted by Fe2+, Co2+, Ni2+, Cu2+, and Zn2+, were obtained from hydrotalcite precursors and the reactions conducted in a fixed bed flow reactor. EPR was used to observe oxygen vacancies after the catalytic reactions, which may be related to the ethanol reactivity due to the basicity enhancement of the catalyst. Carbon deposition, mostly filamentous, was observed in all catalysts and a trend between the metal-carbon bond energy and the percentage of deposited carbon was established. This correlation and the catalyst product distribution can be useful to tailor new catalysts. Using four parameters, ethanol conversion, 1-butanol and side-product selectivities and percentage of carbon deposition, Zn20MMO proved to be the best choice for GR.
- Boscolo, Mauricio,Metzker, Gustavo,Mora Vargas, Jorge Andres,Perrone, Olavo Micali,Siqueira, Marcos Rechi,Varanda, Laudemir Carlos,de Lima, Livia Padilha
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- Catalytic Hydrogenation of Trivinyl Orthoacetate: Mechanisms Elucidated by Parahydrogen Induced Polarization
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Parahydrogen (pH2) induced polarization (PHIP) is a unique method that is used in analytical chemistry to elucidate catalytic hydrogenation pathways and to increase the signal of small metabolites in MRI and NMR. PHIP is based on adding or exchanging at least one pH2 molecule with a target molecule. Thus, the spin order available for hyperpolarization is often limited to that of one pH2 molecule. To break this limit, we investigated the addition of multiple pH2 molecules to one precursor. We studied the feasibility of the simultaneous hydrogenation of three arms of trivinyl orthoacetate (TVOA) intending to obtain hyperpolarized acetate. It was found that semihydrogenated TVOA underwent a fast decomposition accompanied by several minor reactions including an exchange of geminal methylene protons of a vinyl ester with pH2. The study shows that multiple vinyl ester groups are not suitable for a fast and clean (without any side products) hydrogenation and hyperpolarization that is desired in biochemical applications.
- Pravdivtsev, Andrey N.,Brahms, Arne,Kienitz, Stephan,S?nnichsen, Frank D.,H?vener, Jan-Bernd,Herges, Rainer
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p. 370 - 377
(2021/02/09)
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- Operando Investigation of Ag-Decorated Cu2O Nanocube Catalysts with Enhanced CO2 Electroreduction toward Liquid Products
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Direct conversion of carbon dioxide into multicarbon liquid fuels by the CO2 electrochemical reduction reaction (CO2RR) can contribute to the decarbonization of the global economy. Here, well-defined Cu2O nanocubes (NCs, 35 nm) uniformly covered with Ag nanoparticles (5 nm) were synthesized. When compared to bare Cu2O NCs, the catalyst with 5 at % Ag on Cu2O NCs displayed a two-fold increase in the Faradaic efficiency for C2+ liquid products (30 % at ?1.0 VRHE), including ethanol, 1-propanol, and acetaldehyde, while formate and hydrogen were suppressed. Operando X-ray absorption spectroscopy revealed the partial reduction of Cu2O during CO2RR, accompanied by a reaction-driven redispersion of Ag on the CuOx NCs. Data from operando surface-enhanced Raman spectroscopy further uncovered significant variations in the CO binding to Cu, which were assigned to Ag?Cu sites formed during CO2RR that appear crucial for the C?C coupling and the enhanced yield of liquid products.
- Herzog, Antonia,Bergmann, Arno,Jeon, Hyo Sang,Timoshenko, Janis,Kühl, Stefanie,Rettenmaier, Clara,Lopez Luna, Mauricio,Haase, Felix T.,Roldan Cuenya, Beatriz
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supporting information
p. 7426 - 7435
(2021/02/26)
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- Site-Specific Oxidation of (sp3)C-C(sp3)/H Bonds by NaNO2/HCl
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A site-specific oxidation of (sp3)C-C(sp3) and (sp3)C-H bonds in aryl alkanes by the use of NaNO2/HCl was explored. The method is chemical-oxidant-free, transition-metal-free, uses water as the solvent, and proceeds under mild conditions, making it valuable and attractive to synthetic organic chemistry.
- Zhao, Jianyou,Shen, Tong,Sun, Zhihui,Wang, Nengyong,Yang, Le,Wu, Jintao,You, Huichao,Liu, Zhong-Quan
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supporting information
p. 4057 - 4061
(2021/05/26)
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- A study of ethanol dehydrogenation to acetaldehyde over copper/zinc aluminate catalysts
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Catalysts composed of copper supported on ZnAl2O4 were prepared by conventional impregnation of a commercial zinc aluminate powder using copper nitrate water solutions. The fresh catalysts were characterized by XRD, skeletal IR and DR-UV–vis spectroscopies, FE-SEM microscopy, BET and pore volume measurements. The catalysts were tested in the conversion of ethanol (96percent assay, 6.9percent vol in nitrogen) at GHSV 10,000 h?1. The spent catalysts were characterized by FESEM and DR-UV–vis. These catalysts are very efficient for the dehydrogenation of ethanol to acetaldehyde, with selectivities in excess of 95percent at low conversion, persisting also at total conversion, allowing yields up to 90percent. The most active species appear to be on copper metal nanoparticles grown over Zn-poor substoichiometric spinel nanoparticles. The catalysts reduce themselves on stream. The high selectivity at low temperature is in part due to the ability of copper to kill the dehydration activity of the zinc aluminate support to diethyl ether. The selectivity to acetaldehyde decreases at very high temperature (> 673 K) due to overconversion of acetaldehyde to thermodynamically more stable products such as methane, acetone, propene and carbon oxides, as well as to increased competition with the more favored dehydration reaction. IR studies show the intermediate role of surface ethoxy-groups.
- Garbarino, Gabriella,Riani, Paola,Villa García, María,Finocchio, Elisabetta,Sanchez Escribano, Vicente,Busca, Guido
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p. 167 - 175
(2019/02/05)
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- Calcium Carbide Looping System for Acetaldehyde Manufacturing from Virtually any Carbon Source
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A vinylation/devinylation looping system for acetaldehyde manufacturing was evaluated. Vinylation of iso-butanol with calcium carbide under solvent-free conditions was combined with hydrolysis of the resulting iso-butyl vinyl ether under slightly acidic conditions. Acetaldehyde produced by hydrolysis was collected from the reaction mixture by simple distillation, and the remaining alcohol was redirected to the vinylation step. All the inorganic co-reagents can be looped as well, and the full sequence is totally sustainable. A complete acetaldehyde manufacturing cycle was proposed on the basis of the developed procedure. The cycle was fed with calcium carbide and produced the aldehyde as a single product in a total preparative yield of 97 %. No solvents, hydrocarbons, or metal catalysts were needed to maintain the cycle. As calcium carbide in principle can be synthesized from virtually any source of carbon, the developed technology represents an excellent example of biomass and waste conversion into a valuable industrial product.
- Rodygin, Konstantin S.,Lotsman, Kristina A.,Ananikov, Valentine P.
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p. 3679 - 3685
(2020/06/17)
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- Gas-Phase Dehydration of Glycerol into Acrolein in the Presence of Polyoxometalates
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Abstract: The activity of catalytic systems based on polyoxometalates in the gas-phase dehydration of glycerol into acrolein has been investigated. The catalysts synthesized have been characterized using FTIR spectroscopy, X-ray phase analysis, scanning electron microscopy, and low-temperature nitrogen adsorption/desorption (BET method). It has been shown that the nature of the surface acid sites of catalysts has a significant effect on the direction of glycerol transformation. An increase in the fraction of Br?nsted acid sites in the catalyst leads to an increase in the yield of acrolein. At the same time, an increase in the fraction of Lewis acid sites in the catalyst leads to an increase to the yield of acetol, which is formed through a competing route. Among the catalytic systems considered, the best results have been obtained with the silicomolybdic acid anion supported onto alumina (SiMo/A). The main patterns of the gas-phase glycerol dehydration have been studied using SiMo/A as a catalyst, and the conditions responsible for the highest yield of acrolein have been determined.
- Belousov, A. S.,Esipovich, A. L.,Kanakov, E. A.,Otopkova, K. V.,Shishulina, A. V.,Uvarova, V. D.,Vorotyntsev, A. V.
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p. 595 - 602
(2020/08/05)
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- Highly active and durable WO3/Al2O3catalysts for gas-phase dehydration of polyols
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Gas-phase glycerol dehydration over WO3/Al2O3catalysts was investigated. WO3loading on γ-Al2O3significantly affected the yield of acrolein and the catalyst with 20 wt% WO3loading showed the highest activity. The WO3/Al2O3catalyst with 20 wt% WO3loading showed higher activity and durability than the other supported WO3catalysts and zeolites. The number of Br?nsted acid sites and mesopores of the WO3/Al2O3catalyst did not decrease after the reaction, suggesting that glycerol has continuous access to Br?nsted acid sites inside the mesopores of WO3/Al2O3, thereby sustaining a high rate of formation of acrolein. Dehydration under O2flow further increased the durability of the WO3/Al2O3catalyst, enabling the sustainable formation of acrolein. In addition, the WO3/Al2O3catalyst with 20 wt% WO3loading showed high activity for the dehydration of various polyols to afford the corresponding products in high yield.
- Aihara, Takeshi,Asazuma, Katsuya,Miura, Hiroki,Shishido, Tetsuya
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p. 37538 - 37544
(2020/10/19)
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- Synthetic method of dapoxetine and intermediate thereof
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The invention discloses a synthetic method of dapoxetine and its intermediate, i.e., (S)-3-(tert-butyloxycarbonyl)amino-3-phenylpropanol as shown in a formula 5 which is described in the specification. The synthetic method of (S)-3-(tert-butyloxycarbonyl)amino-3-phenylpropanol is as shown in a synthesis route which is described in the specification, wherein a compound 3 and acetaldehyde are subjected to a Mannich reaction in an organic solvent under the action of a supramolecular catalyst constructed by a chiral catalyst and a polymer so as to obtain a compound 4, and the polymer is at least one selected from of the group consisting of PEG 200, PEG 400, PEG 600, MeOPEG 750, PEG 800, PEG 1000, PPG 800 and PPG 1000. The dapoxetine is synthesized from the (S)-3-(tert-butyloxycarbonyl)amino-3-phenylpropanol prepared by using the above method according to steps as shown in the synthesis route. The synthetic method of dapoxetine and the intermediate thereof has the characteristics of usage of cheap and easily available raw materials, high yield and low cost, and is more beneficial to industrial production.
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Paragraph 0093-0094
(2020/03/09)
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- Novel Si(II)+and Ge(II)+Compounds as Efficient Catalysts in Organosilicon Chemistry: Siloxane Coupling Reaction ?
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Novel catalytically active cationic Si(II) and Ge(II) compounds were synthesized and isolated in pure form. The Ge(II)+-based compounds proved to be stable against air and moisture and therefore can be handled very easily. All compounds efficiently catalyze the oxidative coupling of hydrosil(ox)anes with aldehydes and ketones as oxidation reagents and simultaneously the reductive ether coupling at very low amounts of 0.01 mol %. Because the catalysts also catalyze the reversible cyclotrimerization of aldehydes, paraldehyde can be used as a convenient source for acetaldehyde in siloxane coupling. It is shown that the reaction is especially suitable to make siloxane copolymers. Moreover, a new fluorine-free weakly coordinating boronate anion, B(SiCl3)4-, was successfully combined with the Si(II) and Ge(II) cations to give the stable catalytically active ion pairs Cp*Si:+B(SiCl3)4-, Cp*Ge:+B(SiCl3)4-, and [Cp(SiMe3)3Ge:+]B(SiCl3)4-.
- Fritz-Langhals, Elke,Kneissl, Sotirios,Piroutek, Phillip,Werge, Sven
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- Role of oxygen vacancies and Mn4+/Mn3+ ratio in oxidation and dry reforming over cobalt-manganese spinel oxides
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Spinel type cobalt-manganese oxides MnxCo3-xO4 (x = 0; 0.05; 0.10; 0.15) were prepared by co-precipitation method, from cobalt and manganese salts in the presence of ammonium carbonate. X-ray diffraction (XRD), texture measurements (BET/BJH), Fourier transform infrared spectroscopy (FT-IR), Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) were used for their characterization. Their catalytic behavior in ethanol combustion, dry reforming with CO2 and dehydrogenation was investigated. The results showed that the cubic structure of Co3O4, corresponding to spinel network, is not disturbed by adding manganese. Results obtained revealed that Mn0.15Co2.85O4 catalyst, with the highest content of Mn4+ cations in the octahedral sites and oxygen defects, display superior catalytic activity compared to the others. The apparent activation energies, calculated from Arrhenius plots, are as follows: Ea combustion a non-oxidative dehydrogenation a dry reforming, showing that cobalt-manganese spinel type oxides are good candidates for combustion.
- Mitran, Gheorghi?a,Chen, Shaojiang,Seo, Dong-Kyun
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