- Oxidation of methane and ethylene in water at ambient conditions
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Available spectroscopic, labelling and reactivity data show that stable μ-nitrido diiron phthalocyanine activates H2O2 to form a high-valent diiron oxo species. This species is a very powerful oxidant which oxidizes methane in pure water at 25-60 °C to methanol, formaldehyde and formic acid. The catalytic activity can significantly be increased in the presence of a diluted acid solution. Thus, a high turnover number of 209 was attained in 0.075 M H2SO4. Oxidation of ethylene resulted in the formation of formic acid as a major product and formaldehyde with high turnover numbers. Under optimal conditions, 426 mol HCOOH and 37 mol CH 2O per mole of catalyst were obtained in pure water. The practical and green features of this novel approach (H2O2 as the clean oxidant, water as the clean reaction medium, easily accessible solid catalyst) as well as the relevance to biological oxidation (binuclear structure of bio-inspired complex) are of great importance both from practical and fundamental points of view.
- Sorokin,Kudrik,Alvarez,Afanasiev,Millet,Bouchu
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- Partial Oxidation of Methane by Nitrous Oxide over Molybdenum Oxide supported on Silica
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Methanol and formaldehyde were formed as major products at a moderate conversion level (16percent) in the partial oxidation of methane by nitrous oxide in the presence of water over molybdenum oxide supported on silica.
- Liu, R.-S.,Iwamoto, M.,Lunsford, Jack H.
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- Flash Photolysis Study of the CH3O2 + CH3O2 Reaction: Rate Constants and Branching Ratios from 248 to 573 K
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The reactions 2CH3O2 -> 2CH3O + O2 (1a), 2CH3O2 -> CH3OH + HCHO + O2 (1b), and 2CH3O2 -> CH3COOH + O2 (1c) have been studied at temperatures between 248 and 573 K.At temperature above 373 K, the resulting decay traces were distorted away from pure second order at short wavelenghts (around 210 nm), owing to the presence of the hydroperoxy radicals formed via the nonterminating pathway (1a) and the subsequent rapid step CH3O + O2 -> HCHO + HO2 (2).This distortion enabled the nonterminating/terminating branching ratio, β, to be determined.Combining the present resultswith previously published work on the branching ratios gave lnβ=3.80-1470/T.Thus, although reaction 1 acts as a termination reaction under atmospheric conditions, it largely serves to convert CH3O2 into HO2 under combustion conditions.The temperature dependence of β enabled the real constant for the reaction k1, to be obtained over the entire experimental temperature range, giving k1 = 1.3E-13exp(365/T)cm31/molecule1/s, with ?2A/cm6molecule-2s-2 = 2.00E-28, ?2E/R/K2 = 1712, and ?2AE/R/cm3molecule-1s-1 = -5.61E-13.Absolute uncertainties, including contributions from both the experimental measurements and the dependence of k1 on various analysis parameters, are estimated to be 22percent, independent of temperature.No dependence of either the branching ratio or k1 on the total pressure was found.The mechanism of the title reaction is discussed and the present results are compared with existing studies of alkylperoxy self-reactions.The implications for combustion and atmospheric modeling are also discussed.
- Lightfoot, P. D.,Lesclaux, R.,Veyret, B.
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- Epidoxoform: A hydrolytically more stable anthracycline-formaldehyde conjugate toxic to resistant tumor cells
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The recent discovery that the formaldehyde conjugates of doxorubicin and daunorubicin, Doxoform and Daunoform, are cytotoxic to resistant human breast cancer cells prompted the search for hydrolytically more stable anthracycline-formaldehyde conjugates. Doxoform and Daunoform consist of two molecules of the parent drug bound together with three methylene groups, two forming oxazolidine rings and one binding the oxazolidines together at their 3'amino nitrogens. The 4'-epimer of doxorubicin, epidoxorubicin, reacts with formaldehyde at its amino alcohol functionality to produce a conjugate, Epidoxoform, in 59% yield whose structure consists of two molecules of epidoxorubicin bound together with three methylene groups in a 1,6-diaza- 4,9-dioxabicyclo[4.4.1]undecane ring system. The structure was established from spectroscopic data and is consistent with products from reaction of simpler vicinal trans-amino alcohols with formaldehyde. Epidoxoforrn hydrolyzes at pH 7.3 to an equilibrium mixture with dimeric and monomeric epidoxorubicin-formaldehyde conjugates without release of formaldehyde or epidoxorubicin. The hydrolysis follows the rate law (A mutually implies B) mutually implies C + D where A (Epidoxoform) is in rapid equilibrium with B, and B is in slow equilibrium with C and D. The forward rate constant for A/B going to C+D gives a half-life of approximately 2 h at 37 °C. At equilibrium the mixture is stable for at least 2 days. At pH 6.0, hydrolysis proceeds with first-order kinetics to epidoxorubicin and formaldehyde with a half- life of 15 min at 37 °C. Epidoxoform and epidoxorubicin plus formaldehyde react with the self-complementary DNA octamer (GC)4 to yield five drug-DNA adducts which have structures analogous to the doxorubicin-DNA adducts from reaction of Doxoform with (GC)4. Epidoxoform is 3-fold more toxic to MCF-7 human breast cancer cells and greater than 120-fold more toxic to MCF-7/ADR resistant cells than epidoxorubicin. Epidoxoform in equilibrium with its hydrolysis products is greater than 25-fold more toxic to resistant cells with respect to epidoxorubicin.
- Taatjes, Dylan J.,Fenick, David J.,Koch, Tad H.
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- The rate of homolysis of adducts of peroxynitrite to the C=O double bond
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Nucleophilic addition of the peroxynitrite anion, ONOO-, to the two prototypical carbonyl compounds, acetaldehyde and acetone, was investigated in the pH interval 7.4-14. The process is initiated by fast equilibration between the reactants and the corresponding tetrahedral adduct anion, the equilibrium being strongly shifted to the reactant side. The adduct anion also undergoes fast protonation by water and added buffers. Consequently, the rate of the bimolecular reaction between ONOO- and the carbonyl is strongly dependent on the pH and on the concentration of the buffer. The pKa of the carbonyl-ONOO adduct was estimated to be 11.8 and 12.3 for acetone and acetaldehyde, respectively. It is shown that both the anionic and the neutral adducts suffer fast homolysis along the weak O-O bond to yield free alkoxyl and nitrogen dioxide radicals. The yield of free radicals was determined to be about 15% with both carbonyl compounds at low and high pH, while the remainder collapses to molecular products in the solvent cage. The rate constants for the homolysis of the adducts vary from ca. 3 x 105 to ca. 5 x 106 s-1, suggesting that they cannot act as oxidants in biological systems. This small variation around a mean value of about 106 s-1 suggests that the O-O bond in the adduct is rather insensitive to its protonation state and to the nature of its carbonyl precursor. An overall reaction scheme was proposed, and all the corresponding rate constants were evaluated. Finally, thermokinetic considerations were employed to argue that the formation of dioxirane as an intermediate in the reaction of ONOO- with acetone is an unlikely process.
- Merenyi,Lind,Goldstein
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- Atmospheric sink of β-ocimene and camphene initiated by Cl atoms: Kinetics and products at NOx free-Air
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Rate coefficients for the gas-phase reactions of Cl atoms with β-ocimene and camphene were determined to be (in units of 10-10 cm3 per molecule per s) 5.5 ± 0.7 and 3.3 ± 0.4, respectively. The experiments were performed by the relative technique in an environmental chamber with FTIR detection of the reactants at 298 K and 760 torr. Product identification experiments were carried out by gas chromatography with mass spectrometry detection (GC-MS) using the solid-phase microextraction (SPME) method employing on-fiber carbonyl compound derivatization with o-(2,3,4,5,6-pentafluorobenzyl) hydroxylamine hydrochloride. An analysis of the available rates of addition of Cl atoms and OH radicals to the double bond of alkenes and cyclic and acyclic terpenes with a conjugated double bond at 298 K is presented. The atmospheric persistence of these compounds was calculated taking into account the measured rate coefficients. In addition, tropospheric chemical mechanisms for the title reactions are postulated.
- Gaona-Colmán, Elizabeth,Blanco, María B.,Barnes, Ian,Wiesen, Peter,Teruel, Mariano A.
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- Kinetics of the Reaction of Vinyl Radical with Molecular Oxygen
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The kinetics of the reaction C2H3 + O2 -> products (reaction 1) has been studied at temperatures 299-1005 K and He densities (3-18)E16 molecule cm-3 using laser photolysis/photoionization mass spectrometry.Rate constants were determined in time-resolved experiments as a function of temperature and bath gas density.The overall rate constant of reaction 1 is independent of pressure within the experimental range and can be described by the Arrhenius expression k1 = (6.92 +/- 0.17)E-12 exp(120 +/- 12 K)/T) cm3 molecule-1 s-1.Experimental results are compared with theoretical predictions, and implications for the mechanism of reaction 1 are discussed.
- Knyazev, Vadim D.,Slagle, Irene R.
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- O(1D) reaction with cyclopropane: Evidence of O atom insertion into the C-C bond
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The reaction kinetics of O(1D) with cyclopropane was investigated using the universal crossed molecular beam method. The detailed dynamics of this reaction was explained from the analysis of time of flight spectra and angular distribution of th
- Shu, Jinian,Lin, Jim J.,Wang, Chia C.,Lee, Yuan T.,Yang, Xueming,Nguyen, Thanh Lam,Mebel, Alexander M.
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- Ab initio study on the unimolecular decomposition mechanisms and spectroscopic properties of CH3OF
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High-level ab initio calculations of the structure, vibrational frequencies, and NMR spectra of the recently isolated methyl hypofluorite, CH3OF, have been carried out. When electron correlation is included in the calculations (but not at the HF level), there is a very good agreement between the experimental and the theoretical IR and NMR spectra. Four different unimolecular decomposition pathways, all leading to CH2O and HF, were studied. Of these, two mechanisms, the synchronous single-step HF elimination and a two-step mechanism via the CH3O? and F? radicals, are predicted to be the most favorable, both having activation free energies of ca. 38 kcal mol-1 at GAUSSIAN 2. A theoretical analysis of the expected kinetic isotope effects between the competing pathways leads to a clear differentiation which can be used in experimental studies.
- Apeloig, Yitzhak,Albrecht, Karsten
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- The Retardation of Methanol Oxidation at a Platinum Electrode in an Acid Solution
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The rate retardation of the oxidation of methanol at the potential range of about 0.65-0.8 V vs. a reversible hydrogen electrode on a platinum electrode in 0.5 mol dm-3 H2SO4 was studied.The rate retardation of the overall oxidation was caused by that of the oxidation, Reaction D, not via COad.From the relationship among the rate of Reaction D, the COad coverage, and the potentials, three types of rate retardation were found out: Type 1-Reaction D is not accelerated by the potential, and the rate of the reaction is determined by the COad coverage and the methanol concentration.Type 2- the rate of Reaction D decreases at stationary COad coverages as the oxidation is prolonged.Type 3- the rate decreases at COad coverages close to the limiting value.It is proposed that Types 1 and 2 of the rate retardations take place when the adsorption of methanol molecules is rate-determining, and when the formaldehyde and formic acid formed from methanol are accumulated in the vicinity of the electrode, respectively.Type 3 of the rate retardation has been explained in a preceding paper in terms of the aggregate damaging effect of COad.
- Matsui, Hiroshi
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- Photoinduced bimolecular reactions in homogeneous [CH3ONO]n clusters
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The photodissociation of homogeneous methyl nitrite clusters, [CH3ONO]n with n≈400-1000, was investigated in a supersonic jet using excitation mainly at 365 nm, which corresponds to S0→S1 (nπ*) excitation in the monomer. Besides the two types of NO(X2II) photofragment distributions, a rotationally relaxed one (Trot to approximately 250 K) and a nonthermally `hot' one (〈J″〉 = 35.5) which result from the primary dissociation step CH3ONO→CH3O+NO of cluster-bound CH3ONO, we observed the products HNO-(X1A′) and H2CO(X1A1) by state-selected LIF spectroscopy. Their product-yield excitation spectra and their formation dependence on the backing pressure revealed that HNO and H2CO originate exclusively from cluster photodissociation and not from primary photodissociation of the monomer. The mechanism of their formation was found to be the disproportionation reaction of the primary photofragments, CH3O+NO→HNO+H2CO, mediated by caging of the cluster environment. The fragments collide with, and recoil at, the solvent shell followed by subsequent recombination, disproportionation, or escape from the evaporating solvent cage. The present results are consistent with previous findings on the photolysis of isolated CH3ONO molecules in solid noble gas matrices where exclusively the products HNO and H2CO were found.
- Bergmann,Huber
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- A kinetic study of the reactions of NO3 with methyl vinyl ketone, methacrolein, acrolein, methyl acrylate and methyl methacrylate
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Rate coefficients for the reactions NO3 + CH3C(O)CHCH2 → products(1), NO3 + CH2C(CH3)CHO → products(2), NO3 + CH2CHCHO → products, and NO3 + CH2CHC(O)OCH3 → products were obtained by relative and absolute methods. The rate coefficient for the reaction NO3 + CH2C(CH3)C(O)OCH3 → products was determined by the relative-rate method only. Relative rate measurements agreed with results of previous studies. However, in some cases, the kinetic data obtained using the absolute method were significantly higher than those from the relative technique which may be due to secondary chemistry and reactive impurities. Product studies revealed that methyl glyoxal is a product of reactions (1) and (2) along with peroxymethacryloyl nitrate for (2) in air. A diurnally varying boundary-layer model suggests that (2) is an important loss process for methacrolein, which can lead to OH generation at night. NO3 may be an important oxidant for methacrolein in the urban boundary layer and where urban plumes impact on forested areas.
- Wayne,Shallcross,Canosa-Mas,Carr,King,Thompson
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- Strong photon energy dependence of the photocatalytic dissociation rate of methanol on TiO2(110)
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Photocatalytic dissociation of methanol (CH3OH) on a TiO 2(110) surface has been studied by temperature programmed desorption (TPD) at 355 and 266 nm. Primary dissociation products, CH2O and H atoms, have been detected. Th
- Xu, Chengbiao,Yang, Wenshao,Ren, Zefeng,Dai, Dongxu,Guo, Qing,Minton, Timothy K.,Yang, Xueming
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- Infrared Matrix Isolation Studies of the Reactions of Dichloro- and Dibromomethane with Atomic Oxygen
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The reactions of atomic oxygen with CH2Cl2 and CH2Br2 trapped in argon matrices have been studied by FTIR spectroscopy.O(1D) and O(3P) were generated in situ by UV photolysis of co-deposited ozone.Products were identified by employing 18O and scrambled 18O/16O ozone as well as deuterated methylene halides.Kinetic studies performed on both CH2Cl2 and CH2Br2 with O(1D) under the same experimental conditions allowed the reaction pathway to be determined.With CH2Br2 as parent molecule, three routes were evident leading to (i) CHOBr,(ii) CO...(HBr)2, and (iii) CH2O.With CH2Cl2 as parent molecule, only the first two channels were observed.Carbonyl compounds rapidly decomposed under irradiation, and CO...(HX)2 was also produced as a secondary species.
- Lugez, C.,Schriver, A.,Schriver-Mazzuoli, L.,Lasson, E.,Nielsen, C. J.
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- Absorption Cross Section and Kinetics of IO in the Photolysis of CH3I in the Presence of Ozone
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The photolysis of CH3I in the presence of O3 was used as a source of IO radicals in N2 + O2 diluent at 1-atm pressure and 303 K.IO was detected in absorption by using the molecular modulation technique.The absorption spectrum in the region 415-470 nm, arising from the A2Π 2Π transition of IO, was recorded and the absolute absorption cross section at the band head of the (4-0) band at 426.9 nm determined to be 3.1+2.0-1.5x10-17 cm2 molecule-1.IO decayed by a rapid reaction which yielded an aerosol of probable formula I4O9 as a final product.The observed rate coefficient for IO decay was near the gas kinetic collision rate which probably reflects an efficient attachment of IO radicals to the growing aerosol.The significance of the photochemical and kinetic parameters for atmospheric iodine chemistry is briefly discussed.
- Cox, R. A.,Coker, G. B.
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- Nonenforced Concerted General-Acid Catalysis of the Dehydration Step in Formaldehyde Thiosemicarbazone Formation
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At pH>6 the formation of formaldehyde thiosemicarbazone proceeds with rate-limiting dehydration of the carbinolamine intermediate, which is at equilibrium with formaldehyde hydrate and thiosemicarbazide (K = 550 M-1).At higher concentrations of formaldehyde a bis(formaldehyde) addition compound is formed, which undergoes dehydration more slowly.The dehydration step is subject to general-acid catalysis by phosphate and phosphonate buffers with α = 0.83.A solvent deuterium isotope effect of kHA/kDA = 2.6 for catalysis by ethylphosphonate monoanion and published evidence support a concerted mechanism of catalysis.The calculated rate constant for formation of the O-protonated carbinolamine is > 104 faster than the observed rate constant for dehydration and the rate constant for expulsion of water from this species is 7 s-1.Thus, it appears that a concerted mechanism can exist when it is not enforced by the nonexistence of the O-protonated species.The secondary α-deuterium isotope effect of KH/kD = 1.06 (1.03 /D) for catalysis by phosphate monoanion suggests an early transition state but other criteria suggest a central or late transition state for C-O cleavage.
- Palmer, John L.,Jencks, William P.
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- Direct kinetics study of the temperature dependence of the CH2O branching channel for the CH3O2 + HO2 reaction
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A direct kinetics study of the temperature dependence of the CH2O branching channel for the CH3O2 + HO2 reaction has been performed using the turbulent flow technique with high-pressure chemical ionization mass spectrometry for the detection of reactants and products. The temperature dependence of the CH2O-producing channel rate constant was investigated between 298 and 218 K at a pressure of 100 Torr, and the data were fitted to the following Arrhenius expression. 1.6-0.7+1.0 × 10-15 × exp[(1730 ± 130)/T] cm3 molecule-1 s-1. Using the Arrhenius expression for the overall rate of the CH3O2 + HO2 reaction and this result, the 298 K branching ratio for the CH2O producing channel is measured to be 0.11, and the branching ratio is calculated to increase to a value of 0.31 at 218 K, the lowest temperature accessed in this study. The results are compared to the analogous CH3O2 + CH3O2 reaction and the potential atmospheric ramifications of significant CH2O production from the CH3O2 + HO2 reaction are discussed.
- Elrod, Matthew J.,Ranschaert, Dana L.,Schneider, Nicholas J.
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- BIOSYNTHESIS OF DOLICHOLACTONE IN TEUCRIUM MARUM
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Iridodial is a very efficient precursor of dolicholactone in Teucrium marum.In the biogenetic formation of the lactone ring a hydride shift from C-1 to C-10 is observed.Citronellol and its 10-hydroxy derivative are preferred as precursors with respect to the C-2/C-3 unsaturated analogues. - Key Word Index: Teucrium marum; Labiate; dolicholactone; monoterpene biosynthesis; iridane skeleton; hydride shift.
- Grandi, Romano,Pagnoni, Ugo M.,Pinetti, Adriano,Trave, Roberto
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- Formaldehyde Production by Tris Buffer in Peptide Formulations at Elevated Temperature
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This technical note provides evidence for the degradation of Tris buffer in apeptide formulation stored at elevated temperature (70 deg C). The buffer degrades to liberate formaldehyde, which is shown to react with the peptide tyrosine residue. Those invo
- Song, Yuan,Schowen, Richard L.,Borchardt, Ronald T.,Topp, Elizabeth M.
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- Mechanistic and kinetic study of formaldehyde production in the atmospheric oxidation of dimethyl sulfide
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Tunable diode laser spectroscopic detection of formaldehyde (H2CO) and HCl coupled with laser flash photolysis of Cl2CO-CH3SCH3-O2-N2 mixtures, in both the presence and absence of NO, has been utilized to conduct a mechanistic and kinetic investigation of the atmospheric oxidation of the CH3SCH2 radical, a product of dimethyl sulfide (DMS, CH3SCH3) reactions with OH and NO3 in the atmosphere. The temperature dependence of the CH3SCH2O2 + NO rate coefficient (k2) and the 298 K rate coefficient for the CH3SCH2O2 self reaction (k4) have been measured. The Arrhenius expression k2 = 4.9 × 10-12 exp(263/T) cm3 molecule-1 s-1 adequately summarizes our CH3SCH2O2 + NO kinetic data over the temperature range 261-400 K. Contributions from side reactions, which are not completely quantifiable, limit the accuracy of the k4 (298 K) determination; our results indicate that the true value for this rate coefficient is within the range (1.2 ± 0.5) × 10-11 cm3 molecule-1 s-1. In both reactions CH3SCH2O2 is converted to H2CO with unit yield (at T = 298 K). Our results demonstrate that the lifetime of CH3SCH2O, a proposed precursor to H2CO, is less than 30 μs at 261 K and 10 Torr total pressure.
- Urbanski, Shawn P.,Stickel, Robert E.,Zhao, Zhizhong,Wine, Paul H.
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- Rections Of CH2OO and CH2(1A1) with H2O in the Gas Phase
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The reactions of peroxymethylene (CH2OO) and singlet methylene with H2O were studied in the gas phase by near-UV photolysis of ketene and diazomethane.Peroxymethylene formed in the reaction of CH2(3B1) + O2 + M----> CH2OO + M was found to react with H2(18)O to produce labeled formic acid: CH2OO + H2(18)O ---> HC(18)OOH + H2O.Singlet Methylene was found to react with H2O to form methanol, CH2(1A1) + H2O ---> CH3OH, competing with the reactiom CH2(1A1) + CH2N2 ---> C2H4 + N2.
- Hatakeyama,Shiro,Bandow, Hiroshi,Okuda, Michio,Akimoto, Hajime
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- Electro-Assisted Reduction of CO2 to CO and Formaldehyde by (TOA)6[α-SiW11O39Co(-)] Polyoxometalate
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We report here on the multiproton-multielectron electrochemical reduction of CO2 in homogeneous solution by using (TOA)6[α-SiW11O39Co(-)] (TOA = tetraoctyl ammonium; - = vacant position in the coordination sphere of Co) as an electrocatalyst. First, the electrochemical behavior of (TOA)6[α-SiW11O39Co(-)] was analyzed in detail by cyclic voltammetry in dichloromethane, studying the influence of the presence of protons and/or CO2. These preliminary results were further used to optimize the conditions of electrolysis in terms of reduction potentials. Analysis of the electrolysis products in the gas and liquid phases show the formation of CO and HCHO without formation of H2. Our results tend to show that the (TOA)6[α-SiW11O39Co(-)] polyoxometalate is a catalyst for CO2 electroreduction, with unique selectivity. The cobalt derivative of the silico-undecatungstate [α-SiW11O39Co(-)]6- is a catalyst for the multiproton-multielectron electrochemical reduction of CO2, with unique selectivity.
- Girardi, Marcelo,Blanchard, Sbastien,Griveau, Sophie,Simon, Philippe,Fontecave, Marc,Bedioui, Fethi,Proust, Anna
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- New alkyl-cobalt(III) complexes with tridentate amino-oxime ligands: Synthesis, structure, and reactivity
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The oxidative addition of alkyl halides to the CoI species generated by the reduction of [CoIII(LNHpy)(HLNHpy)]-(ClO4)2 (1), where HLNHpy is the tridentate 2-(2-pyridyl-ethyl)amino-3-butanone oxime ligand and LNHpy is its conjugate base, led to the formation of a new class of organocobalt complexes of general formula [RCoIII(LNHpy)(HLNHpy)]-(ClO4) [R = Me (2a), Et (2b), CH2CF3 (2c), nBu (2d), and CH2Cl (2e)]. All the complexes were characterised by 1H and 13C NMR spectroscopy. The X-ray structures of 2a, 2b and 2c provide evidence for a pseudo-octahedral configuration, where HLNHpy and LNHpy act as bi- and tridentate ligands, respectively. The axial geometry in 2a is closer to that found in methylcobalamin than that reported for other models, suggesting steric and electronic cis influences of the equatorial ligands close to those of the corrin nucleus. The solution properties and the reactivity show strong analogies with those of the previously known Vitamin B12 models.
- Dreos, Renata,Felluga, Alessandro,Nardin, Giorgio,Randaccio, Lucio,Siega, Patrizia,Tauzher, Giovanni
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- Carboxylation of methane with CO or CO2 in aqueous solution catalysed by vanadium complexes
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Reaction of methane with CO or CO2 in aqueous solution in the presence of O2 (catalysed by NaVO3) or H2O2 (catalysed by NaVO3-pyrazine-2-carboxylic acid) at 25-100 °C affords acetic acid and in some cases also methanol, methyl hydroperoxide and formaldehyde.
- Nizova, Galina V.,Suess-Fink, Georg,Stanislas, Sandrine,Shul'Pin, Georgiy B.
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- Catalytic Oxidation of Methane to Methanol initiated in a Gas Mixture of Hydrogen and Oxygen
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Selective oxidation of methane to methanol at atmospheric pressure has been achieved using a gas mixture of hydrogen and oxygen over iron phosphate catalyst at > 623 K.
- Wang, Ye,Otsuka, Kiyoshi
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- The BODIPY-Based Chemosensor for Fluorometric/Colorimetric Dual Channel Detection of RDX and PA
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A fluorometric/colorimetric dual-channel chemosensor based on a hydrazine-substituted BODIPY probe has been successfully fabricated for the detection of RDX and PA. The chemosensor displays turn-on fluorescence behavior upon RDX with a detection limit of 85.8 nM, while showing a turn-off response to PA with a detection limit of 0.44 μM. Meanwhile, an obvious color difference is observed by the naked-eye after the reaction for RDX. Thus, in application, a two-to-two logic gate is constructed for potential application in explosives detection. Additionally, portable equipment is also developed for in situ determination of RDX.
- Gao, Jianmei,Chen, Xiaoxiao,Chen, Shuqin,Meng, Hu,Wang, Yu,Li, Chunsheng,Feng, Liang
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- Kinetics of the Reaction between Methoxyl Radicals and Hydrogen Atoms
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The kinetics of the reaction of CH3O with H have been studied under pseudo-first-order conditions with an excess of H using an isothermal discharge-flow reactor.Three different CH3O sources were used and the decay of was monitored by laser-induced fluorescence (LIF) as a function of .A second-order rate coefficient of (2.0 +/- 0.6) x 1013 cm3 mol-1 s-1 was determined for reaction CH3O + H -> products at room temperature and a slight positive temperature dependence was observed between 298 and 490 K.Formaldehyde formation was found to be the dominant reaction path (81 +/- 12percent).Further identified products were OH (7 +/- 3percent) and methanol (a few percent) which were produced by the decomposition and stabilization, respectively, of the initially formed bound adduct.
- Dobe, Sandor,Berces, Tibor,Szilagyi, Istvan
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- 44-Methylgambierone, a new gambierone analogue isolated from Gambierdiscus australes
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A new analogue of gambierone, 44-methylgambierone, was isolated from the benthic dinoflagellate Gambierdiscus australes collected from Raoul Island (Rangitahua/Kermadec Islands). This molecule has been previously reported as maitotoxin-3. The structure of 44-methylgambierone was elucidated using 1D- and 2D-nuclear magnetic resonance spectroscopy and mass spectrometry techniques. The nine-ring polyether backbone (A–I) and functional groups (carbonyl, terminal diol, 1,3-diene and monosulphate) are the same for both compounds with the addition of an olefinic methyl group being the only modification in 44-methylgambierone.
- Murray, J. Sam,Selwood, Andrew I.,Harwood, D. Tim,van Ginkel, Roel,Puddick, Jonathan,Rhodes, Lesley L.,Rise, Frode,Wilkins, Alistair L.
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- Oxidation of triethanolamine by ceric ammonium sulfate in aqueous sulfuric acid: spectrophotometric kinetic and mechanistic study
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Oxidation kinetics of triethanolamine by ceric ammonium sulfate in aqueous sulfuric acid has been studied spectrophotometrically in contexts of many physicochemical processes. Stoichiometry of the reaction is found to be 1:6. Contrary to the literature findings the reaction proceeds without the presence of any transition metals acting as catalysts. Oxidation kinetics shows unit order dependence on oxidant, Ce(IV) and substrate, triethanolamine as well. Complex, fractional inverse order dependence on [H+], unaltered rate in the presence of added products at the initial stage and inverse dependence on added salt, sodium bisulfate are the findings. With increase in the solvent polarity, rate of the reaction also increased. Activation and thermodynamic parameters are computed from the temperature dependence observations. Suitable kinetic model and explanations are provided considering all the findings with a proposal of formation of an activated complex of the type [Ce(IV)-triethanolamine]. Graphical abstract: [Figure not available: see fulltext.]
- Padhy, Ranjan Kumar,Sahu, Sarita
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- Highly selective oxidation of methane to formaldehyde on tungsten trioxide by lattice oxygen
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Photocatalytic oxidation of methane into formaldehyde in high yield and selectivity remains a grand challenge due to the ineluctable intermediates. Here, we report that a {001}, {010} and {100} facets modified tungsten trioxide photocatalyst enables an intermediate-free oxidation of methane into formaldehyde with 99.4% selectivity. A durable formaldehyde yield of 4.61 mmol g?1 can be achieved after irradiation for 30 h. Mechanism studies disclose that surface defect and reactive lattice oxygen atom are crucial for the selectivity and productivity promotion. This work provides a valid paradigm for efficient conversion of methane to formaldehyde.
- Fan, Yingying,Han, Dongxue,Jiang, Yuheng,Lu, Rongxia,Niu, Li,Pan, Guoliang,Wang, Wei,Wei, Shilei,Zhang, Peiyun,Zhu, Xianglian
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- Method for preparing formaldehyde by photocatalytic oxidation of ethylene glycol
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The invention provides a method for preparing formaldehyde from ethylene glycol by photocatalytic oxidation. According to the method, ethylene glycol is taken as a substrate, air or oxygen is taken asan oxygen source, and a C-C bond cracked product, namely, formaldehyde can be generated under illumination in presence of a catalyst. The conditions are mild, the oxidation efficiency and the productyield are high, and the air or the oxygen is taken as the oxygen source under the illumination condition, so that the method is economical, environmentally friendly and green, meets the strategy of sustainable developed energy and has broad application prospect.
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Paragraph 0007; 0033-0080
(2021/05/26)
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- Unprecedentedly high efficiency for photocatalytic conversion of methane to methanol over Au-Pd/TiO2-what is the role of each component in the system?
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Direct and highly efficient conversion of methane to methanol under mild conditions still remains a great challenge. Here, we report that Au-Pd/TiO2 could directly catalyze the conversion of methane to methanol with an unprecedentedly high methanol yield of 12.6 mmol gcat-1 in a one-hour photocatalytic reaction in the presence of oxygen and water. Such an impressive efficiency is contributed by several factors, including the affinity between Au-Pd nanoparticles and intermediate species, the photothermal effect induced by visible light absorption of Au-Pd nanoparticles, the employment of O2 as a mild oxidant, and the effective dissolution of methanol in water. More importantly, for the first time, thermo-photo catalysis is demonstrated by the distinct roles of light. Namely, UV light is absorbed by TiO2 to excite charge carriers, while visible light is absorbed by Au-Pd nanoparticles to increase the temperature of the catalyst, which further enhances the driving force of corresponding redox reactions. These results not only provide a valuable guide for designing a photocatalytic system to realize highly efficient production of methanol, but also, highlight the great promise of thermo-photo catalysis. This journal is
- Cai, Xiaojiao,Fang, Siyuan,Hu, Yun Hang
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supporting information
p. 10796 - 10802
(2021/05/14)
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- High catalytic methane oxidation activity of monocationic μ-nitrido-bridged iron phthalocyanine dimer with sixteen methyl groups
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Herein, we report the highly potent catalytic methane oxidation activity of a monocationic μ-nitrido-bridged iron phthalocyanine dimer with 16 peripheral methyl groups. It was confirmed that this complex oxidized methane stably into MeOH, HCHO, and HCOOH in a catalytic manner in an acidic aqueous solution containing excess H2O2 at 60 °C. The total turnover number of the reaction reached 135 after 12 h, which is almost seven times higher than that of a monocatinoic μ-nitrido-bridged iron phthalocyanine dimer with no peripheral substituents. This suggests that the increased number of peripheral electron-donating substituents could have facilitated the generation of a reactive high-valent iron-oxo species as well as hydrogen abstraction from methane by the reactive iron-oxo species.
- Kura, Jyunichi,Tanaka, Kentaro,Toyoda, Yuka,Yamada, Yasuyuki
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supporting information
p. 6718 - 6724
(2021/05/26)
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- Enhancement and limits of the selective oxidation of methane to formaldehyde over V-SBA-15: Influence of water cofeed and product decomposition
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The possibility of a selective catalytic oxidation of methane to formaldehyde has been known for decades, and positive influences of water added to the reaction mixture and ultra-short contact times have been reported. In the present work, the complexity of interdependencies has been revealed. Specific parameter variations can increase conversion and selectivity of the target product. Surprisingly, formaldehyde formation over VOx species and its decomposition in gas phase were equally dependent on the partial pressure of the added water, so that the sweet spot can only be found by varying the residence time.
- Kunkel, Benny,Wohlrab, Sebastian
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- Study on the selective oxidation of methane over highly dispersed molybdenum-incorporated KIT-6 catalysts
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A series of molybdenum-incorporated mesoporous silica (Mo-KIT-6) catalysts were successfully synthesized by a one-pot hydrothermal synthesis method, and were applied in the selective oxidation of methane to formaldehyde using oxygen as an oxidizing agent under atmospheric pressure. Comparatively, the corresponding supported catalysts (Mo/KIT-6) were prepared by incipient-wetness-impregnation method. The results of the small angle XRD, nitrogen adsorption/desorption isotherms, UV-vis, H2-TPR and UV-Raman spectroscopy characterization combined with the catalytic activity tests demonstrated that molybdenum atoms were inserted into the framework of the mesoporous materials for the Mo-KIT-6 catalysts and the highly dispersed MoO bonds dominantly existed, which were responsible for the efficient selective formation of formaldehyde. However, for Mo/KIT-6 catalysts, the molybdenum oxide species were mainly loaded on the surface or inside the outer pore channels of the support and abundant emergence of the Mo-O-Mo bond played a major role in the activation of methane to COx. Furthermore, with equivalent molybdenum content, the methane selective oxidation performance of 8Mo-KIT-6 was obviously better than that of 4.6Mo/KIT-6, and the formaldehyde yield (2.1%) of 8Mo-KIT-6 was 2.3 times as much as that (0.9%) of 4.6Mo/KIT-6.In situandoperandoUV-Raman results demonstrated that the structures of the MoOxactive sites have a strong effect on the formation and elimination of carbon deposition during the separated redox reaction with methane and O2, respectively. The polymerized MoOxactive sites are favorable for the formation of graphitic carbon (G), which is called ordered carbon, while the isolated MoOxactive sites are favorable for the formation of disordered carbon (D). The reduced highly dispersed MoOxactive sites incorporated in the framework of silica are more easily reoxidized than those on the supported catalysts.
- Chen, Pei,Fan, Xiaoqiang,Kong, Lian,Li, Jianmei,Liu, Baijun,Liu, Bonan,Xiao, Xia,Xie, Zean,Zhao, Zhen
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p. 4083 - 4097
(2021/06/30)
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- Iron phosphate nanoparticle catalyst for direct oxidation of methane into formaldehyde: Effect of surface redox and acid-base properties
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The effect of various iron phosphate and oxide catalysts on the direct oxidation of methane (CH4) to formaldehyde (HCHO) with molecular oxygen (O2) as the sole oxidant was studied using a fixed-bed flow reactor. Five crystalline iron-containing catalysts (FePO4, Fe3O3(PO4), Fe4(P2O7)3, Fe2P2O7, and α-Fe2O3) with different iron coordination geometries, iron oxidation states, and Fe/P ratios were synthesized by the sol-gel method using malic acid or aspartic acid. The Fe/P molar ratio had a significant effect on the oxidation catalysis; CH4 conversion increased with the Fe/P molar ratio, although the selectivity to HCHO decreased. Trigonal FePO4 nanoparticles synthesized by the malic acid-aided method with an Fe/P molar ratio of 1/1 exhibited the highest activity for the selective formation of HCHO among the catalysts tested, including FePO4 synthesized by a conventional method. Despite the much higher oxidizing ability of Fe2O3 than FePO4, the oxidation of CH4 using Fe2O3 resulted in the formation of only CO2. In contrast, the temperature-programmed reaction of FePO4 with CH4 gave Fe2P2O7 with the formation of HCHO as a primary product, and Fe2P2O7 reacted with O2 to regenerate FePO4. Based on mechanistic studies including the catalyst effect, kinetics, pulse-reaction experiments, and IR spectroscopy, the bulk structural change between FePO4 and Fe2P2O7 is not involved during the catalysis and the surface redox and acid-base properties of FePO4 are considered to play an important role in CH4 oxidation with the structure preservation of bulk FePO4. The combination of redox-active Lewis acidic iron sites and weakly-basic phosphate units likely contributes to the C-H activation of CH4 and the suppression of complete oxidation to CO2, respectively.
- Hara, Michikazu,Kamata, Keigo,Matsuda, Aoi,Tateno, Haruka
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p. 6987 - 6998
(2021/11/13)
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- A nonheme peroxo-diiron(iii) complex exhibiting both nucleophilic and electrophilic oxidation of organic substrates
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The complex [FeIII2(μ-O2)(L3)4(S)2]4+(L3= 2-(4-thiazolyl)benzimidazole, S = solvent) forms upon reaction of [FeII(L3)2] with H2O2and is a functional model of peroxo-diiron intermediates invoked during the catalytic cycle of oxidoreductases. The spectroscopic properties of the complex are in line with those of complexes formed with N-donor ligands. [FeIII2(μ-O2)(L3)4(S)2]4+shows both nucleophilic (aldehydes) and electrophilic (phenol,N,N-dimethylanilines) oxidative reactivity and unusually also electron transfer oxidation.
- Browne, Wesley R.,Giorgi, Michel,Kaizer, József,T?r?k, Patrik,Unjaroen, Duenpen,Viktória Csendes, Flóra
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supporting information
p. 7181 - 7185
(2021/06/11)
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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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- Oxidation of methane to methanol over Pd@Pt nanoparticles under mild conditions in water
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Direct methane oxidation into oxygen-containing chemicals under mild conditions has sparked increasing interest. Here, we report Pd@Pt core-shell nanoparticles that efficiently catalyse the direct oxidation of CH4to CH3OH in water using H2O2as an oxidant under mild conditions. The catalyst presents a methanol productivity of up to 89.3 mol kgcatalyst?1h?1with a high selectivity of 92.4% after 30 min at 50 °C, thus outperforming most of the previously reported catalysts. Electron-enriched Pt species in the Pd@Pt nanoparticles were identified by structural and electronic analysis. Pd in the core donates electrons to Pt, leading to higher rates of methane activation. Based on the results of control experiments and kinetic analysis, a consecutive oxidation pathwayviaa radical mechanism is proposed, which includes initial formation of CH3OOH and CH3OH followed by further oxidation of CH3OH to HCHO, HCOOH, and CO2
- Chen, Jianjun,Chen, Yaoqiang,Collière, Vincent,Lecante, Pierre,Peres, Laurent,Philippot, Karine,Wang, Sikai,Yan, Ning
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p. 3493 - 3500
(2021/06/06)
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- Ternary ZnO/CuO/Zeolite composite obtained from volcanic ash for photocatalytic CO2 reduction and H2O decomposition
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An n-p heterojunction based on ZnO/CuO supported in a zeolitic framework (ZF) was designed to produce solar fuels from H2O decomposition and CO2 conversion. ZF was synthesized from volcanic ashes by an alternative microwave-hydrothermal method using a biodegradable template for its formation. The framework resulted in NaAlSiO4 (NAS) with a high surface area and a morphology composed of circular channels of 50 nm. Incorporating the ZnO/CuO heterostructure in the NAS channels resulted in an improved light-absorption, more efficient charge transfer, nanostructure morphology, and more active sites available for the CO2 adsorption and photocatalytic reactions. The activities for H2 and light-hydrocarbons (HCOOH, HCOH, and CH3OH) evolution were evaluated in the photocatalytic water-splitting and CO2 reduction under UVA irradiation, respectively. The ZnO/CuO/NAS composite exhibited a remarkably higher H2 (187 μmol/g) and HCOOH (2721 μmol/g) evolution after 3 h of irradiation. These results were related to the synergistic effect among ZnO, CuO, and NAS framework. A mechanism of the photocatalytic reaction was proposed.
- Luévano-Hipólito,Torres-Martínez, Leticia M.,Fernández-Trujillo
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- Enhanced CO2 Conversion into Ethanol by Permanently Polarized Hydroxyapatite through C?C Coupling
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Hydroxyapatite (HAp) is a naturally occurring mineral form of calcium apatite of biomedical importance due to its similarity with human hard tissues in morphology and composition. Upon polarization at high temperature, applying 3 kV/cm at 1000 °C, the resulting polarized HAp (p-HAp) exhibits enhanced catalytic behavior due charge accumulation at the interface. More specifically, p-HAp was found to catalyse the conversion of mixtures of CO2(g) and CH4(g) into low carbon organic molecules and into amino acids when N2(g) was added to the mixture. In this work, we report how p-HAp facilitates the conversion of CO2(g) mainly in ethanol by means of forming C?C coupled bonds on its activated surface. After evaluation of a wide range of experimental conditions, we evidence the production of formic acid, methanol and formaldehyde (C1 products); ethanol and acetic acid (C2 products); and acetone (C3 product) from CO2(g) using moderate reaction conditions. Moreover, optimization of the reaction parameters led to a significant increase towards ethanol.
- Sans, Jordi,Sanz, Vanesa,Turon, Pau,Alemán, Carlos
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p. 5025 - 5033
(2021/10/29)
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- PROCESSES FOR PREPARING C-4 SUGARS AND KETOSE SUGARS
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Various processes for preparing C4 aldoses and/or ketones thereof are described. Various processes are described for preparing C4 aldoses and/or ketones thereof from feed compositions comprising glycolaldehyde. Also, various processes for preparing useful downstream products and intermediates, such as erythritol and erythronic acid, from the C4 aldoses and/or ketones thereof are described.
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Page/Page column 19-21; 35-36
(2021/11/20)
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- PROCESSES FOR THE PYROLYSIS OF CARBOHYDRATES
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Various processes for the pyrolysis of carbohydrates to prepare products such as glycolaldehyde are described. Also, various catalysts and processes for preparing catalysts useful for carbohydrate pyrolysis are described.
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Page/Page column 13-15; 27-28
(2021/11/20)
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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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- Effect of relative percentage of acid and base sites on the side-chain alkylation of toluene with methanol
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K3PO4/NaX catalysts were prepared by loading potassium phosphate on NaX zeolite, and the catalytic performance was studied for the side-chain alkylation of toluene with methanol to styrene and ethylbenzene. Combined with the characte
- Li, Huijun,Wang, Bin,Wen, Yueli,Hao, Chunyao,Liu, Yuhua,Huang, Wei
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p. 12703 - 12709
(2021/04/14)
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- Selective Reductive Dimerization of CO2into Glycolaldehyde
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The selective dimerization of CO2 into glycolaldehyde is achieved in a one-pot two-step process via formaldehyde as a key intermediate. The first step concerns the iron-catalyzed selective reduction of CO2 into formaldehyde via formation and controlled hydrolysis of a bis(boryl)acetal compound. The second step concerns the carbene-catalyzed C-C bond formation to afford glycolaldehyde. Both carbon atoms of glycolaldehyde arise from CO2 as proven by the labeling experiment with 13CO2. This hybrid organometallic/organic catalytic system employs mild conditions (1 atm of CO2, 25 to 80 °C in less than 3 h) and low catalytic loadings (1 and 2.5%, respectively). Glycolaldehyde is obtained in 53% overall yield. The appealing reactivity of glycolaldehyde is exemplified (i) in a dimerization process leading to C4 aldose compounds and (ii) in a tri-component Petasis-Borono-Mannich reaction generating C-N and C-C bonds in one process.
- Zhang, Dan,Jarava-Barrera, Carlos,Bontemps, Sébastien
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p. 4568 - 4575
(2021/05/04)
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- Four-Selective Pyridine Alkylation via Wittig Olefination of Dearomatized Pyridylphosphonium Ylides
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Methods to synthesize alkylated pyridines are valuable because these structures are prevalent in pharmaceuticals and agrochemicals. We have developed a distinct approach to construct 4-alkylpyridines using dearomatized pyridylphosphonium ylide intermediates in a Wittig olefination-rearomatization sequence. Pyridine N-activation is key to this strategy, and N-triazinylpyridinium salts enable coupling between a wide variety of substituted pyridines and aldehydes. The alkylation protocol is viable for late-stage functionalization, including methylation of pyridine-containing drugs. This approach represents an alternative to metal-catalyzed sp2-sp3 cross-coupling reactions and Minisci-type processes.
- Dolewski, Ryan D.,Fricke, Patrick J.,McNally, Andrew
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supporting information
p. 21283 - 21288
(2021/08/25)
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- Enantioselective Reductive Oligomerization of Carbon Dioxide into l-Erythrulose via a Chemoenzymatic Catalysis
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A cell-free enantioselective transformation of the carbon atom of CO2has never been reported. In the urgent context of transforming CO2into products of high value, the enantiocontrolled synthesis of chiral compounds from CO2would be highly desirable. Using an original hybrid chemoenzymatic catalytic process, we report herein the reductive oligomerization of CO2into C3(dihydroxyacetone, DHA) and C4(l-erythrulose) carbohydrates, with perfect enantioselectivity of the latter chiral product. This was achieved with the key intermediacy of formaldehyde. CO2is first reduced selectively by 4e-by an iron-catalyzed hydroboration reaction, leading to the isolation and complete characterization of a new bis(boryl)acetal compound derived from dimesitylborane. In an aqueous buffer solution at 30 °C, this compound readily releases formaldehyde, which is then involved in selective enzymatic transformations, giving rise either (i) to DHA using a formolase (FLS) catalysis or (ii) to l-erythrulose with a cascade reaction combining FLS and d-fructose-6-phosphate aldolase (FSA) A129S variant. Finally, the nature of the synthesized products is noteworthy, since carbohydrates are of high interest for the chemical and pharmaceutical industries. The present results prove that the cell-freede novosynthesis of carbohydrates from CO2as a sustainable carbon source is a possible alternative pathway in addition to the intensely studied biomass extraction andde novosyntheses from fossil resources.
- Bontemps, Sébastien,Clapés, Pere,Desmons, Sarah,Dumon, Claire,Fauré, Régis,Grayson-Steel, Katie,Hurtado, John,Nu?ez-Dallos, Nelson,Vendier, Laure
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supporting information
p. 16274 - 16283
(2021/10/12)
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- Trapped copper in [6]cycloparaphenylene: A fully-exposed Cu7single cluster for highly active and selective CO electro-reduction
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The present work introduces a new single cluster catalyst consisting of loop-like [6]cycloparaphenylene ([6]CPP) as the support and an exposed central hexagonal-shaped Cu7 cluster as the metal center. DFT calculations prove that, originating from the mixed charge state and resultant synergistic effect of Cu atoms, Cu7@[6]CPP can be utilized as a highly active and selective catalyst for the electro-reduction of CO to produce formaldehyde.
- Dang, Jing-Shuang,Liu, Yi-Qing,Qiu, Zi-Yang,Wang, Wei-Wei,Zhao, Xiang
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supporting information
p. 25922 - 25926
(2021/12/13)
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- Method for preparing aldehyde/ketone by breaking C-C key
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The invention discloses a method for preparing aldehyde/ketone by breaking C-C bonds, and the method comprises the following steps of anaerobic condition. In an organic solvent system, an alcohol is used as a reaction raw material, and the C-C bond is selectively broken under the common action of an iron catalyst, an organic base and an additive to obtain aldehyde/ketone. The method is low in cost, easy to obtain, wide in substrate range, simple and product in post-treatment and high in purity, a new synthetic route and a method are developed for an aldehyde ketone compound, and the method has good application potential and research value.
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Paragraph 0113-0118
(2021/11/19)
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- Lanthanum modified Fe-ZSM-5 zeolites for selective methane oxidation with H2O2
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Selective partial oxidation of methane to methanol under ambient conditions is a great challenge in chemistry. Iron modified ZSM-5 catalysts are shown to be effective for this reaction using H2O2as the oxidant. However, the high consumption of H2O2over this catalyst presents a major disadvantage. Here we report a lanthanum modified Fe-ZSM-5 (LaFe-ZSM-5) catalyst for enhanced selective methane oxidation with suppressed H2O2consumption. Using 0.5 wt% LaFe-ZSM-5 pretreated with H2the productivity of primary oxygenated products (CH3OH, CH3OOH, HCOOH) is 3200 mol kgLaFe?1h?1in 0.1 M H2O2, with a selectivity of 98.9% to primary oxygenated products. The productivity is increased to 11?460 mol kgLaFe?1h?1in 0.5 M H2O2. Compared with Fe-ZSM-5, LaFe-ZSM-5 uses 31% less H2O2for obtaining per mol of product under the same conditions.In situDRIFT spectroscopy and solid state MAS NMR revealed the high H2O2consumption in ZSM-5 based catalyst maybe closely related to the acidity of strong Br?nsted acid sites (Si(OH)Al). The La modified ZSM-5 catalyst can decrease the acidity of the strong Br?nsted acid sites and this suppresses the decomposition of H2O2
- Barnes, Alexandra J.,Bere, Takudzwa,Dummer, Nicholas F.,Gong, Xiaoxiao,Hutchings, Graham J.,Lewis, Richard J.,Morgan, David J.,Richards, Nia,Shaw, Greg,Sun, Songmei
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p. 8052 - 8064
(2021/12/27)
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- Transfer hydrogenation of CO2into formaldehyde from aqueous glycerol heterogeneously catalyzed by Ru bound to LDH
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Aqueous glycerol was used in this study as a liquid-phase hydrogen source for the hydrogenation of CO2. It was found that hydrogen could be efficiently evolved from aqueous glycerol upon highly dispersed Ru on layered double hydroxide (LDH), inducing the transformation of CO2 into formaldehyde under base-free conditions at low temperature.
- Deng, Lidan,Liu, Xiaowei,Xu, Jie,Zhou, Zijian,Feng, Shixiang,Wang, Zheng,Xu, Minghou
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supporting information
p. 5167 - 5170
(2021/05/31)
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- Oxidation of dichloromethane over Au, Pt, and Pt-Au containing catalysts supported on γ-Al2O3 and CeO2-Al2O3
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Au, Pt, and Pt-Au catalysts supported on Al2O3 and CeO2-Al2O3 were studied in the oxidation of dichloromethane (DCM, CH2Cl2). High DCM oxidation activities and HCl selectivities were seen with all the catalysts. With the addition of Au, remarkably lower light-off temperatures were observed as they were reduced by 70 and 85 degrees with the Al2O3-supported and by 35 and 40 degrees with the CeO2-Al2O3-supported catalysts. Excellent HCl selectivities close to 100% were achieved with the Au/Al2O3 and Pt-Au/Al2O3 catalysts. The addition of ceria on alumina decreased the total acidity of these catalysts, resulting in lower performance. The 100-h stability test showed that the Pt-Au/Al2O3 catalyst was active and durable, but the selectivity towards the total oxidation products needs improvement. The results suggest that, with the Au-containing Al2O3-supported catalysts, DCM decomposition mainly occurs via direct DCM hydrolysis into formaldehyde and HCl followed by the oxidation of formaldehyde into CO and CO2
- Keiski, Riitta L.,Nevanper?, Tuomas K.,Ojala, Satu,Pitk?aho, Satu
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- Sonochemical Transformations of Methane and Ethylene in Aqueous Solutions under Conditions of Cavitation
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Abstract: The conversion of methane, ethylene and mixtures of them in aqueous solutions was studied using ultrasonic vibrations with a frequency of 22 kHz under conditions of cavitation. It is found that formaldehyde, the main product, forms even if there is no dissolved oxygen in the initial solution. It is shown that the rate of accumulation of formaldehyde depends on the power of the ultrasound and the amount of molecular oxygen introduced into the system.
- Arsentev, S. D.
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p. 1811 - 1815
(2020/09/09)
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- CATALYST WITH A CORE-SHELL STRUCTURE FOR METHANE OXIDATION, METHOD OF PREPARING THE SAME AND METHOD OF OXIDIZING METHANE USING THE SAME
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The present invention relates to a catalyst with a core-shell structure for methane oxidation, a method of preparing the same, and a method of methane oxidation using the same, and the catalyst comprises a core structure consisting of a nano-support and core nanoparticles; and a shell coating layer coated on the core structure in which the core nanoparticles have a particle diameter smaller than that of the nano-support and are coated on the nano-support to form a core structure, and it has excellent thermal stability during methane oxidation reaction at high temperature and an effect of increasing methane conversion and formaldehyde selectivity.
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Paragraph 19; 48; 49; 60-63
(2020/05/15)
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- Effect of Mo dispersion on the catalytic properties and stability of Mo-Fe catalysts for the partial oxidation of methanol
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Mo-Fe catalysts with different Mo dispersions were synthesized with fast (Cat-FS, 600 r·min?1) or slow stirring speed (Cat-SS, 30 r·min?1) by the coprecipitation method. Improving the stirring speed strengthened the mixing of the solution and increased the dispersion of particles in the catalyst, which exhibited favorable activity and selectivity. The byproduct (dimethyl ether (DME)) selectivity increased from 2.3% to 2.8% with Cat-SS, while it remained unchanged with Cat-FS in a stability test. The aggregation of particles and thin Mo-enriched surface layer decreased the catalyst surface area and slowed down the reoxidation of reduced active sites with Cat-SS, leaving more oxygen vacancies which promoted the formation of DME by the nonoxidative channel.
- Han, Minghan,Zhang, Shuai
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- Preparation and Application of Palladium Nanoparticle Impregnated Chloromethylated Polysulfone Matrix as an Efficient Catalytic Membrane for Oxidation of Alcohols
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The use of palladium nanoparticles embedded in a chloromethylated Polysulfone (CMPSf) matrix was developed for highly efficient oxidation of primary and secondary alcohols to corresponding aldehyde and ketone in organic solvent free condition. Pd (Π)/bis (2, 4-dihydroxybenzaldehyde) chelate chemically incorporated onto CMPSf was used to prepare beneficial catalytic membranes. Chemical structure and thermal properties of resulting membranes were characterized via FTIR, 1HNMR, UV-vis, TGA and DSC techniques. Morphology and particle distribution throughout the catalytic membranes was elucidated using FE-SEM. An average particle size of Pd nanoparticles was estimated about 20 nm by XRD technique. ICP technique proved that no Pd particles were leached out of the membrane into the solutions; hence the as-prepared catalytic membranes could be used several times without significant loss in their activities. This is in good accordance with formation of chemical bond between Pd and polymer matrix.
- Mahdavi, Hossein,Fayyazi, Faeze
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- Unraveling the cation and anion effects and kinetics for ionic liquid catalyzed direct synthesis of methyl acrylate under mild conditions
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The direct synthesis of methyl acrylate (MA) from methyl acetate and trioxane at 350-380 °C is regarded as a supplementary route for the industrial propylene oxidation process; however, it suffers from rapid catalyst deactivation. Herein, a novel ionic liquid catalyzed mild liquid-phase system was developed for the direct synthesis of MA from methyl acetate and trioxane, where N,O-bis(trimethylsilyl)acetamide (BSA) was used as a probase for α-deprotonation and enol silyl etherification of methyl acetate. The trioxane decomposition to formaldehyde and methyl acetate enolization to 1-methoxy-1-trimethylsilyloxyethene proceeded with the catalysis of [Cation]Cl/MClx (M = Cu+, Fe3+, Zn2+ and Al3+) and [Cation]F, respectively. The cations and anions were observed to have significant effects on the yield and selectivity of MA, owing to the steric hindrance, acid site category and strength confirmed by pyridine probing FT-IR characterization. As a result, up to 60.2% yield with 94.6% selectivity of MA could be achieved when [N3,3,3,3]F and [N3,3,3,3]Cl/AlCl3 with 67 mol% AlCl3 were used in the presence of BSA at 25 °C. Kinetic studies indicated that the trioxane decomposition with the activation barrier of 41.2 ± 0.3 kJ mol-1 was the rate-determining step.
- Wang, Gang,Li, Zengxi,Li, Chunshan,Zhang, Suojiang
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supporting information
p. 7913 - 7923
(2020/12/01)
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- μ-Nitrido-bridged iron phthalocyanine dimer bearing eight peripheral 12-crown-4 units and its methane oxidation activity
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A novel μ-nitrido-bridged iron phthalocyanine dimer with eight peripheral 12-crown-4 units as an electron-donating substituent was synthesized and characterized. Examination of its methane oxidation activity in the presence of H2O2 in an acidic aqueous solution suggested that the high-valent iron oxo species generated in situ was unstable and the transiently generated decomposed species showed methane oxidation activity via Fenton-type reaction. This journal is
- Yamada, Yasuyuki,Kura, Jyunichi,Toyoda, Yuka,Tanaka, Kentaro
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p. 19179 - 19183
(2020/11/23)
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- Catalytic H2O2 activation by a diiron complex for methanol oxidation
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In nature, C-H bond oxidation of CH4 involves a peroxo intermediate that decays to the high-valent active species of either a “closed” {FeIV(μ-O)2FeIV} core or an “open” {FeIV(O)(μO)FeIV(O)} core. To mimic and to obtain more mechanistic insight in this reaction mode, we have investigated the reactivity of the bioinspired diiron complex [(susan){Fe(OH)(μ-O)Fe(OH)}]2+ [susan = 4,7-dimethyl-1,1,10,10-tetrakis(2-pyridylmeth-yl)-1,4,7,10-tetraazadecane], which catalyzes CH3OH oxidation with H2O2 to HCHO and HCO2H. The kinetics is faster in the presence of a proton. 18O-labeling experiments show that the active species, generated by a decay of the initially formed peroxo intermediate [(susan){FeIII(μ-O)(μ-O2)FeIII}]2+, contains one reactive oxygen atom from the μ-oxo and another from the μ-peroxo bridge of its peroxo precursor. Considering an FeIVFeIV active species, a “closed” {FeIV(μ-O)2FeIV} core explains the observed labeling results, while a scrambling of the terminal and bridging oxo ligands is required to account for an “open” {FeIV(O)(μ-O)FeIV(O)} core.
- B?gge, Hartmut,Finke, Sebastian,Glaser, Thorsten,Ivanovic-Burmazovic, Ivana,Limpke, Thomas,Orth, Nicole,Stammler, Anja,Walleck, Stephan,Zimmermann, Thomas Philipp
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supporting information
p. 15563 - 15569
(2020/11/20)
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- Development of Na2Ti6O13/CuO/Cu2O heterostructures for solar photocatalytic production of low-carbon fuels
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Na2Ti6O13/CuO/Cu2O materials were prepared by solid-state and impregnation method, using copper oxide as cocatalyst (CC, 0.1%–5%). The catalytic activity was evaluated for H2 evolution and CO2 reduction. XPS analysis revealed the presence of Cu2O and CuO in different proportions. Na2Ti6O13 impregnated with 0.1% of cocatalyst exhibits majoritary the Cu2O phase; while Na2Ti6O13 with 5% of cocatalyst shows mainly CuO. Electrochemical measurements showed higher photocurrent and lower resistance to charge transference in Na2Ti6O13-0.1% CC, associated with better a charge flow. Na2Ti6O13-0.1% CC exhibited the highest H2 production (33 μmol g-1 h-1) and Na2Ti6O13-5% CC showed the best CO2 conversion to CH2O (25 μmol g-1 h-1) and CH3OH (4.6 μmol g-1 h-1). A major content of Cu2O phase favored the H2 evolution by the formation of a Z-scheme, where the strong negative character of the CB of Cu2O enhances the kinetics of H2O reduction, while a higher content of CuO improved CO2 adsorption and reduction.
- Ibarra-Rodríguez, Luz I.,Huerta-Flores, Ali M.,Torres-Martínez, Leticia M.
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- A nanoporous covalent organic framework for the green-reduction of CO2under visible light in water
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Herein, we designed a sheet-like nanoporous covalent organic framework (TFP-DM COF) based nanomaterial, which was formed via an easy solvothermal synthetic method. The as-synthesized material was characterized via FTIR spectroscopy, PXRD, UV-Vis, N2 adsorption-desorption studies, TEM and FESEM techniques. We demonstrated the photocatalytic reduction of CO2 into HCOOH and HCHO using the as-synthesized COF as the active photocatalyst and water as a green solvent as well as sacrificial electron source under atmospheric pressure. It was observed that the formaldehyde production rate was 36-fold higher than the formic acid production rate under white LED light irradiation. The catalyst showed good yields for both the products, HCOOH (0.019 mole) and HCHO (0.47 mole), even under sunlight irradiation. In addition, the COF material exhibited sufficient reusability without noticeable catalyst deactivation, which suggested the material to be a promising heterogeneous photocatalyst for commercial use in the CO2 reduction reaction under green reaction conditions.
- Das, Anjan,Hazra Chowdhury, Arpita,Hazra Chowdhury, Ipsita,Islam, Sk. Manirul,Khan, Aslam
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p. 11720 - 11726
(2020/07/21)
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- Utilizing hydrogen underpotential deposition in CO reduction for highly selective formaldehyde production under ambient conditions
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Formaldehyde is an essential building block for hundreds of chemicals and a promising liquid organic hydrogen carrier (LOHC), yet its indirect energy-intensive synthesis process prohibits it from playing a more significant role. Here we report a direct CO reduction to formaldehyde (CORTF) process that utilizes hydrogen underpotential deposition to overcome the thermodynamic barrier and the scaling relationship restriction. This is the first time that this reaction has been realized under ambient conditions. Using molybdenum phosphide as a catalyst, formaldehyde was produced with nearly a 100% faradaic efficiency in aqueous KOH solution, with its formation rate being one order of magnitude higher compared with the state-of-the-art thermal catalysis approach. Simultaneous tuning of the current density and reaction temperature led to a more selective and productive formaldehyde synthesis, indicating the electrochemical and thermal duality of this reaction. DFT calculations revealed that the desorption of the ?H2CO intermediate likely served as the rate-limiting step, and the participation of H2O made the reaction thermodynamically favorable. Furthermore, a full-cell reaction set-up was demonstrated with CO hydrogenation to HCHO achieved without any energy input, which fully realized the spontaneous potential of the reaction. Our study shows the feasibility of combining thermal and electrochemical approaches for realizing the thermodynamics and for scaling relationship-confined reactions, which could serve as a new strategy in future reaction design.
- Bentalib, Abdulaziz,Pan, Yanbo,Peng, Zhenmeng,Shen, Xiaochen,Wu, Dezhen,Yao, Libo
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p. 5639 - 5647
(2020/10/21)
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- Insights into Redox Dynamics of Vanadium Species Impregnated in Layered Siliceous Zeolitic Structures during Methanol Oxidation Reactions
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Supported transition metal catalysts have been extensively applied to oxidative and reductive processes. The understanding of surface speciation and active site-support interactions in these materials play a substantial role in developing improved heterogeneous catalysts. Herein, a series of impregnated 3D ferrierite and 2D ITQ-6 siliceous supports with variable loading of vanadium oxide was prepared. Chemical and structural properties of the materials were studied by X-ray diffraction, N2 physisorption, inductively coupled plasma – optical emission spectrometry, X-ray absorption, Fourier transform infrared and diffuse reflectance UV-vis spectroscopies, and temperature-programmed reduction with H2. Reactivity of the catalyst surface, associated with the incidence of isolated silanol groups, was found to be more effective when vanadium oxides were better dispersed and stabilized than increases in surface area. Differences in activation and the oxidation state dynamic behavior of active sites were then probed by methanol oxidation as a model reaction monitored by in situ FTIR spectroscopy and XANES/MS. By applying isothermal periods of reaction under non-oxidizing atmosphere and regeneration of catalysts by O2, it was found that, even at distinct rates, all types of sites are accessible during reaction, since a complete reduction to V4+ was observed. However, reoxidation of sites to V5+ is limited and sensitive to the different vanadium species on the surface, and probably, the determinant factor of the distinct V5+/V4+ equilibrium reached for the catalysts when the reaction is carried out under constant oxidizing atmosphere.
- Vieira, Luiz H.,Possato, Luiz G.,Chaves, Thiago F.,Lee, Jason J.,Sulmonetti, Taylor P.,Jones, Christopher W.,Martins, Leandro
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p. 141 - 151
(2019/11/13)
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- Singlet oxygen generation by the reaction of acrolein with peroxynitrite via a 2-hydroxyvinyl radical intermediate
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Acrolein (2-propenal) is an environmental pollutant, food contaminant, and endogenous toxic by-product formed in the thermal decomposition and peroxidation of lipids, proteins, and carbohydrates. Like other α,β-unsaturated aldehydes, acrolein undergoes Michael addition of nucleophiles such as basic amino acids residues of proteins and nucleobases, triggering aging associated disorders. Here, we show that acrolein is also a potential target of the potent biological oxidant, nitrosating and nitrating agent peroxynitrite. In vitro studies revealed the occurrence of 1,4-addition of peroxynitrite (k2 = 6 × 103 M?1 s?1, pH 7.2, 25 °C) to acrolein in air-equilibrated phosphate buffer. This is attested by acrolein concentration-dependent oxygen uptake, peroxynitrite consumption, and generation of formaldehyde and glyoxal as final products. These products are predicted to be originated from the Russell termination of ?OOCH=CH(OH) radical which also includes molecular oxygen at the singlet delta state (O2 1Δg). Accordingly, EPR spin trapping studies with the 2,6-nitrosobenzene-4-sulfonate ion (DBNBS) revealed a 6-line spectrum attributable to the 2-hydroxyvinyl radical adduct. Singlet oxygen was identified by its characteristic monomolecular IR emission at 1,270 nm in deuterated buffer, which was expectedly quenched upon addition of water and sodium azide. These data represent the first report on singlet oxygen creation from a vinylperoxyl radical, previously reported for alkyl- and formylperoxyl radicals, and may contribute to better understand the adverse acrolein behavior in vivo.
- Augusto, Ohara,Bechara, Etelvino J. H.,Di Mascio, Paolo,Gon?alves, Leticia C. P.,Klassen, Aline,Licciardi, Saymon,Linares, Edlaine,Massari, Júlio,Prado, Fernanda M.,Tavares, Marina F. M.
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- Pd-Pt bimetallic Nb-doped TiO2 for H2 photo-production: Gas and liquid phase processes
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The performance of binary PtPd co-catalysts supported on Nb-TiO2 was tested in the gas and liquid phase photo-reforming of methanol. Co-catalyst formulations having Pt:Pd ratios from 2:1 to 1:4 were tested and the activity measured through the calculation of the quantum efficiency. Characterization of the initial and post-reaction materials showed that optimum activity is achieved in both processes by samples containing binary co-catalysts where Pd suffers an oxidation process and a PtPd alloying metallic phase is formed under reaction conditions. The analysis of catalytic output through an experimental design considering tree factors (methanol:water ratio, irradiance level, and catalyst volumetric concentration at liquid phase or surface concentration at gas phase) shows that the liquid phase process presents a rather high quantum efficiency value compared with the gas phase but the latter process displays higher atom efficiency as well as renders products with lower toxicity.
- Caudillo-Flores, Uriel,Mu?oz-Batista, Mario J.,Kubacka, Anna,Fernández-García, Marcos
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- METHODS FOR PREPARING FORMALDEHYDE FROM CARBON DIOXIDE
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The present disclosure provides, inter alia, methods for preparing formaldehyde from carbon dioxide using bis(silyl)acetals, methods for incorporating carbon derived from carbon dioxide into a complex organic molecule derived from formaldehyde using bis(silyl)acetals, and methods for generating an isotopologue of a complex organic molecule derived from formaldehyde using bis(silyl)acetals.
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Paragraph 0040; 0042; 0043
(2020/11/27)
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- Manganese(I)-Catalyzed β-Methylation of Alcohols Using Methanol as C1 Source
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Highly selective β-methylation of alcohols was achieved using an earth-abundant first row transition metal in the air stable molecular manganese complex [Mn(CO)2Br[HN(C2H4PiPr2)2]] 1 ([HN(C2H4PiPr2)2]=MACHO-iPr). The reaction requires only low loadings of 1 (0.5 mol %), methanolate as base and MeOH as methylation reagent as well as solvent. Various alcohols were β-methylated with very good selectivity (>99 %) and excellent yield (up to 94 %). Biomass derived aliphatic alcohols and diols were also selectively methylated on the β-position, opening a pathway to “biohybrid” molecules constructed entirely from non-fossil carbon. Mechanistic studies indicate that the reaction proceeds through a borrowing hydrogen pathway involving metal–ligand cooperation at the Mn-pincer complex. This transformation provides a convenient, economical, and environmentally benign pathway for the selective C?C bond formation with potential applications for the preparation of advanced biofuels, fine chemicals, and biologically active molecules.
- Kaithal, Akash,van Bonn, Pit,H?lscher, Markus,Leitner, Walter
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supporting information
p. 215 - 220
(2019/12/03)
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- Selective Deposition of Cobalt and Copper Oxides on BiVO4 Facets for Enhancement of CO2 Photocatalytic Reduction to Hydrocarbons
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The nanostructure of a semiconductor is a crucial parameter for efficient photocatalytic performance. Hereby, we have synthesized monoclinic bismuth vanadate (BiVO4) crystals with controlled ratio of {010} and {110} facets. The selective deposition of CuOx and CoOx over {010} and {110} facets has been performed using photo-reduction and photo-oxidation methods, respectively. It resulted in a highly efficient charge separation of photogenerated electrons and holes and enhancement of the photocatalytic reduction of CO2 by H2O into hydrocarbons, including CH4, C2H6 and C3H8. The controlled co-catalyst deposition over different semiconductor facets provides a strategy for the synthesis of hydrocarbons from CO2 and H2O by efficient charge separation.
- Yu, Xiang,Ordomsky, Vitaly V.,Khodakov, Andrei Y.
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p. 740 - 749
(2020/01/21)
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- Substrate-Assisted Hydroxylation and O-Demethylation in the Peroxidase-like Cytochrome P450 Enzyme CYP121
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CYP121 is a P450 enzyme from Mycobacterium tuberculosis that catalyzes a C-C coupling reaction between the two aromatic rings on its native substrate cyclo(l-Tyr-l-Tyr) (cYY) to form mycocyclosin, a necessary product for cell survival. Unlike the typical P450 enzymes for hydroxylation, CYP121 is believed to behave like a peroxidase and conduct radical-mediated C-C bond formation. Here, we probe whether the phenolic hydrogen of the substrate is the site of the postulated hydrogen atom abstraction for radical formation. We synthesized a singly O-methylated substrate analogue, cYF-4-OMe, and characterized its interaction with CYP121 by ultraviolet-visible and electron paramagnetic resonance spectroscopies and X-ray crystallography. We found that cYF-4-OMe can function as a substrate of CYP121 using the established assay via the peroxide shunt. Analysis of the enzymatic reaction revealed an O-demethylation of cYF-4-OMe instead of cyclization, yielding cYY and formaldehyde. A hydroxylated substrate, cYF-4-OMeOH, is expected to be the intermediate product, which was trapped and structurally characterized by X-ray crystallography. We further determined that the deformylation reaction of cYF-4-OMeOH proceeds via an alkyl-oxygen rather than aryl-oxygen bond cleavage by the 18O-labeling studies. Finally, the pH dependence catalytic study on the native substrate and the methoxy analogue further supports the mechanistic understanding that the hydrogen atom abstraction is the critical first oxidation step exerted by a heme-based oxidant during the cyclization reaction of cYY. The switch in catalytic activity reveals the power of CYP121 as a P450 enzyme and provides insight into the peroxidase-like catalytic mechanism.
- Nguyen, Romie C.,Yang, Yu,Wang, Yifan,Davis, Ian,Liu, Aimin
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p. 1628 - 1639
(2020/02/04)
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- Visible light-assisted reduction of CO2 into formaldehyde by heteroleptic ruthenium metal complex-TiO2 hybrids in an aqueous medium
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The photocatalytic reduction of CO2 with its simultaneous functionalization is a profound journey to achieve under an ambient condition. In the current research, precedence exists for the formation of HCHO, HCOOH, CO, CH4, and CH3OH after the reduction of CO2 under suitable conditions. In this progression, HCHO is considered to be a reactive molecule, which occurs in the photocatalysis under suitable condition observed in the photocatalytic process. Herein, we report CO2 reduction to formaldehyde via heterogeneous photocatalysis in an aqueous medium at pH 7. The as-synthesized hybrid photocatalyst is capable of being active under visible light (λ > 420 nm) by utilizing the heteroleptic ruthenium metal complex over TiO2 nanoparticles via covalent interactions. The major reaction product was identified as formaldehyde, while trace amounts of CO and CH4 were also detected in the presence of triethanolamine (TEOA) as a sacrificial donor. The maximum turnover number (720) for HCHO was obtained based on the metal complex used over the surface after 5 h visible light irradiation. Furthermore, formaldehyde (in situ) was utilized for the reaction with primary amines (aniline, 4-aminobenzoic acid) to form the corresponding imines under visible light. Directed by mechanistic studies, the results indicate for the first time that the C1 reduced product of CO2 in a heterogeneous medium can be utilized for synthesis of useful products.
- Kumar, Alok,Ananthakrishnan, Rajakumar
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supporting information
p. 1650 - 1661
(2020/03/23)
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- Photooxidation Reactions of Ethyl 2-Methylpropionate (E2MP) and Ethyl 2,2-Dimethylpropionate (E22DMP) Initiated by OH Radicals: An Experimental and Computational Study
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The relative rate (RR) technique was used for the measurement of OH-initiated photooxidation reactions of ethyl 2-methylpropionate (E2MP) and ethyl 2,2-dimethylpropionate (E22DMP) in the temperature range of 268-363 K at 760 Torr. In addition to this, the
- Kaipara, Revathy,Rajakumar, B.
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p. 2768 - 2784
(2020/05/08)
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- Reductive Electrochemical Activation of Molecular Oxygen Catalyzed by an Iron-Tungstate Oxide Capsule: Reactivity Studies Consistent with Compound i Type Oxidants
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The reductive activation of molecular oxygen catalyzed by iron-based enzymes toward its use as an oxygen donor is paradigmatic for oxygen transfer reactions in nature. Mechanistic studies on these enzymes and related biomimetic coordination compounds designed to form reactive intermediates, almost invariably using various "shunt" pathways, have shown that high-valent Fe(V)=O and the formally isoelectronic Fe(IV) =O porphyrin cation radical intermediates are often thought to be the active species in alkane and arene hydroxylation and alkene epoxidation reactions. Although this four decade long research effort has yielded a massive amount of spectroscopic data, reactivity studies, and a detailed, but still incomplete, mechanistic understanding, the actual reductive activation of molecular oxygen coupled with efficient catalytic transformations has rarely been experimentally studied. Recently, we found that a completely inorganic iron-tungsten oxide capsule with a keplerate structure, noted as {Fe30W72}, is an effective electrocatalyst for the cathodic activation of molecular oxygen in water leading to the oxidation of light alkanes and alkenes. The present report deals with extensive reactivity studies of these {Fe30W72} electrocatalytic reactions showing (1) arene hydroxylation including kinetic isotope effects and migration of the ipso substituent to the adjacent carbon atom ("NIH shift"); (2) a high kinetic isotope effect for alkyl C - H bond activation; (3) dealkylation of alkylamines and alkylsulfides; (4) desaturation reactions; (5) retention of stereochemistry in cis-alkene epoxidation; and (6) unusual regioselectivity in the oxidation of cyclic and acyclic ketones, alcohols, and carboxylic acids where reactivity is not correlated to the bond disassociation energy; the regioselectivity obtained is attributable to polar effects and/or entropic contributions. Collectively these results also support the conclusion that the active intermediate species formed in the catalytic cycle is consistent with a compound I type oxidant. The activity of {Fe30W72} in cathodic aerobic oxidation reactions shows it to be an inorganic functional analogue of iron-based monooxygenases.
- Bugnola, Marco,Shen, Kaiji,Haviv, Eynat,Neumann, Ronny
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p. 4227 - 4237
(2020/05/05)
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- The influence of H/D kinetic isotope effect on radiation-induced transformations of hydroxyl-containing compounds in aqueous solutions
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Vicinal diols and its derivatives can be exploited as model compounds for the investigation of radiation-induced free-radical transformations of hydroxyl-containing biomolecules such as carbohydrates, phospholipids, ribonucleotides, amino acids, and peptides. In this paper, for the first time, the prospects of isotope reinforcement approach in inhibiting free-radical transformations of hydroxyl-containing compounds in aqueous solutions are investigated on the example of radiolysis of 1,2-propanediol and 1,2-propanediol-2-d1 aqueous solutions. At an absorbed dose rate of 0.110 ± 0.003 Gy·s?1 a profound kinetic isotope effect (KIE) is observed for the non-branched chain formation of acetone, which is a final dehydration product of predominant carbon-centred radicals CH3·C(OH)CH2OH. In 0.1 and 1 M deaerated solutions at pH 7.00 ± 0.01, the values of KIE are 8.9 ± 1.7 and 15.3 ± 3.1, respectively. A rationale for the fact that a strong KIE takes place only in the case of chain processes, which may occur during free-radical transformations of vicinal diols, is also provided herein based on the results of 2-propanol and 2-propanol-2-d1 indirect radiolysis. Lastly, the lack of KIE is shown in the case of 2-butanone formation from 2,3-butanediol or 2,3-butanediol-2,3-d2. This indicates that the type (primary, secondary) of the β-carbonyl radicals formed as a result of CH3·C(OH)CH(OH)R (R = H, CH3) dehydration determines the manifestation of the effect.
- Bekish, Andrei V.,Nepachalovich, Palina S.,Shadyro, Oleg I.,Shmanai, Vadim V.
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p. 732 - 744
(2020/12/28)
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- Bimetallic gold-silver catalysts based on ZnO and Zn/SBA-15 – The effect of various treatments on surface and catalytic properties
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Two different supports containing zinc (ZnO and Zn/SBA-15) were used to prepare mono- and bimetallic gold, silver and gold-silver catalysts. Zinc was used for two different purposes in these materials: (i) as a support in the form of zinc oxide and (ii) as a dopant introduced to short-channel SBA-15 by wetness impregnation. Short channel SBA-15 was used as the reference support. The materials obtained were characterized by: N2 physisorption, XRD, TEM, UV–vis, XPS, XAS and their activity was tested in the reactions of propene and methanol oxidation in the gas phase. The state of metals (Au, Ag, Zn) and the composition of gold-silver alloy formed on the catalysts surface were considered in terms of thermal activation of catalysts in inert gas and in hydrogen flow as well as interaction with reagents and products of methanol and propene oxidation. It was found that silver species were responsible for the activity in propene oxidation and its total combustion to CO2, whereas (Au0)δ? metallic particles were active in methanol oxidation. Selectivity to acrolein in propene oxidation was achieved thanks to the presence of Au-Ag alloy whose composition depended on the presence of zinc oxide and activation conditions. The alloy was not stable and separated into metals upon propene oxidation conditions. In methanol oxidation, zinc species took part in selective oxidation to methyl formate.
- Kaskow, Iveta,Sobczak, Izabela,Yang, Chia-Min,Ziolek, Maria
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p. 110 - 121
(2019/06/24)
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- Epoxidation of Ethylene with Products of Thermal Gas-Phase Oxidation of n-Butane
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Abstract: Epoxidation of ethylene with the reactive products formed during thermal gas-phase oxidation of n-butane has been carried out under flow conditions with the separation of the zones of generation of radicals and their interaction with ethylene. Butane is oxidized in the first section of a two-section reactor, and ethylene is fed to the second section. It has been found that increasing the residence time of a butane–oxygen mixture in the first section of the reactor from 7 to 13 s increases the ethylene oxide accumulation rate. A further increase in the contact time leads to a decrease in the rate. Similarly, increasing the C4H10/O2 ratio in the range of 0.05–0.25 leads to an increase in the rate of accumulation of ethylene oxide. A further increase in this ratio decreases the rate of epoxidation. It has also been found that the temperature dependences of the ethylene oxide accumulation rate in both sections of the reactor pass through a maximum. The obtained data give evidence for the occurrence of the ethylene epoxidation reaction initiated by the n-butane oxidation products under the conditions when ethylene itself is slightly oxidized.
- Arsentev, S. D.,Grigoryan, R. R.
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p. 187 - 193
(2020/03/30)
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- Synthesis of High Dimensionally Structured Mo-Fe Mixed Metal Oxide and Its Catalytic Activity for Selective Oxidation of Methanol
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High-dimensionally structured Mo-Fe oxide (HDS-MoFeO) was synthesized through an assembly of structural units supplied from Keplerate-type polyoxometalate, {Mo72Fe30}, under an appropriate hydrothermal condition. HDS-MoFeO showed excellent catalytic activity for the selective oxidation of methanol with slightly lower selectivity for formaldehyde than that of a conventional Mo-Fe oxide catalyst.
- Hiyoshi, Norihito,Ishikawa, Satoshi,Kumaki, Masahiro,Shimoda, Kosuke,Tashiro, Masaya,Ueda, Wataru
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supporting information
(2020/04/15)
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