- Catalytic hydrosilylation of oxalic acid: Chemoselective formation of functionalized C2-products
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Oxalic acid is an attractive entry to functionalized C2-products because it can be formed by C-C coupling of two CO2 molecules under electrocatalytic reduction. Herein, we describe the first attempts to reduce oxalic acid by catalytic hydrosilylation. Using B(C6F 5)3 as a Lewis acidic catalyst, oxalic acid can be converted to reduced C2-molecules, with high chemoselectivity, under mild reaction conditions.
- Feghali, Elias,Jacquet, Olivier,Thuery, Pierre,Cantat, Thibault
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- Oxidative Condensation of Methane on Sr2 –xLaxTiO4 Catalysts: Effect of the Degree of Substitution of Sr and La
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Abstract: The Sr2 –xLaxTiO4 (x = 0–2.0) catalysts were synthesized based on strontium titanate with a layered perovskite structure. The effect of the degree of substitution of La for Sr on the physicochemical (phase composition and textural characteristics) and catalytic properties of oxides in the oxidative condensation of methane at temperatures of 700–800°C were studied. It was found that multiphase Sr2?–?xLaxTiO4 samples with the degree of substitution x = 0.8–1.8 were most active and selective in the test reaction; this was likely related to the presence of lanthanum oxide and strontium oxide impurities in them, their optimum distribution over the surface, and the specific surface area.
- Petrov,Ivanova, Yu. A.,Reshetnikov,Isupova
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- New mechanism of photodissociation of gaseous acetone
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It is found for the first time that photolysis of gaseous acetone under UV irradiation produces ethane not only via recombination of methyl radicals, but also by the mechanism of induced predissociation.
- Skorobogatov,Meilakhs,Pogosyan,Khripun
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- Mechanisms of 1,1-Reductive Elimination from Palladium: Elimination of Ethane from Dimethylpalladium(II) and Trimethylpalladium(IV)
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The energies and entropies of activation for the 1,1-reductive elimination of ethane from cis-bis(diphenylmethylphosphine)dimethylpalladium(II) (2a) in polar and nonpolar solvents were determined.The rates of elimination are slower in polar solvents such as Me2SO, acetone, and acetonitrile than in nonpolar solvents such as benzene.The energies of activation in nonpolar solvents are very close (25 kcal/mol) to the calculated values (extended HMO).Lower energies of activation (6-10 kcal/mol) but high negative entropies of activation (ca.45 eu) in polar solvents are consistent with an elimination that produced a coordinatively unsaturated palladium(0) complex and a late transition state having the characteristics of the product, such that solvent coordinates during the transition state.Reaction of 2a or the corresponding bis(triphenylphosphine)dimetnylpalladium(II) complex 2b with methyl iodide yields ethane and the trans-bis(phosphine)iodomethylpalladium(II) complexes (10a,b).The second-order reaction proceeds through a rate-determining oxidative addition of methyl iodide to 2a,b, yielding the bis(phosphine)iodotrimethylpalladium(IV) intermediate, followed by a rapid elimination.In polar solvents, the rates of these reactions are faster than the 1,1-reductive eliminations from 2a,b mostly because of the lower entropies of activation in the oxidative addition step.In nonpolar solvents, the rates are comparable.The reaction of 2a,b with CD3I gave both C2H6 and C2H3D3, the ratios of these isomers in the reaction of 2a being most consistent with the trans oxidative addition reaction followed by statistical reductive elimination from adjacent methyls.
- Moravskiy, A.,Stille, J. K.
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- Gold-doping of carbon-supported palladium improves reduction catalysis
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Bimetallic palladium-gold (PdAu) catalysts have better catalytic performance than monometallic catalysts for many applications. PdAu catalysts with controlled nanostructures and enhanced activities have been extensively studied but their syntheses require multiple and occasionally complicated steps. In this work, we demonstrated that supported PdAu catalysts could be simply prepared by doping a supported Pd catalyst with gold through wet impregnation and calcination. Resulting PdAu-on-carbon (PdAu/C) catalysts were tested for the room-temperature, aqueous-phase hydrodechlorination of trichloroethene. The most active PdAu/C catalyst (Pd 1.0 wt%, Au 1.1 wt%, dried/air/H2 process) had an initial turnover frequency (TOF) of 34.0 × 10?2 molTCE molPd?1 s?1, which was >15 times higher than monometallic Pd/C (Pd 1.0 wt%, initial TOF of 2.2 × 10?2 molTCE molPd?1 s?1). Through X-ray absorption spectroscopy, the gold kept Pd from oxidizing under calcination at 400 °C. Probable nanostructure evolution pathways are proposed to explain the observed catalysis.
- Fang, Yu-Lun,Heck, Kimberly N.,Zhao, Zhun,Pretzer, Lori A.,Guo, Neng,Wu, Tianpin,Miller, Jeffrey T.,Wong, Michael S.
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- Arrhenius Parameter Determination for the Reaction of Methyl Radicals with Iodine Species in Aqueous Solution
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The techniques of electron pulse radiolysis and direct ESR detection have been used to determine Arrhenius parameters for the recombination reaction of methyl radicals and methyl radical reaction with iodine in aqueous solution.At 22.8 deg C, rate constants of 2k7=(1.77+/-0.16)E9 dm3 mol-1 s-1 and k1=(2.75+/-0.43)E9 dm3 mol-1 s-1, with corresponding activation energies of 14.89+/-0.87 and 13.10+/-0.71 kJ mol-1 (5.7-39.6 deg C), were obtained respectively for these two reactions.The analogous reaction of methyl radicals with iodide or iodate was found to be much slower, with the room temperature rate constant for both reactions estimated as k3 mol-1 s-1.
- Mezyk, Stephen P.,Madden, Keith P.
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- Kinetic limit of the ethane and ethylene yield in the gas phase condensation of methane
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A kinetic simulation of the initiated condensation of methane in the gas phase showed that the additional generation of methyl radicals via the reaction CH4 + I2 -> CH3 + HO2 causes a nearly tenfold increase in the C2 hydrocarbon yield.However, a kinetic limit of the yield exist that is close to that determined in experiments on the catalytic oxidative condensation of methane. - Key words: kinetic simulation; oxidative condensation of methane.
- Vedeneev, V. I.,Arutyunov, V. S.,Basevich, V. Ya.
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- Variability of particle configurations achievable by 2-nozzle flame syntheses of the Au-Pd-TiO2 system and their catalytic behaviors in the selective hydrogenation of acetylene
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Catalysts with Au and Pd supported on TiO2 (Au:Pd 1:1 wt/wt%) were prepared by 1- and 2-nozzle flame spray pyrolysis (FSP). The 2-nozzle configuration allowed to synthesize various particle configurations by separate or co-feeding of the metal precursor solutions to the two nozzles. For the Au-Pd/TiO2 system, four different catalyst particle configurations were investigated: “TiO2 + AuPd”, “Pd/TiO2 +Au”, “Au/TiO2 +Pd”, and “Pd/TiO2 + Au/TiO2”, where + separates the corresponding precursor solutions fed to the two nozzles. There were no significant differences in the specific surface areas and the average TiO2 crystallite sizes of the catalysts (100 m2/g and 16–17 nm, respectively) with the exception of “Pd/TiO2 +Au/TiO2”, which exhibited larger surface area and smaller crystallite size (152 m2/g, 12 nm) due to halving of the Ti precursor concentration in each nozzle. As revealed by CO chemisorption, XPS, and STEM-EDX results, the catalyst properties varied largely in terms of bimetallic AuPd particle compositions, the interaction between metal–metal and metal-support, and the location of Pd (or AuPd) on the TiO2. Among the catalysts studied, “TiO2 + AuPd” prepared with the 2-nozzle system exhibited the highest conversion of acetylene (~50%) at 40 °C with high selectivity to ethylene ( > 95%). Co-feeding the noble metal precursors together with the Ti precursor afforded less active catalysts due to the formation of Ti-O species partially covering the most active bimetallic AuPd particles. Compared to the commercially available acetylene hydrogenation catalyst and the AuPd/TiO2 prepared by conventional co-impregnation and deposition-precipitation, all the FSP-AuPd/TiO2 catalysts showed superior performances under the reaction conditions used.
- Pongthawornsakun, Boontida,Mekasuwandumrong, Okorn,Santos Aires, Francisco J.Cadete,Büchel, Robert,Baiker, Alfons,Pratsinis, Sotiris E.,Panpranot, Joongjai
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- Oxidative Coupling of Methane over Na2WO4/CeO2 and Related Catalysts
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Na2WO4/CeO2 is an active and selective catalyst for the oxidative coupling of methane (OCM).At 780 deg C and using a reactant feed of CH4:O2:He=4.8:1.0:5.6, a C2 selectivity in excess of 70percent can be achieved over a 9.4 molpercent Na2WO4/CeO2 catalyst at a CH4 conversion of 22percent.By contrast, the C2 selectivity exhibited by pure CeO2 under the same reaction conditions, in the absence of Na2WO4 promoter, is 2- on the calcined catalysts and reveal no evidence for additional surface oxygen species, such as O22- or O-, that might serve as sites for CH4 activation.Pulse reaction experiments show that bulk lattice oxygen species do not participate directly in the OCM reaction, and that the active oxygen species involved in the activation of methane exist only in the presence of gas phase oxygen.Ion scattering spectroscopy and in situ Raman spectroscopy indicate that the initial CeO2 surface of the calcined catalyst is completely covered by one or more layers of Na2WO4, which exists in the molten state under reaction conditions.
- Yu, Zhenqiang,Yang, Xueming,Lunsford, Jack H.,Rosynek, Michael P.
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- Novel catalysts for carbon dioxide-induced selective conversion of methane to C2 hydrocarbons
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The combination of Mn with BaCO3 leads to active catalysts for carbon dioxide-induced selective conversion of methane to ethane and ethylene in the absence of oxygen.
- Cai, Yingchun,Chou, Lingjun,Li, Shuben,Zhang, Bing,Zhao, Jun
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- Gas-Phase Proton Affinities for H2O, C2H4 and C2H6
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Rate and equilibrium constant measurements are reported which provide proton affinities for H2O, C2H4, and C2H6 and heats of formation for the corresponding protonated species at 298 K, on the basis of the well-established proton affinity of CO.The values recommended for the proton affinities are 165.3 +/- 1.8, 163.0 +/- 1.7, and 142.1 +/-1.2 kcal mol-1 for H2O, C2H4, and C2H6, respectively.The proton affinity obtained for H2O is lower than accepted values.The results obtained for C2H4 agree almost exactly with those obtained in a very recent photoionization (PIPECO) study by Baer.The measurements with C2H6 provide a new accurate determination of its proton affinity.
- Bohme, Diethard K.,Mackay, Gervase I.
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- The Role of Coke in Acetylene Hydrogenation on Pd/α-Al2O3
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The formation of coke and the influence of the coke on selectivity were investigated during hydrogenation of acetylene on supported palladium catalysts. It was found that the total amount of coke was not directly related to the increase in formation of undesired ethane. Instead, the surface coverage of hydrogen during the deactivation was found to be a crucial parameter. A catalyst deactivated at low hydrogen surface coverage showed a higher ethane selectivity than a sample deactivated at higher surface coverage of hydrogen when compared under the same reaction conditions. In contrast, the coke formation rate was found to increase with increased hydrogen surface coverage. The role of carbon monoxide was also investigated, and the impact on selectivity and coke formation was explained by the reduced surface coverage of hydrogen in the presence of carbon monoxide. The coke was characterized by temperature-programmed oxidation, and deconvolution of the obtained peaks was carried out using a power-law model.
- Larsson, Mikael,Jansson, Jonas,Asplund, Staffan
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- Mechanistic Aspects of Oxidative Coupling of Methane over LaAlO3
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Mechanistic aspects of the oxidative coupling reaction of methane over an LaAlO3 catalyst (La:Al=1:1) prepared by the mist decomposotion method have been studied, using both contonuous-flow and pulsed-flow techniques.The delayed pulse technique together with temperature-programmed desorption reveal that an adsorbed oxygen species is effective in the formation of the C2 compounds, while a gaseous or weakly adsorbed oxygen species is involved in the combustion reaction.Methane cannot stay on the surface stably.Comparing these results with those obtained using the continuous flow reactor, mechanistic aspects are considered from the viewpoint of oxygen activity.The stability of this catalyst is also discussed.
- Tagawa, Tomohiko,Imai, Hisao
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- Tailoring the physical and catalytic properties of lanthanum oxycarbonate nanoparticles
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The synthesis of lanthanum oxide and its carbonate analogues has been performed by flame spray pyrolysis (FSP). Two different feeds have been studied: an organic solution and an aqueous/organic microemulsion. A key experimental parameter of FSP, the O2 dispersion, i.e., the flow rate of the dispersing gas in the FSP nozzle, exhibits an effect on the properties of the materials prepared. Increasing the level of O2 dispersion led to an increase in surface area and a decrease in mean particle size and basicity when a lanthanum containing organic solution was used as FSP feed. Lanthanum can form different phases, such as oxides, hydroxides, oxycarbonates and carbonates. The increase of O2 dispersion also produced a phase change, going from a mixture of type Ia and type II La2O2CO3 and La2O3 to pure La2O3. The use of an aqueous/organic microemulsion feed, which had a higher viscosity than the organic feed, resulted in materials with a lower surface area and a higher mean particle size than those prepared using the organic solution at the same O2 dispersion. In this case a mixture of type II La2O2CO3 and La2O3 was obtained. The materials were tested for oxidative coupling of methane (OCM). We were able to demonstrate that the OCM performance of the materials could be modified by changing the synthesis parameters. For example, lower O2 dispersion produced the highest CH4 and O2 conversions. We also demonstrated that on ageing the mean particle size remain stable; however, the phases do not, showing a new phase, La(OH)3, formation and resulting in an increase in OCM activity. While the OCM performances are modest they do demonstrate the power of this approach for controlled synthesis of lanthanum materials.
- Estruch Bosch,Copley,Eralp,Bilbé,Thybaut,Marin,Collier
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- The effect of pressure on the surface structure of MgO/BaCO3 catalyst for oxidative coupling of methane
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The effect of pressure on oxidative coupling of methane (OCM) over MgO/BaCO3 catalyst was studied at the range of 0.1~1.1MPa at 1053 K. Deactivation of the MgO/BaCO3 catalyst at elevated pressure was attributed to the migration of BaCO3 from bulk to the surface of the catalyst.
- Liu, Yu,Yu, Changchun,Liu, Xuxia,Zhang, Bing,Shen, Shikong
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- Oxidative Coupling of Methane over SrCO3 and SrO
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The oxidative coupling of methane has been studied with an SrCO3-SrO mixed catalyst.Two surface states (an SrO-rich surface and an SrCO3-rich surface) were prepared and examined by various methods including XPS.SrO-rich surfaces, prepared by H2 treatment of SrCO3, had a high C2 yield, and evolved CO2 was absorbed by the catalyst at 1023 K.The bulk diffusion of CO2 was considered to be rapid enough to absorb most of the evolved CO2 and to keep SrO partly on the surface (SrCO3-rich surface) at 1023 K.SrCO3-rich surfaces gave low C2 yields, and the surface was composed of both oxides and carbonates.The active sites were considered to be oxides.The SrO surface was more active than MgO in this reaction.However, it was less active under the steady state because of carbonate formation.
- Aika, Ken-ichi,Aono, Kenji
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- Oxidative coupling of methane in the redox cyclic mode over the Ag-La2O3/SiO2 catalytic system
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Synergism of Ag and La2O3 in the Ag-La2O3/SiO2 catalytic system provides substantial efficiency in oxidative coupling of methane carried out in the redox cyclic mode. Selectivity to C2 products can be raised by preliminary injection of small amount of hydrogen to the catalyst.
- Greish, Alexander A.,Glukhov, Lev M.,Finashina, Elena D.,Kustov, Leonid M.,Sung, Jae-Suk,Choo, Ko-Yeon,Kim, Tae-Hwan
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- Electrocatalytic Dehalogenation of 1,2-DihaIoethanes by the C60, C70, C76, C78, and C84 Fullerene Anions: Structure-Reactivity Aspects
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The homogeneous electrocatalytic reduction of 1,2-dihaloethanes by anions of larger fullerenes, C76, C78, and C84, is presented, and structure-reactivity correlations are derived by including our data reported earlier for the C60 and C70 electrocatalytic process. Cyclic voltammetry measurements indicate that dianions of C76 and C78, as well as trianions of C76, C78, and C84, electrochemically generated in 0.1 M (TBA)PF6, in benzonitrile, catalyze dehalogenation of 1,2-dihaloethanes. Values of the second-order rate constant, k, for the electrocatalytic dehalogenation of 1,2-dihaloethanes by the fullerene anions were determined by using the rotating-disk electrode voltammetry under pseudo-first-order conditions with respect to the 1,2-dihaloethanes. For each fullerene anion, k increases in the order: Cl 84 78 76 70 60, as a function of respective redox potentials of the fullerene, for each 1,2-dihaloethane. Unlike the C60n- electrocatalysis, reported by us earlier to be accompanied by chemical reaction between C60n- and certain ?±,??-diiodoalkanes yielding alkyl adducts of C60, no reaction between the anions of larger fullerenes and 1,2-dihaloethanes was observed within the voltammetric time scale. Because of the high stability with respect to adduct formation and more positive potentials of the electrocatalyses, the larger fullerenes may be more useful than C60 as catalysts, even though the corresponding catalytic rate constants are smaller.
- D'Souza, Francis,Choi, Jai-Pil,Kutner, Wlodzimierz
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- Fine structural photoluminescence spectra of silica-supported zirconium oxide and its photoactivity in direct methane conversion
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Highly dispersed zirconium oxide species on silica exhibit fine structure in phosphorescence emission spectra showing the vibration energy of the photoactive Zr-O-Si linkage to be 955 cm-1, and the species promotes the photoinduced non-oxidativ
- Yoshida, Hisao,Chaskar, Manohar G.,Kato, Yuko,Hattori, Tadashi
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- A structurally rigid bis(amido) ligand framework in low-coordinate Ni(I), Ni(II), and Ni(III) analogues provides access to a Ni(III) methyl complex via oxidative addition
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A structurally persistent bis-amido ligand framework capable of supporting nickel compounds in three different oxidation states has been identified. A highly unusual, isolable Ni(III) alkyl species has been prepared and characterized via a rare example of a two-electron oxidative addition of MeI to Ni(I).
- Lipschutz, Michael I.,Yang, Xinzheng,Chatterjee, Ruchira,Tilley, T. Don
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- Intrinsic Reactivity of Magnesium Surfaces toward Methyl Bromide
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The chemisorption and subsequent decomposition of methyl bromide on a Mg(0001) single-crystal surface is found to lead cleanly to the formation of a surface bromide and gas-phase hydrocarbon products including ethane.Stable surface alkyls are not observed even at temperatures as low as -150 deg C.Co-adsorbed dimethyl ether does not perturb this reactivity pattern.The formation of either a thin surface bromide or a surface oxide passivates this material to further reaction under UHV conditions.The implications of these results with respect to the mechanisms of carbon-halogen bond cleavage on magnesium and the formation of Grignard reagents are discussed.
- Nuzzo, Ralph G.,Dubois, Lawrence H.
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- High-Performance Catalysts Derived from Cupric Subcarbonate for Selective Hydrogenation of Acetylene in an Ethylene Stream
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A high-performance base metal catalyst for acetylene selective hydrogenation was prepared from cupric subcarbonate (Cu2(OH)2CO3) by thermal treatment with an acetylene-containing gas followed by hydrogen reduction. The characterization results revealed that the copper catalyst was composed of interstitial copper carbide (CuxC) and metal Cu, which were embedded in porous carbon matrix. The CuxC crystallites, which showed outstanding hydrogenation activity, were derived from the hydrogen reduction of copper (II) acetylide (CuC2) which was generated from the reaction between acetylene and Cu2(OH)2CO3. The Cu particles and porous carbon were generated from the unavoidable thermal decomposition of CuC2. The prepared Cu-derived catalyst completely removed the acetylene impurity in an ethylene stream with a very low over-hydrogenation selectivity at 110 °C and atmospheric pressure. No obvious deactivation was observed in a 180-h test run. In the Cu-derived catalyst, CuxC served as the catalytic site for H2 dissociation, Cu mainly functioned as the site for selective hydrogenation of acetylene, whereas the porous carbon matrix posed a steric hindrance effect on the chain growth of linear hydrocarbons so as to suppress the undesired oligomerization.
- Lu, Chenyang,Zeng, Aonan,Wang, Yao,Wang, Anjie
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- Peroxide Anions as Possible Active Species in Oxidative Coupling of Methane
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Oxidative coupling of CH4 forming C2H6 and C2H4 proceeded smoothly upon contact with Na2O2, BaO2, and SrO2 at low temperature below 673 K.This indicates that O22- ions are very reactive for activation of CH4.O2- ions contained in the peroxides did not activate CH4.
- Otsuka, Kiyoshi,Jinno, Kiyotaka,Komatsu, Takayuki
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- Photooxidation of Ethyl Iodide at 22 deg C
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C2H5I was photolized at 313 nm and 22 deg C in the presence of either I2, (C2H5)2NOH, or O2-He mixtures.We have determined that the quantum yields for the primary processes C2H5I + hυ -> C2H5 + I (3a) and C2H5I + hυ -> C2H4 + HI (3b) are Φ3a = 0.31 +/- 0.01 and Φ3b = 0.0095 +/- 0.0005.An upper limit for the rate coefficient for the following reaction has been found to be 1 x 1E-14 cm3/(molecule s) at 22 deg C: C2H5 + O2 -> C2H4 + HO2 (1).
- Shepson, Paul B.,Heicklen, Julian
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- A kinetics study for the oxidative coupling of methane on a Mn/Na 2WO4/SiO2 catalyst
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This paper presents an experimental kinetic study for the oxidative coupling of methane (OCM) over a Mn/Na2WO4/SiO2 catalyst prepared by incipient wetness impregnation. Because the catalyst is a reducible metal oxide, the stability of the catalyst has been assessed by Thermo Gravimetric Analysis (TGA). These experiments show that the catalyst has to be pre-treated with oxygen in order to obtain high C2 selectivity (around 85%) and that a low oxygen partial pressure during the OCM reactions is already sufficient to maintain the catalyst stable in the oxidized state. The catalyst has subsequently been tested in a micro-catalytic fixed bed reactor. The overall reaction orders and rate constants of the primary reactions were determined by measuring the intrinsic reaction rates at different methane and oxygen inlet concentrations. It was found that the reaction order in oxygen for the coupling reaction is 0.38, while the reaction order in oxygen for ethylene oxidation approaches unity, indicating that low oxygen concentration levels are beneficial for obtaining a high C2 selectivity (up to 80-90%). Such a low oxygen concentration can be obtained with distributive feeding in a membrane reactor. Based on the experiments and least-squares minimization, a simplified reaction mechanism is proposed, where the dependency of the ethane (coupling) and carbon dioxide (oxidation) production rates and the secondary ethylene production and C2 oxidation rates can be described with power-law type reaction rate expressions.
- Tiemersma,Tuinier,Gallucci,Kuipers,Annaland, M. Van Sint
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- Transformation of chlorinated organic compounds by iron and manganese powders in buffered water and in landfill leachate
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Tetrachloroethylene was transformed by iron powder (4.1 g/L) in oxygen-free, HEPES-buffered (pH 7) water at 50°C with a half-life of 20 days. The only products observed were the reactive intermediate, trichloroethylene, and ethene and ethane. 1,1,1-Trichloroethane, 1,1-dichloroethylene, and tetrachloroethylene were transformed by iron at room temperature in both autoclaved buffered water and in two non-autoclaved landfill leachates. The pattern and degree of removal were similar in all cases. Dichloromethane, 1,1-dichloroethane, and 1,4-dichlorobenzene were also tested, but were not removed from any of the systems. If manganese rather than iron was used, the substrates transformed depended upon the aqueous phase. Some biological transformations were seen in Leachate 2, but the activity was reduced by manganese and completely suppressed by iron.
- Schreier, Cindy G.,Reinhard, Martin
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- Group 5A Metal Oxides as Promoters for Oxidative Coupling of Methane
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Group 5A metal oxides were tested as promoters for oxidative coupling of methane.They were effective promoters for the coupling reaction, when mixed with 1A, 1A/2A, and 1A/3A oxide catalysts, respectively.Addition of Group 5A metal increased the activity
- Yamamura, Masami,Okado, Hideo,Tsuzuki, Naohide
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- BaCO3-supported vanadium oxide catalysts for the oxidative coupling of methane
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BaCO3-supported vanadium oxide catalysts, which consist of BaCO3 and small amounts of a barium orthovanadate Ba3(VO4)2 phase, exhibit high catalytic activity for oxidative coupling of methane, with particularly high activity for ethene and ethane production.
- Dang, Zhongyuan,Gu, Jingfang,Lin, Jingzhi,Yang, Dexing
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- Reactions of C2H5 radicals with HBr and Br at 298 K and millitorr pressures
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The rates of the reactions of ethyl radicals with HBr (k7) and with Br atoms (k8) have been measured at 298 K and millitorr pressures using the Very Low Pressure Reactor (VLPR) technique. The rate constants at 298 K are the following: k7 = (6.67 ± 0.14) × 10-13 cm3/(molecule's) and k8 = (1.19 ± 0.04) × 10-11 cm3/(molecule's). Reaction 7 is a factor of about 14 times slower than had been reported in the only other two direct measurements made (Nicovich, J. M. et al. J. Phys.Chem. 1991, 95, 9890. Seakins, P. W. et al. J. Phys Chem. 1992, 98, 9847) which also reported a negative activation energy for k7 of from -0.8 to -1.1 kcal/mol. Using broadly accepted thermochemistry for reaction 7 and reported values for the reverse reaction, it is shown that all reported data give a positive activation energy for k7.
- Dobis, Otto,Benson, Sidney W.
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- Silicon-Carbon Bond Formation Kinetics: Study of the Reactions of CH3 with SiH3, Si(CH3)3, and SiCl3
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The kinetics of three Si-C bond-forming association reactions were investigated at the high-pressure limit: SiH3 + CH3 (1), Si(CH3)3 + CH3 (2), and SiCl3 + CH3 (3).Rate constants were measured using a heatable tubular reactor coupled to a photoionization mass spectrometer.The two radical reactants were produced simultaneously (CH3 always in great excess) using pulsed 193-nm photolysis of suitable precursors diluted in helium, and the radical decays were monitored in time-resolved experiments.The radical decay profiles were fitted to appropriate expressions to obtain the desired rate constants.Reaction 1 was studied between 301 and 526 K yielding the following Arrhenius expression for the association reaction: k1 = (5.6 +/- 2.4) * 10-11 exp((3.0 +/- 1.6) kJ mol-1 / RT). (All rate constants are in the units cm3 molecule-1 s-1.) Reaction 2 was investigated between 306 and 526 K yielding the expression k2 = (5.2 +/- 2.2) * 10-11 exp((2.4 +/- 1.4) kJ mol-1 / RT).Reaction 3 was studied at one temperature, 303 K, where k3 = (1.1 +/- 0.4) * 10-10.Treating these association reactions as cross-combination reactions, the measured rate constants were found to be predicted with reasonable accuracy using the geometric mean rule and the rate constants of the related self-association reactions of the reactant radicals.The mechanisms of these reactions are discussed.
- Niiranen, Jukka T.,Gutman, David
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- Selective Synthesis of Ethylene by Dehydrogenative Coupling of Methane by Use of Thermal Diffusion Column
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Ethylene was found to be obtained dehydrogenatively from methane in extremely high selectivities (91.5percent at 9.4percent conversion of methane) with the downward introduction to the modified thermal diffusion column with electrically heated tungsten wire at 1200 deg C.
- Yamaguchi, Tatsuaki,Saito, Chiaki
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- Coordination chemistry of the tetrakis(2-hydroxyphenyl)ethene support mimic - Polymetallic magnesium, aluminum, and titanium derivatives
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The crystal structures of magnesium, aluminum, and titanium coordination complexes of the structurally preorganized tetrakis(2-hydroxyphenyl)ethene are reported. As a result of the absence of steric shielding and the conformational flexibility of the ligand, pseudo-dimeric complexes are formed instead of crown- or raft-like compounds. The unsubstituted tetrakis(2-hydroxyphenyl)ethene ligand thus emulates the complexation characteristics of the sterically open calix[4]arene system.
- Verkerk, Udo H.,McDonald, Robert,Stryker, Jeffrey M.
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- The study of supported manganese catalysts in the course of the oxidative coupling of methane
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The effect of the process parameters on the yield of the main products, ethane and ethylene, was studied for the methane oxidative dimerization over manganese catalysts deposited on solid carrying agents. The effect of various factors defining activity of manganese systems on their properties was analyzed. The best carrying agent for the catalytic system under study was chosen, and the optimal contents of an active component and a promoting additive providing a high yield of C2 hydrocarbons were determined.
- Kulichkov,Semikin,Kuzichkin,Lisitsyn
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- Surface processes in the catalytic oxidative coupling of methane to ethane
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Recent results on surface reaction steps in the oxidative coupling of methane (OCM) obtained from (1) transient experiments and (2) a microkinetic analysis are summarized.The interaction of methane and oxygen with MgO and Sm2O3 surfaces was investigated by applying H/D- and oxygen-isotope-exchange reactions.The role of short-lived adsorbed oxygen species in methane activation and product formation over MgO and Sm2O3 catalysts is discussed.Furthermore, elementary reaction steps and their rate constants are derived for the oxidative conversion of methane to COx and ethane from kinetic data for different (CaO)x(CeO2)1-x catalysts; the rate constants are related to the solid's properties, i.e., electron and O(2-) conductivity.
- Buyevskaya, Olga,Wolf, Dorit,Baerns, Manfred
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- Oxidative Coupling of Methane over Tin-containing Rare-earth Pyrochlores
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Rare-earth pyrochlores of general formula Ln2Sn2O7 (Ln=rare-earth) are found to be active catalysts for the oxidative coupling of methane, with enhanced conversion to useful hydrocarbons, particularly ethene, being observed at 1150 K for those rare-earths
- Ashcroft, Alexander T.,Cheetham, Anthony K.,Green, Malcolm L. H.,Grey, Clare P.,Vernon, Patrick D. F.
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- Reactions of Ethanethiol on Mo(110): Formation and Decomposition of a Surface Alkyl Thiolate
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The reactions of ethanethiol C2H5SH on Mo(110) under ultrahigh vacuum have been investigated by temperature-programmed reaction, X-ray photoelectron, and high-resolution electron energy loss spectroscopies.Electron energy loss spectroscopy indicates that the S-H bond in ethanethiol dissociates below 120 K to form a surface ethyl thiolate (C2H5S).At low coverages the ethyl thiolate decomposes to atomic carbon, atomic sulfur, and gaseous H2, with decomposition complete below 350 K.At high coverages, the surface thiolate decomposes during temperature-programmed reaction via three competing pathways: hydrogenolysis at 300 K to gaseous ethane, dehydrogenation at 340 K to gaseous ethylene, and decomposition to surface carbon, surface sulfur, and gaseous dihydrogen.Notably, the presence of surface atomic sulfur is not necessary for selective formation on clean Mo(110): the thiolate remains intact up to the temperature of hydrogenolysis onset.The last pathway proceeds via a hydrocarbon fragment(s) which decomposes at 570 K to gaseous H2 and atomic carbon.At saturation, ca. 75percent of all irreversibly chemisorbed ethanethiol forms gaseous hydrocarbons.The coverage-dependent kinetics for ethanethiol decomposition are discussed in terms of electronic and site-blocking effects.
- Roberts, Jeffrey T.,Friend, C. M.
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- Kinetics and mechanism of ethylene hydrogenation poisoned by CO on silica-supported monodisperse Pt nanoparticles
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The influence of particle size on the poisoning of ethylene hydrogenation by CO was studied over a series of catalysts composed of nearly monodisperse Pt nanoparticles (1.7-7.1 nm) encapsulated in mesoporous silica (SBA-15). The turnover frequency at 403 K in the presence of 0.5 Torr CO was ~2 × 10-2 s-1 (compared with ~102 s-1 in the absence of CO). The apparent activation energy in the absence and presence of 0.2 Torr CO was ~10 and 20 kcal mol-1, respectively. The pressure dependency changes significantly in the presence of CO; reaction orders in hydrogen were 1/2 in the presence of CO at 403 K and noncompetitive with regard to co-adsorption with C2H4. In the absence of CO at similar temperatures, H2 adsorption was primarily irreversible (first-order dependence), and H2 and C2H4 compete for the same sites. Ethylene orders at 403 K were first order in the presence of 0.2 Torr CO and remained unity with increasing CO pressure. At similar reaction conditions in the absence of CO, ethylene had an inhibitory effect (negative reaction order) on the overall hydrogenation reaction. The change in C2H4 and H2 kinetics suggests strong competitive adsorption between C2H4 and CO for the same type of site, whereas H2 apparently adsorbs on distinct surface sites due either to steric hindrance or H2-induced CO desorption. Incorporation of a quasi-equilibrated CO adsorption step into a noncompetitive Langmuir-Hinshelwood mechanism predicts the experimentally observed pressure dependencies and a doubling of the apparent activation energy. Hydrogenation of ethylene in the presence of 1 Torr CO was examined under reaction conditions at 403 K by infrared spectroscopy; the only surface species identified under reaction conditions was linear-bound CO. The hydrogenation of ethylene on clean Pt catalysts was structure-insensitive and remains insensitive in the presence of CO; rates decreased only by a factor of two with increasing particle size.
- Rioux, Robert M.,Komor, Russell,Song, Hyunjoon,Hoefelmeyer, James D.,Grass, Michael,Niesz, Krisztian,Yang, Peidong,Somorjai, Gabor A.
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- Oxidative Coupling of Methane with Alkaline Earth Halide Catalysts Supported on Alkaline Earth Oxides
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Halides of alkaline earth metal oxides such as MgCl2 or CaCl2 on CaO or on MgO were found to be excellent catalysts for the oxidative coupling of methane.The selectivity of C2 hydrocarbon reached 87percent at 750 deg C and CH4/O2=9.
- Fujimoto, Kaoru,Hashimoto, Shigeru,Asami, Kenji,Tominaga, Hiro-o
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- Oxidative Coupling of Methane over BaO Mixed with CaO and MgO
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Various metal oxides mixed with BaO were studied as a catalyst for coupling of methane.For example, a BaO-CaO catalyst shows a high activity (20.9 mmol/hg) for the C2 formation (C2H6+C2H4) with a high C2 selectivity (61.1percent) under the following conditions; 1073 K, P(CH4)=40 kPa, a ratio of CH4 to O2 = 5.0, and W/F = 3.39 gh/mol.
- Yamagata, Nobutsugu,Tanaka, Katsutoshi,Sasaki, Shoichi,Okazaki, Susumu
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- Bacterial Organomercurial Lyase: Novel Enzymatic Protonolysis of Organostannanes
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Pure bacterial organomercurial lyase has been found to catalyze a protonolytic cleavage of the carbon-tin bond in certain organostannanes.Of the compounds tested tetravinyltin is turned over with the highest specific activity, yielding ethylene as the organic product.Similarly, triethylvinyltin undergoes turnover by the lyase to yield ethylene and ethane in a 97:3 ratio, at 1/60th the rate of tetravinyltin turnover.Finally, tetramethyltin and trimethyltin fluoride yield small amounts of methane (2-5 turnovers/mol of enzyme) prior to eventual loss of enzyme activity.The decrease in activity observed during turnover of the organostannanes is consistent with the observed inhibition of the enzyme by dimethyltin dibromide.
- Walts, Alan E.,Walsh, Christopher T.
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- Acetylene Hydrogenation to Ethylene in a Hydrogen-Rich Gaseous Mixture on a Pd/Sibunit Catalyst
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Abstract: The reaction of the gas-phase hydrogenation of acetylene on a Pd/Sibunit catalyst was studied depending on the H2 : C2H2 molar ratio, the process temperature, and the presence of carbon monoxide. It was shown that for the reaction mixture of the composition H2 : C2H2 2 : C2H2 > 20, on the contrary, the order in hydrogen becomes zero and the reaction rate is determined by the acetylene content in the reaction mixture. It was found that an increase in the reaction temperature (from 30 to 85°C) leads to an increase in the contribution of complete hydrogenation to ethane. The introduction of CO into the reaction mixture up to a molar ratio of CO : C2H2 = 0.1 is accompanied by the almost complete blocking of the C2H4 readsorption sites, which results in a sharp increase in ethylene selectivity from 4 to 73%. With a further increase in the CO : C2H2 ratio, the number of sites available for hydrogen adsorption gradually decreases, and, correspondingly, the conversion decreases.
- Shlyapin,Glyzdova,Afonasenko,Temerev,Tsyrul’nikov
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- The Protolysis of Hexanes over a USHY Zeolite
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Detailed information gathered on the cracking of five hexane isomers has revealed major differences in the mechanisms of cracking in the individual isomers and suggests the possibility that synergistic effects play a role in the cracking of mixtures of hydrocarbons.We find that both n-hexane and 2,2-dimethylbutane do not crack via the chain process to any significant extent, presumably due to the absence of tertiary hydrogens in both molecules.On the other hand, 2,3-dimethylbutane, with two tertiary hydrogens, cracks readily via a chain process.The two monomethyl pentanes illustrate the fact that tertiary hydrogens are not all the same in terms of reactivity. 3-methylpentane has a much more reactive hydrogen than 2-methylpentane, with the result that more of this feed is converted by chain processes.However, the overall rate of conversion is higher in 2-methylpentane and lower in 2,3-dimethylbutane.It seems that, when it comes to maximizing the overall rate of reaction, the dominant influence is the rate of initiation by protolysis.In this work we examine the initiating protolysis reactions of the partent hexane molecules.These reactions start the chain processes which, in various measures, are responsible for the observed overall conversion in "catalytic cracking".We find that the rates and modes of the various protolysis reactions are profoundly different in the five isomeric hexanes.In discussing this fact we raise the issue of the significance of "test reactions" in catalyst evaluation.
- Bassir, M.,Wojciechowski, B. W.
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- Efficient Polyester Hydrogenolytic Deconstruction via Tandem Catalysis
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Using a mechanism-based solvent-free tandem catalytic approach, commodity polyester plastics such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polyethylene naphthalate (PEN) are rapidly and selectively deconstructed by combining the two air- and moisture-stable catalysts, Hf(OTf)4 and Pd/C, under 1 atm H2, affording terephthalic acid (or naphthalene dicarboxylic acid for PEN) and ethane (or butane for PBT) in essentially quantitative yield. This process is effective for both laboratory grade and waste plastics, and comingled polypropylene remains unchanged. Combined experimental and DFT mechanistic analyses indicate that Hf(OTf)4 catalyzes a mildly exergonic retro-hydroalkoxylation reaction in which an alkoxy C?O bond is first cleaved, yielding a carboxylic acid and alkene, and this process is closely coupled to an exergonic olefin hydrogenation step, driving the overall reaction forward.
- Kratish, Yosi,Marks, Tobin J.
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supporting information
(2021/12/22)
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- Investigation on the Thermal Cracking and Interaction of Binary Mixture of N-Decane and Cyclohexane
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Abstract: The investigation about the thermal cracking performance and interaction of different components in hydrocarbon fuels is of great significance for optimizing the formulation of high-performance hydrocarbon fuels. In this work, thermal cracking of n-decane, cyclohexane and their binary mixture were studied in a tubular reactor under different temperatures and pressures. The gas and liquid products were analyzed in detail with different gas chromatography. The main gas products of pure n-decane and cyclohexane are similar, and there is a certain difference in the main liquid products. For binary mixture, the overall conversion rate and gas yield are lower than their theoretical value. The cracking conversion rate of n-decane in binary mixture is lower than that in pure n-decane, but the opposite change occurs for cyclohexane, and the effect become more obvious as the increase of the reaction pressure. These experimental phenomena can be explained by bond dissociation energy and free radical reaction mechanism. The pressure affects the free radical reaction path, and high pressure is more conducive to bimolecular hydrogen abstraction reaction, which will lead to different product content. A law of interaction between the n-decane and cyclohexane was observed according to the experimental results. [Figure not available: see fulltext.]
- Chen, Xuejiao,Pang, Weiqiang,Wang, Bo,Zhang, Ziduan,Zhou, Lingxiao,Zhu, Quan
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- Conversion of Phenol and Lignin as Components of Renewable Raw Materials on Pt and Ru-Supported Catalysts
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Hydrogenation of phenol in aqueous solutions on Pt-Ni/SiO2, Pt-Ni-Cr/Al2 O3, Pt/C, and Ru/C catalysts was studied at temperatures of 150–250? C and pressures of 40–80 bar. The possibility of hydrogenation of hydrolysis lignin in an aqueous medium in the presence of a Ru/C catalyst is shown. The conversion of hydrolysis lignin and water-soluble sodium lignosulfonate occurs with the formation of a complex mixture of monomeric products: a number of phenols, products of their catalytic hydrogenation (cyclohexanol and cyclohexanone), and hydrogenolysis products (cyclic and aliphatic C2 –C7 hydrocarbons).
- Bobrova, Nataliia A.,Bogdan, Tatiana V.,Bogdan, Viktor I.,Koklin, Aleksey E.,Mishanin, Igor I.
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- Symmetry-Broken Au–Cu Heterostructures and their Tandem Catalysis Process in Electrochemical CO2 Reduction
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Symmetry-breaking synthesis of colloidal nanocrystals with desired structures and properties has aroused widespread interest in various fields, but the lack of robust synthetic protocols and the complex growth kinetics limit their practical applications. Herein, a general strategy is developed to synthesize the Au–Cu Janus nanocrystals (JNCs) through the site-selective growth of Cu nanodomains on Au nanocrystals, which is directed by the substantial lattice mismatch between them, with the assistance of judicious manipulation of the growth kinetics. This strategy can work on Au nanocrystals with different architectures for the achievement of diverse asymmetric Au–Cu hybrid nanostructures. Of particular note, the obtained Au nanobipyramids (Au NBPs)-based JNCs facilitate the conversion of CO2 to C2 hydrocarbon production during electrocatalysis, with the Faradaic efficiency and maximum partial current density being 4.1-fold and 6.4-fold higher than those of their monometallic Cu counterparts, respectively. The excellent electrocatalytic performances benefit from the special design of the Au–Cu Janus architectures and their tandem catalysis mechanism as well as the high-index facets on Au nanocrystals. This research provides a new approach to synthesize various hybrid Janus nanostructures, facilitating the study of structure-function relationship in the catalytic process and the rational design of efficient heterogeneous electrocatalysts.
- Jia, Henglei,Yang, Yuanyuan,Chow, Tsz Him,Zhang, Han,Liu, Xiyue,Wang, Jianfang,Zhang, Chun-yang
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- Coupling conversion of methane with carbon monoxideviacarbonylation over Zn/HZSM-5 catalysts
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Efficient direct transformation of methane into value-added chemicals has great significance for long-term sustainability of fuels and chemicals, but remains a major challenge due to its high inertness. Reported here is that methane can be activated effectivelyviacarbonylation with CO over Zn/HZSM-5 catalysts under mild conditions. The selectivity to aromatics alone reaches 80% among all hydrocarbon products at 823 K, whereas as high as 92% ethane selectivity is achieved at a lower temperature of 673 K.13CO isotope labelling experiments demonstrate that approximately 50% of the carbon atoms in all the products originate from carbon monoxide, whereas another half of the carbons come from methane, indicating that the precursors of hydrocarbon products are acyl compounds and/or acetic acid formed by carbonylation of methane with carbon monoxide. This provides potential for transformation of methane into value-added chemicals under mild reaction conditions.
- Wen, Fuli,Zhang, Jin,Chen, Zhiyang,Zhou, Ziqiao,Liu, Hongchao,Zhu, Wenliang,Liu, Zhongmin
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p. 1358 - 1364
(2021/03/14)
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- Role of Ga3+promoter in the direct synthesis of iso-butanolviasyngas over a K-ZnO/ZnCr2O4catalyst
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The direct synthesis of iso-butanol is an important reaction in syngas (composed of CO and H2) conversion. K-ZnO/ZnCr2O4(K-ZnCr) is a commonly used catalyst. Here, Ga3+is used as an effective promoter to boost the efficiency of the catalyst and retard the production of CO2. X-ray diffraction, X-ray photoelectron spectroscopy, ultraviolet-visible diffuse reflection spectroscopy and electron microscopy were used to characterize the structural variations with different amounts of Ga3+, the results showed that the particle size of the catalyst decreases with the addition of Ga3+. The temperature-programmed desorption of NH3and CO2, and diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTs) analysis of the CO adsorption revealed that the acidity and basicity were altered owing to the different forms of Ga3+adoption. X-ray photoelectron spectroscopy and density functional theory (DFT) calculations revealed that the formation of Ga clusters that are coordinated on the exposed surfaces of ZnCr2O4, and undergo a tetra-coordinated Ga3+exchange with one of the Zn in ZnCr2O4(ZG) and ZnGa2O4, probably depends on the amount of Ga added. The structural evolution of the Ga3+promoted K-ZnO/ZnCr2O4catalysts can be described as follows: (i) the main forms are ZG and Ga coordinated ZnCr2O4, in which the amount of Ga3+is below 1.10 wt%; and (ii) the Ga3+containing compound is gradually changed from ZG to ZnGa2O4and the amount of gallium clusters increased when the amount of Ga3+was higher than 1.10 wt%. The catalytic performance evaluation results show that K-Ga1.10ZnCr exhibits the highest space time yield and selectivity of alcohols, in which the three compounds play different roles in syngas conversion: ZG is the main active site that boosts the efficiency of the catalysts, owing to the intensified CO adsorption and decreased activation energy of CHO formation through CO hydrogenation; ZnGa2O4only modifies the surface basicity and acidity on the catalyst, thereby impacting the carbon chain growth after the CO is adsorbed. The effects of Ga coordinated with ZnCr2O4shows little impact on the CO adsorption owing to the weak electron donating effects of Ga.
- Zhang, Tao,Zeng, Chunyang,Wu, Yingquan,Gong, Nana,Yang, Jiaqian,Yang, Guohui,Tsubaki, Noritatsu,Tan, Yisheng
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p. 1077 - 1088
(2021/02/26)
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- Transformation synthesis of SSZ-13 zeolite from ZSM-35 zeolite
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Interzeolite conversion as a promising alternative strategy for zeolite synthesis has received extensive attention. It is of great significance to understand the potential rules of conversion between zeolites with different topologies for effective regulation of zeolite synthesis. Hydrothermal conversion of ZSM-35 (FER-type) zeolite containing the mor composite building units into SSZ-13 zeolite (CHA-type) using N,N,N-trimethyl-1-adamantammonium hydroxide (TMAdaOH) as template was performed for the first time. The effects of TMAdaOH/SiO2 ratio, Na2O/SiO2 ratio, the additional starting zeolite and crystallization time on the interzeolite conversion of ZSM-35 into SSZ-13 were investigated. The interzeolite conversion mechanism concerning the synthesis of SSZ-13 from ZSM-35 zeolite was proposed and verified by DFT calculation. The results of DFT calculations suggested that ZSM-35 zeolite with mor composite building unit had the potential to decompose into 6-Membered Rings, and further transform into CHA-type zeolite containing d6r composite building unit. Therefore, zeolites containing mor structure have the potential to be converted into zeolites containing d6r structure.
- Bing, Liancheng,Cong, Wenwen,Han, Dezhi,Li, Kexu,Li, Qiang,Wang, Fang,Wang, Guangjian,Xu, Changyou
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- Methane coupling and hydrogen evolution induced by palladium-loaded gallium oxide photocatalysts in the presence of water vapor
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Non-oxidative coupling of methane (NOCM, 2CH4 → C2H6 + H2) is a reaction that can directly produce ethane and hydrogen at the same time, and gallium oxide (Ga2O3) powder has been reported as an effective photocatalyst for NOCM at room temperature. In this study, we investigated the reaction conditions for Pd-loaded Ga2O3 photocatalysts to improve the production rate of C2H6 and H2. We found that the 0.1 wt% Pd/Ga2O3 exhibited high selectivity of C2H6 (75.8%, carbon-based) under the conditions of steam reforming of methane. Photocatalytic NOCM seems to proceed in the presence of small amount of water. An increase in water vapor pressure (PH2O) was essential for the steady production of C2H6 and H2. The C2H6 production rate was 0.79 μmol min?1 for 50 mg of Pd/Ga2O3 powder at PH2O = 3.6 kPa. The apparent quantum efficiency (AQE) for C2H6 production was 5.1%, which is much higher than that of conventional photocatalytic NOCM in the absence of water vapor. The importance of water adsorbates on the photocatalyst surface was suggested by water vapor adsorption isotherm and Fourier transform infrared (FT-IR) spectroscopy. It is revealed that multilayered water molecules adsorbed on the photocatalyst surface play a role as a reaction field that promotes the dehydrogenative coupling of CH4.
- Ishimaru, Mizuki,Amano, Fumiaki,Akamoto, Chiho,Yamazoe, Seiji
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p. 192 - 200
(2021/04/27)
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- Continuous methane to ethane conversion using gaseous oxygen on ceria-based Pd catalysts at low temperatures
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Methane upgrading into more valuable chemicals has been a promising challenge. It was previously reported that highly oxidized Pd/CeO2 could produce ethane from methane. Here, we enhanced the ethane productivity by controlling oxygen mobility of the catalyst support and adding water adsorbents. Pd/Ce1-xPdxO2-y catalyst, in which Pd atom was doped at the ceria support, showed enhanced oxygen activation and oxygen transfer, improving the ethane productivity from 0.04 molC2H6/mmolSurfacePd/h in Pd/CeO2 to 0.57 molC2H6/mmolSurfacePd/h in Pd/Ce1-xPdxO2-y. In order to remove the water produced from methane oxidation, zeolite 13X was physically mixed with Pd/Ce1-xPdxO2-y. The water adsorbent could increase the ethane production significantly, especially at low temperatures. The ethane yield of 0.30 % could be obtained at 290 °C using gaseous O2 as an oxidant. This work can provide useful ways to enhance the yield of value-added products in oxidative methane conversion.
- Kim, Gunjoo,Kwon, Gihun,Lee, Hyunjoo
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- Light-Induced Nonoxidative Coupling of Methane Using Stable Solid Solutions
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Achieving efficient and direct conversion of methane under mild conditions is of great significance for innovations in the chemical industry. However, the efficiency and lifetime of most catalysts remain too far from practical requirements, since it is difficult to break the first C?H bond of methane as well as to suppress the following complete dehydrogenation (or overoxidation) and the resulting carbonaceous deposition (or CO2). Here, we report that wurtzite GaN:ZnO solid solutions exhibit unique and unprecedented photocatalytic performances for the nonoxidative coupling of methane at room temperature, exclusively generating ethane with nearly stoichiometric H2. High conversion rate (>330 μmol g?1 h?1), long-term stability (>70 h), and superior coke-resistance were achieved. At 293 K, the methane conversion exceeds 7 %, comparable to the equilibrium conversion of thermal catalysis at 910 K. Mechanistic studies revealed that the N-ZnGa-ON units and the absence of acid sites on the surface played crucial roles in reactivity and coke resistance, respectively.
- Li, Jiayang,Li, Lu,Mu, Xiaowei,Mu, Xiaoyue,Qian, Yumeng,Wang, Guangming,Zhan, Qingyun
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supporting information
p. 20760 - 20764
(2021/08/13)
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- Exploring the formation of carbonates on La2O3catalysts with OCM activity
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La2O3 catalyzed oxidative coupling of methane (OCM) is one of the promising catalytic partial oxidation processes that converts methane directly into more valuable C2 products. Previous optimization studies found a nanorod shape La2O3 sample (n-La2O3) to exhibit the best low temperature OCM activity. Our previous results correlated the formation of bulk La2O2CO3 with a poisoning effect in OCM. In this study, coupled online MS and in situ XRD are applied to further elucidate this poisoning effect. In the same temperature range, the n-La2O3 sample is compared with a commercial isotropic La2O3 (M-La2O3) catalyst for their OCM performance and propensity to form La2O2CO3 under various CO2 concentrations. The n-La2O3 sample is found to be far more resistant against forming La2O2CO3 than the M-La2O3 sample. In situ XRD results show that after identical exposures to 10%, 30%, and 50% CO2 at around 550 °C, the phase transition to La2O2CO3 is complete for M-La2O3, while n-La2O3 is only partially converted. In addition, coupled online MS and in situ XRD results indicate that the n-La2O3 sample is able to maintain larger grain sizes of La2O3 than the M-La2O3 sample after the same adsorption amount of CO2. Arrhenius plots confirm that in the same temperature range the apparent activation energy for OCM is around 60 kJ mol-1 lower for n-La2O3 than for M-La2O3. These results strongly support that carbonate formation suppresses the OCM performance, which may serve as an indicator in developing more efficient La2O3 based catalysts.
- Guan, Cairu,Liu, Zebang,Pang, Yaoqi,Van Bavel, Alexander P.,Vovk, Evgeny,Wang, Danyu,Yang, Yong,Yu, Na,Zhou, Xiaohong
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p. 6516 - 6528
(2021/10/12)
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- Oxidative coupling of methane over Mo-Sn catalysts
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A novel Mo-Sn catalyst for the oxidative coupling of methane was designed using a hydrothermal method. At 650 °C, the conversion of methane was 8.6% and the selectivity of the C2 hydrocarbons reached as high as 98.1% over the Mo1Sn3 catalyst, with a CO2 selectivity of only 0.8%. We demonstrated that the deep oxidation of methane to CO2 was further inhibited due to the synergistic effects of moderately strong basic sites and reactive oxygen species on the catalyst surface. This journal is
- Gao, Xiujuan,Han, Yizhuo,Liu, Xiaoyan,Meng, Xianghai,Song, Faen,Tan, Yisheng,Wang, Xiaoxing,Yan, Lina,Zhang, Junfeng,Zhang, Qingde,Zhang, Tao
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supporting information
p. 13297 - 13300
(2021/12/17)
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- Heterogeneous 1H and 13C Parahydrogen-Induced Polarization of Acetate and Pyruvate Esters
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Magnetic resonance imaging of [1-13C]hyperpolarized carboxylates (most notably, [1-13C]pyruvate) allows one to visualize abnormal metabolism in tumors and other pathologies. Herein, we investigate the efficiency of 1H and 13C hyperpolarization of acetate and pyruvate esters with ethyl, propyl and allyl alcoholic moieties using heterogeneous hydrogenation of corresponding vinyl, allyl and propargyl precursors in isotopically unlabeled and 1-13C-enriched forms with parahydrogen over Rh/TiO2 catalysts in methanol-d4 and in D2O. The maximum obtained 1H polarization was 0.6±0.2 % (for propyl acetate in CD3OD), while the highest 13C polarization was 0.10±0.03 % (for ethyl acetate in CD3OD). Hyperpolarization of acetate esters surpassed that of pyruvates, while esters with a triple carbon-carbon bond in unsaturated alcoholic moiety were less efficient as parahydrogen-induced polarization precursors than esters with a double bond. Among the compounds studied, the maximum 1H and 13C NMR signal intensities were observed for propyl acetate. Ethyl acetate yielded slightly less intense NMR signals which were dramatically greater than those of other esters under study.
- Salnikov, Oleg G.,Chukanov, Nikita V.,Kovtunova, Larisa M.,Bukhtiyarov, Valerii I.,Kovtunov, Kirill V.,Shchepin, Roman V.,Koptyug, Igor V.,Chekmenev, Eduard Y.
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p. 1389 - 1396
(2021/05/31)
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- The effect of oxygen vacancy of alkaline-earth metal Sr doped Sm2Zr2O7 catalysts in the oxidative coupling of methane
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A series of the Sr/Sm2Zr2O7 catalysts with different Sr contents prepared by the coprecipitation method were used for OCM. The results revealed that the basicity and oxygen vacancies concentration on the surface of the Sm2Zr2O7 catalyst were notably increased because of the addition of Sr. Activation of O2 by the oxygen vacancies was responsible for the formation of C2. Specifically, the 7.6% Sr/Sm2Zr2O7 catalyst possessed 18.4% C2 yield at 750 °C due to the presence of moderate basicity and the highest ratio of the oxygen species O2– to lattice oxygen O2–. More importantly, the 7.6%Sr/Sm2Zr2O7 catalyst possessed high stability.
- Hao, Jie,Cai, Fufeng,Wang, Jiyang,Fu, Yu,Zhang, Jun,Sun, Yuhan
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- Unexpected activity of MgO catalysts in oxidative coupling of methane: Effects of Ca-promoter
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Unexpectedly, we founded very different catalytic activities of MgO in oxidative coupling of methane (OCM) depending on company that supplied the precursors, which was due to the Ca-related impurities. Accordingly, we investigated the effects of Ca-promoter on the catalytic activity of MgO catalysts. Substituting Ca into the MgO catalysts strongly influenced both the formation of oxygen vacancies and the base properties of surface lattice oxygen (Olat), which are key factors in this reaction. The formed oxygen vacancies resulted in high methane conversion through the facile conversion of methane to methyl radical, whereas Olat with medium basicity played an important role in producing ethylene through the facile dehydrogenation of ethane.
- An, Suna,Cho, JeongHyun,Jung, Ji Chul,Kwon, Dahye,Yang, Inchan
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- THERMAL OXIDATIVE COUPLING OF METHANE PROCESS USING RENEWABLE ENERGY WITH POSSIBLE CO-PRODUCTION OF HYDROGEN
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The disclosure relates in its first aspect to a process for converting methane into chemicals. The process comprises the steps of (a) providing a first stream (1; 7) comprising methane; (b) providing a second stream (13) which is an oxygen-rich stream; (c) contacting said first stream (1; 7) with said second stream (13) under oxidation reaction conditions to obtain a third stream (15) comprising chemicals and water; (d) performing at least one separation step on said third stream (15) to recover a water stream (21) and a fourth stream (39) comprising chemicals; (e) subjecting said water stream (21) to an oxidation reaction under first reaction conditions to produce at least an oxygen stream (29), wherein the oxygen stream (29) is recycled into the second stream (13). In its second aspect, the disclosure relates to an installation for working the process of the first aspect.
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(2021/12/30)
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- Morphology Effects of Nanoscale Er2O3 and Sr-Er2O3 Catalysts for Oxidative Coupling of Methane
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Abstract: Er2O3 nanorods were prepared by a hydrothermal method, and Sr-modified Er2O3 nanorods (Sr-Er2O3) were synthesized using an impregnation method. Their catalytic performance for oxidative coupling of methane was investigated. The catalysts were characterized by several techniques such as XRD, N2 adsorption, TEM, XPS, O2-TPD and CO2-TPD. Compared with Er2O3 and Sr-Er2O3 nanoparticles, Er2O3 and Sr-Er2O3 nanorods exhibit higher CH4 conversion and C2–C3 selectivity. This is caused by higher (O? + O2?)/O2? ratio, a higher number of chemisorbed oxygen species and moderate basic sites achieved on the nanorods catalysts. The Sr-Er2O3 nanorods afford a 23.2% conversion of CH4 with 50.3% selectivity to C2–C3 at 650?°C. Graphic Abstract: [Figure not available: see fulltext.]
- Fan, Yuqiao,Sun, Mingxing,Miao, Changxi,Yue, Yinghong,Hua, Weiming,Gao, Zi
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p. 2197 - 2206
(2021/01/04)
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- New Mechanistic and Reaction Pathway Insights for Oxidative Coupling of Methane (OCM) over Supported Na2WO4/SiO2 Catalysts
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The complex structure of the catalytic active phase, and surface-gas reaction networks have hindered understanding of the oxidative coupling of methane (OCM) reaction mechanism by supported Na2WO4/SiO2 catalysts. The present study demonstrates, with the aid of in situ Raman spectroscopy and chemical probe (H2-TPR, TAP and steady-state kinetics) experiments, that the long speculated crystalline Na2WO4 active phase is unstable and melts under OCM reaction conditions, partially transforming to thermally stable surface Na-WOx sites. Kinetic analysis via temporal analysis of products (TAP) and steady-state OCM reaction studies demonstrate that (i) surface Na-WOx sites are responsible for selectively activating CH4 to C2Hx and over-oxidizing CHy to CO and (ii) molten Na2WO4 phase is mainly responsible for over-oxidation of CH4 to CO2 and also assists in oxidative dehydrogenation of C2H6 to C2H4. These new insights reveal the nature of catalytic active sites and resolve the OCM reaction mechanism over supported Na2WO4/SiO2 catalysts.
- Baltrusaitis, Jonas,Fushimi, Rebecca R.,Kiani, Daniyal,Sourav, Sagar,Wachs, Israel E.,Wang, Yixiao
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p. 21502 - 21511
(2021/08/25)
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- Breaking the inverse relationship between catalytic activity and selectivity in acetylene partial hydrogenation using dynamic metal–polymer interaction
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The partial hydrogenation of acetylene impurities in ethylene is industrially important because acetylene acts as a catalyst poison in downstream ethylene polymerization processes. In this reaction, simultaneously achieving high acetylene conversion and partial hydrogenation selectivity is challenging, and most known catalyst systems exhibit an inverse activity–selectivity relationship. Here, an amorphous polyphenylene sulfide (Am-PPS) was synthesized as a promoter for 0.1 wt% Pd/α-Al2O3. The catalyst modification using a trace amount of Am-PPS (0.15 wt%) enabled a remarkable enhancement of ethylene selectivity without an appreciable loss in acetylene hydrogenation activity. This could be attributed to the dynamic change of the Am-PPS–Pd interface, which selectively allows the cooperative adsorption of acetylene and H2, but not ethylene. Besides, the modified catalyst exhibited excellent long-term stability because of the high thermochemical stability of the polymer. These results demonstrate the unique possibility of using dynamic metal–polymer interaction to design partial hydrogenation catalysts that simultaneously exhibit high activity, selectivity, and stability.
- Park, Younghwan,Lee, Songhyun,Hyun, Kyunglim,Lee, Jueun,Park, Jeong Young,Ryoo, Ryong,Choi, Minkee
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p. 716 - 725
(2021/10/14)
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- METHOD TO PRODUCE C4 OLEFINS FROM NATURAL GAS-DERIVED ACETYLENE
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In accordance with the purpose(s) of the present disclosure, as embodied and broadly described herein, the disclosure relates to a method for producing C4 olefins from acetylene using supported metal-based catalysts and metal-based promoters. The method is inexpensive, efficient, and environmentally sound. Additionally, the method is selective for C4 olefins and other value-added products based on changes to reaction parameters including temperature, feed gas composition, and promoter identity. This abstract is intended as a scanning tool for purposes of searching in the particular art and is not intended to be limiting of the present disclosure.
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-
Paragraph 0015; 0016; 0019; 0020; 0247
(2021/10/22)
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- STABLE, HIGH SELECTIVITY CATALYSTS AND CATALYST SYSTEMS, AND PROCESSES FOR THEIR USE
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The present invention relates to catalysts, catalyst systems, and processes for the production of valuable light olefins, such as C2-C4 olefins (ethylene, propylene, and/or butenes) from paraffinic hydrocarbons, such as propane, through dehydrogenation and metathesis. Some particular aspects relate to the discovery of non-precious metal catalysts and catalyst systems utilizing such catalysts, for example in the case of being in an admixture with a metathesis catalyst, which advantageously exhibit high performance in terms of activity, selectivity, and stability. Other advantages can include a reduced production of byproducts (e.g., methane and ethane) that result from undesired side reactions, in addition to benefits that may be attained through the addition of a sulfur-bearing compound (e.g., H2S).
- -
-
Paragraph 84-87; 104; 105
(2021/08/06)
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- Oxidative Cracking of Propane in the Presence of Hydrogen
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The effect of H2 additions to the initial mixture on the parameters of the oxidative cracking of propane at atmospheric pressure, temperatures of 500°C–750°C, reaction time of 2 s, and С3H8/О2 initial ratio ~2 was experimentally evaluated. Results revealed that small amounts of H2 promoted the process due to the formation of additional active radicals OH? and H?. Performance of the oxidative cracking of propane in a large excess of H2 led to an increase in the yield of methane and ethane, while the yield of ethylene, the target product of the process, decreased.
- Arutyunov, V. S.,Nikitin, A. V.,Ozerskii, A. V.,Sedov, I. V.,Timofeev, K. A.,Zimin, Ya. S.
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p. 787 - 792
(2021/08/13)
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- Dehydrogenation of Propane in the Presence of CO2 on Supported Monometallic MOy/SiO2 and CrOxMOy/SiO2 (M = Fe, Co, and Ni) Bimetallic Catalysts
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Abstract: An analysis is performed of the physicochemical properties of M/SiO2 (M = Fe, Co, and Ni) oxide monometallic and CrM/SiO2 (M = Fe, Co, and Ni) bimetallic catalysts supported on amorphous silica. The catalysts are characterized via TGA, XRD, UV–Vis diffuse reflectance spectroscopy, and SEM. Adding 1?wt?% of a second transition metal (Fe, Ni, and Co) to the 3% CrOx/SiO2 chromium oxide catalyst substantially raises the conversion of propane to 64% with a drop in the selectivity towards propylene and formation of methane as a main by-product in the case of nickel. Introducing iron and cobalt raises the selectivity towards propylene to 72% with a drop in the conversion of propane.
- Tedeeva,Kustov,Pribytkov,Strekalova,Kalmykov,Dunaev,Kustov
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- Synergistic effect of Fe and Ga incorporation into ZSM-5 to increase propylene production in the cracking ofn-hexane utilizing a microchannel reactor
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In the present study, the effect of various amounts of Fe and Ga in the catalytic cracking ofn-hexane in a microchannel reactor was investigated using experimental design by the D-optimal method. Nano zeolites incorporated with Fe and Ga metals were synthesized in a fluorine environment to investigate the synergistic effect of the metals on the textural and acidic properties of the catalysts, which ultimately improved the performance of the synthesized catalysts in the efficient production of light olefins, in particular propylene. Three synthesis parameters including the Si/Al, Si/Fe and Si/Ga ratios were considered as the main factors to determine the optimal conditions for obtaining the maximum conversion ofn-hexane, yield of light olefins, and P/E ratio and minimum yield of alkanes as the responses. In sample FeGa-1, the P/E ratio reached 3.97, indicating the significant effect of the substituted metals in improving the desirable routes for propylene production. According to the results of the acidic properties, Fe, Al and Ga increased the number of total acid sites and the strengths of strong and weak acid sites, respectively. In addition, according to the results obtained from sample FeGa-7, the synergistic effect of Fe and Ga increased the number of weak acid sites.
- Halimitabrizi, Parya,Rashidzadeh, Mehdi,Sakha, Mohsen Rostami,Salari, Darush,Soltanali, Saeed
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p. 13833 - 13846
(2021/08/16)
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- Pd-Modified ZnO-Au Enabling Alkoxy Intermediates Formation and Dehydrogenation for Photocatalytic Conversion of Methane to Ethylene
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Photocatalysis provides an intriguing approach for the conversion of methane to multicarbon (C2+) compounds under mild conditions; however, with methyl radicals as the sole reaction intermediate, the current C2+ products are dominated by ethane, with a negligible selectivity toward ethylene, which, as a key chemical feedstock, possesses higher added value than ethane. Herein, we report a direct photocatalytic methane-to-ethylene conversion pathway involving the formation and dehydrogenation of alkoxy (i.e., methoxy and ethoxy) intermediates over a Pd-modified ZnO-Au hybrid catalyst. On the basis of various in situ characterizations, it is revealed that the Pd-induced dehydrogenation capability of the catalyst holds the key to turning on the pathway. During the reaction, methane molecules are first dissociated into methoxy on the surface of ZnO under the assistance of Pd. Then these methoxy intermediates are further dehydrogenated and coupled with methyl radical into ethoxy, which can be subsequently converted into ethylene through dehydrogenation. As a result, the optimized ZnO-AuPd hybrid with atomically dispersed Pd sites in the Au lattice achieves a methane conversion of 536.0 μmol g-1 with a C2+ compound selectivity of 96.0% (39.7% C2H4 and 54.9% C2H6 in total produced C2+ compounds) after 8 h of light irradiation. This work provides fresh insight into the methane conversion pathway under mild conditions and highlights the significance of dehydrogenation for enhanced photocatalytic activity and unsaturated hydrocarbon product selectivity.
- Jiang, Wenbin,Low, Jingxiang,Mao, Keke,Duan, Delong,Chen, Shuangming,Liu, Wei,Pao, Chih-Wen,Ma, Jun,Sang, Shuaikang,Shu, Chang,Zhan, Xiaoyi,Qi, Zeming,Zhang, Hui,Liu, Zhi,Wu, Xiaojun,Long, Ran,Song, Li,Xiong, Yujie
-
supporting information
p. 269 - 278
(2021/01/12)
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- Multiple Cuprous Centers Supported on a Titanium-Based Metal-Organic Framework Catalyze CO2Hydrogenation to Ethylene
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Hydrogenation of carbon dioxide (CO2) to ethylene (C2H4) can be achieved in two routes via tandem reactions: (1) CO2hydrogenation to methanol (CH3OH) followed by methanol-to-olefin conversion and (2) reverse water-gas shift reaction followed by Fischer-Tropsch synthesis. Here we present another tandem route for CO2-to-C2H4conversion via (3) CO2hydrogenation to ethanol (C2H5OH) followed by C2H5OH dehydration. Multiple cuprous (CuI) centers were loaded onto the Ti8(μ2-O)8(μ2-OH)4secondary building units of a Ti-based metal-organic framework (MOF), MIL-125-NH2, via deprotonation and ion exchange of the μ2-OH groups. These multiple CuIcenters catalyzed CO2hydrogenation to C2H5OH, while the Ti2-μ2-O-M+(M+= H+, Li+) sites converted C2H5OH to C2H4. The MOF achieved CO2-to-C2H4generation rates of up to 2598 μmol gCat-1h-1in supercritical CO2(CO230 MPa, H25 MPa) at 85 °C and 514 μmol gCat-1h-1in the gas phase at 5 MPa (H2:CO2= 3) and 100 °C, respectively. This work opens another path to selectively producing C2H4via the hydrogenation of CO2
- An, Bing,Cao, Yonghua,Dai, Yiheng,Li, Han,Li, Zhe,Lin, Wenbin,Wang, Cheng,Wang, Yongke,Zeng, Lingzhen,Zhang, Jingzheng,Zhou, Yang
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p. 11696 - 11705
(2021/09/28)
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- Synthesis of a Boron–Imidazolate Framework Nanosheet with Dimer Copper Units for CO2 Electroreduction to Ethylene
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Fundamental understanding of the dependence between the structure and composition on the electrochemical CO2 reduction reaction (CO2RR) would guide the rational design of highly efficient and selective electrocatalysts. A major impediment to the deep reduction CO2 to multi-carbon products is the complexity of carbon–carbon bond coupling. The chemically well-defined catalysts with atomically dispersed dual-metal sites are required for these C?C coupling involved processes. Here, we developed a catalyst (BIF-102NSs) that features Cl? bridged dimer copper (Cu2) units, which delivers high catalytic activity and selectivity for C2H4. Mechanistic investigation verifies that neighboring Cu monomers not only perform as regulator for varying the reaction barrier, but also afford distinct reaction paths compared with isolated monomers, resulting in greatly improved electroreduction performance for CO2.
- Hong, Qin-Long,Shao, Ping,Wang, Wenjing,Yi, Luocai,Zhang, Hai-Xia,Zhang, Huabin,Zhang, Jian,Zheng, Lirong,Zhou, Wei
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p. 16687 - 16692
(2021/06/25)
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- CO2 hydrogenation to C5+ hydrocarbons over K-promoted Fe/CNT catalyst: Effect of potassium on structure–activity relationship
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Developing efficient catalysts for direct CO2 hydrogenation to fuel hydrocarbons is of great significance for the effective utilization of CO2, and C5+ selectivity is one critical indicator for the process economics. In this work, a series of K-promoted Fe/CNT catalysts were prepared by the co-impregnation method, and their catalytic performance for CO2 hydrogenation was studied in a slurry-bed reactor. As a result, CO2 conversion and C5+ selectivity showed positive correlation with the increase of K/Fe ratio from 0 to 0.3, but further increase of K/Fe ratio above 0.3 slightly affected its. The catalyst with a K/Fe molar ratio of 0.3 achieved the best performance with CO2 conversion of 23.7% and C5+ selectivity of 56%. In addition, the structure–activity relationship of the catalyst was discussed based on various characterization results. K-modified catalysts presented a higher specific surface area and stronger CO2 chemisorption, which helped to improve CO2 conversion and C5+ selectivity. However, excessive potassium loading caused a loss of specific surface area, reduction degree, and graphitization degree of the catalyst, which inhibited the CO2 chemisorption and the formation of C5+ hydrocarbons.
- Dai, Liya,Chen, Yao,Liu, Renjie,Li, Xin,Ullah, Niamat,Li, Zhenhua
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- Effect of sodium loading on Pt/ZrO2 during ethanol steam reforming
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Ethanol steam reforming (ESR) was investigated on unpromoted and several sodium promoted Pt/ZrO2 catalysts. From DRIFTS experiments, the following steps during ESR were inferred: dissociation of ethanol to produce ethoxy species; oxidative dehydrogenation of ethoxy species to acetate; and acetate decomposition. Acetate decomposition depends on the catalyst formulation. Decarboxylation is the most favored route at high sodium loading (2.5 and 5 wt.%); acetate decomposes in the forward direction to CH4 and a carbonate, which further decomposes to CO2. In contrast, decarbonylation is prevalent for the unpromoted catalyst or catalysts having low sodium loading. Acetate likely decomposes to CH3OH and CO. Adsorbed methanol may undergo further steam reforming by oxidative dehydrogenation to formate species, which decarbonylates via reverse decomposition to CO and H2O. Temperature programmed desorption/reaction and activity data confirmed that alkali promotion, especially at 1.8 %Na and higher loading, facilitates the forward acetate decomposition step, favoring decarboxylation over decarbonylation.
- Alhraki, Nour,Castro, Jonathan D.,Cronauer, Donald C.,Jacobs, Gary,Kropf, A. Jeremy,Martinelli, Michela,Matamoros, Maria E.
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- Light-Promoted Transfer of an Iridium Hydride in Alkyl Ether Cleavage
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A catalytic, light-promoted hydrosilylative cleavage reaction of alkyl ethers is reported. Initial studies are consistent with a mechanism involving heterolytic silane activation followed by delivery of a photohydride equivalent to a silyloxonium ion generated in situ. The catalyst resting state is a mixture of Cp*Ir(ppy)H (ppy = 2-phenylpyridine-κC,N) and a related hydride-bridged dimer. Trends in selectivity in substrate reduction are consistent with nonradical mechanisms for C-O bond scission. Irradiation of Cp*Ir(ppy)H with blue light is found to increase the rate of hydride delivery to an oxonium ion in a stoichiometric test. A comparable rate enhancement is found in carbonyl hydrosilylation catalysis, which operates through a related mechanism also involving Cp*Ir(ppy)H as the resting state.
- Fast, Caleb D.,Schley, Nathan D.
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supporting information
p. 3291 - 3297
(2021/10/12)
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- Dual Active Sites on Molybdenum/ZSM-5 Catalyst for Methane Dehydroaromatization: Insights from Solid-State NMR Spectroscopy
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Methane dehydroaromatization (MDA) on Mo/ZSM-5 zeolite catalyst is promising for direct transformation of natural gas. Understanding the nature of active sites on Mo/ZSM-5 is a challenge for applications. Herein, using 1H{95Mo} double-resonance solid-state NMR spectroscopy, we identify proximate dual active sites on Mo/ZSM-5 catalyst by direct observation of internuclear spatial interaction between Br?nsted acid site and Mo species in zeolite channels. The acidic proton–Mo spatial interaction is correlated with methane conversion and aromatics formation in the MDA process, an important factor in determining the catalyst activity and lifetime. The evolution of olefins and aromatics in Mo/ZSM-5 channels is monitored by detecting their host–guest interactions with both active Mo sites and Br?nsted acid sites via 1H{95Mo} double-resonance and two-dimensional 1H–1H correlation NMR spectroscopy, revealing the intermediate role of olefins in hydrocarbon pool process during the MDA reaction.
- Gao, Wei,Qi, Guodong,Wang, Qiang,Wang, Weiyu,Li, Shenhui,Hung, Ivan,Gan, Zhehong,Xu, Jun,Deng, Feng
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supporting information
p. 10709 - 10715
(2021/04/09)
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- Nonoxidative Methane Conversion on Granulated Mo/ZSM-5 Catalysts
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Abstract: Nonoxidative conversion of methane to aromatic hydrocarbons on granulatedМо/ZSM-5 catalysts was studied. The catalysts prepared using zeolites with thehierarchic pore system surpass in activity the catalysts prepared by thetraditional method, mi
- Stepanov,Kuvatova,Korobitsyna,Travkina,Vosmerikov,Kutepov
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p. 370 - 377
(2021/02/16)
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- Enhanced Cuprophilic Interactions in Crystalline Catalysts Facilitate the Highly Selective Electroreduction of CO2to CH4
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Cu(I)-based catalysts have proven to play an important role in the formation of specific hydrocarbon products from electrochemical carbon dioxide reduction reaction (CO2RR). However, it is difficult to understand the effect of intrinsic cuprophilic interactions inside the Cu(I) catalysts on the electrocatalytic mechanism and performance. Herein, two stable copper(I)-based coordination polymer (NNU-32 and NNU-33(S)) catalysts are synthesized and integrated into a CO2 flow cell electrolyzer, which exhibited very high selectivity for electrocatalytic CO2-to-CH4 conversion due to clearly inherent intramolecular cuprophilic interactions. Substitution of hydroxyl radicals for sulfate radicals during the electrocatalytic process results in an in situ dynamic crystal structure transition from NNU-33(S) to NNU-33(H), which further strengthens the cuprophilic interactions inside the catalyst structure. Consequently, NNU-33(H) with enhanced cuprophilic interactions shows an outstanding product (CH4) selectivity of 82% at -0.9 V (vs reversible hydrogen electrode, j = 391 mA cm-2), which represents the best crystalline catalyst for electrocatalytic CO2-to-CH4 conversion to date. Moreover, the detailed DFT calculations also prove that the cuprophilic interactions can effectively facilitate the electroreduction of CO2 to CH4 by decreasing the Gibbs free energy change of potential determining step (*H2COOH → *OCH2). Significantly, this work first explored the effect of intrinsic cuprophilic interactions of Cu(I)-based catalysts on the electrocatalytic performance of CO2RR and provides an important case study for designing more stable and efficient crystalline catalysts to reduce CO2 to high-value carbon products.
- Zhang, Lei,Li, Xiao-Xin,Lang, Zhong-Ling,Liu, Yang,Liu, Jiang,Yuan, Lin,Lu, Wan-Yue,Xia, Yuan-Sheng,Dong, Long-Zhang,Yuan, Da-Qiang,Lan, Ya-Qian
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supporting information
p. 3808 - 3816
(2021/04/07)
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- Integrated Capture and Conversion of CO2 to Methane Using a Water-lean, Post-Combustion CO2 Capture Solvent
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Integrated carbon capture and conversion of CO2 into materials (IC3M) is an attractive solution to meet global energy demand, reduce our dependence on fossil fuels, and lower CO2 emissions. Herein, using a water-lean post-combustion capture solvent, [N-(2-ethoxyethyl)-3-morpholinopropan-1-amine] (2-EEMPA), >90 % conversion of captured CO2 to hydrocarbons, mostly methane, is achieved in the presence of a heterogenous Ru catalyst under relatively mild reaction conditions (170 °C and 2 pressure). The catalytic performance was better in 2-EEMPA than in aqueous 5 m monoethanol amine (MEA). Operando nuclear magnetic resonance (NMR) study showed in situ formation of N-formamide intermediate, which underwent further hydrogenation to form methane and other higher hydrocarbons. Technoeconomic analyses (TEA) showed that the proposed integrated process can potentially improve the thermal efficiency by 5 % and reduce the total capital investment and minimum synthetic natural gas (SNG) selling price by 32 % and 12 %, respectively, compared to the conventional Sabatier process, highlighting the energetic and economic benefits of integrated capture and conversion. Methane derived from CO2 and renewable H2 sources is an attractive fuel, and it has great potential as a renewable hydrogen carrier as an environmentally responsible carbon capture and utilization approach.
- Burton, Sarah D.,Dagle, Robert A.,Heldebrant, David J.,Jiang, Yuan,Kothandaraman, Jotheeswari,Saavedra Lopez, Johnny,Walter, Eric D.
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p. 4812 - 4819
(2021/10/07)
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- Machine-Learning-Guided Discovery and Optimization of Additives in Preparing Cu Catalysts for CO2Reduction
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Discovery and optimization of new catalysts can be potentially accelerated by efficient data analysis using machine-learning (ML). In this paper, we record the process of searching for additives in the electrochemical deposition of Cu catalysts for CO2 reduction (CO2RR) using ML, which includes three iterative cycles: "experimental test; ML analysis; prediction and redesign". Cu catalysts are known for CO2RR to obtain a range of products including C1 (CO, HCOOH, CH4, CH3OH) and C2+ (C2H4, C2H6, C2H5OH, C3H7OH). Subtle changes in morphology and surface structure of the catalysts caused by additives in catalyst preparation can lead to dramatic shifts in CO2RR selectivity. After several ML cycles, we obtained catalysts selective for CO, HCOOH, and C2+ products. This catalyst discovery process highlights the potential of ML to accelerate material development by efficiently extracting information from a limited number of experimental data.
- Guo, Ying,He, Xinru,Su, Yuming,Dai, Yiheng,Xie, Mingcan,Yang, Shuangli,Chen, Jiawei,Wang, Kun,Zhou, Da,Wang, Cheng
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supporting information
p. 5755 - 5762
(2021/05/07)
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- The effect of supports on hydrogenation and water-tolerance of copper-based catalysts
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The effect of supports (SiO2, ZnO, ZrO2 and Al2O3) on the hydrogenation and water-tolerance of copper catalysts were studied at reaction condition containing water. The copper catalysts with different supports showed different hydrogenation and water-tolerance performances. The result of XRD, BET, Raman, TPR, XPS, N2O titration and TEM confirmed the interactions between copper and supports, and the formation of Cu-MxOy (M = Zn, Zr, and Al) interfaces had great effects on the catalytic activity and water-tolerance performance. In particular, too strong interactions suppressed the reduction of copper oxides, resulting in a low catalytic activity. Nevertheless, the formation of Cu-MxOy could provide more active sites, which provided more chances for the reactants to touch the active sites. By this method, the loss of active sites due to competitive adsorption between water and ethyl acetate could be made up, so that the water-tolerance of copper catalysts was improved.
- Chen, Zheng,Zhao, Xueying,Wei, Shuwei,Wang, Dengfeng,Zhang, Xuelan
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supporting information
p. 9967 - 9974
(2021/06/15)
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- Synthesis and reactivity of iridium complexes of a macrocyclic PNP pincer ligand
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Having recently reported on the synthesis and rhodium complexes of the novel macrocyclic pincer ligand PNP-14, which is derived from lutidine and features terminal phosphine donors trans-substituted with a tetradecamethylene linker (Dalton Trans., 2020, 49, 2077-2086 and Dalton Trans., 2020, 49, 16649-16652), we herein describe our findings critically examining the chemistry of iridium homologues. The five-coordinate iridium(i) and iridium(iii) complexes [Ir(PNP-14)(η2:η2-cyclooctadiene)][BArF4] and [Ir(PNP-14)(2,2′-biphenyl)][BArF4] are readily prepared and shown to be effective precursors for the generation of iridium(iii) dihydride dihydrogen, iridium(i) bis(ethylene), and iridium(i) carbonyl derivatives that highlight important periodic trends by comparison to rhodium counterparts. Reaction of [Ir(PNP-14)H2(H2)][BArF4] with 3,3-dimethylbutene induced triple C-H bond activation of the methylene chain, yielding an iridium(iii) allyl hydride derivative [Ir(PNP-14?)H][BArF4], whilst catalytic homocoupling of 3,3-dimethylbutyne into Z-tBuCCCHCHtBu could be promoted at RT by [Ir(PNP-14)(η2:η2-cyclooctadiene)][BArF4] (TOFinitial = 28 h-1). The mechanism of the latter is proposed to involve formation and direct reaction of a vinylidene derivative with HCCtBu outside of the macrocyclic ring and this suggestion is supported experimentally by isolation and crystallographic characterisation of a catalyst deactivation product. This journal is
- Hood, Thomas M.,Chaplin, Adrian B.
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p. 2472 - 2482
(2021/03/03)
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- Chromium-Based Catalysts and Processes for Converting Alkanes into Higher and Lower Aliphatic Hydrocarbons
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Processes for cracking an alkane reactant to form a lower aliphatic hydrocarbon product and for converting an alkane reactant into a higher aliphatic hydrocarbon product are disclosed, and these processes include a step of contacting the alkane reactant with a supported chromium (II) catalyst. In addition to the formation of various aliphatic hydrocarbons, such as linear alkanes, branched alkanes, 1-alkenes, and internal alkenes, aromatic hydrocarbons and hydrogen also can be produced.
- -
-
Paragraph 0081; 0082; 0086; 0104
(2021/03/19)
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- Properties and Reactivities of Zwitterionic Platinum(II)-ate Complexes Generated by Transforming Coordination of an Alkyne-Bisphosphine Ligand
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Coordination of an alkyne-bisphosphine ligand with platinum(II) precursors produced a structural reorganization in the ligand backbone to form stable zwitterionic platinum(II) complexes bearing an anionic platinum center. The structural properties and reactivities of these complexes were investigated using X-ray crystallographic analyses, computational studies, and stoichiometric reactions involving oxidative addition and reductive elimination. These studies have shown that the enhanced nucleophilicity of the platinum center to alkyl halides promotes smooth oxidative addition and that the charge rebalance accelerates the dissociation of the halide anion from the platinum(IV) intermediate, which is essential in the carbon-carbon bond-forming step.
- Okamoto, Kazuhiro,Sasakura, Kohei,Funasaka, Satoshi,Watanabe, Hiiro,Suezaki, Masahiro,Ohe, Kouichi
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supporting information
p. 848 - 856
(2021/05/04)
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- Redox Activity of Pyridine-Oxazoline Ligands in the Stabilization of Low-Valent Organonickel Radical Complexes
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Low-valent organonickel radical complexes are common intermediates in cross-coupling reactions and metalloenzyme-mediated processes. The electronic structures of N-ligand supported nickel complexes appear to vary depending on the actor ligands and the coordination number. The reduction products of a series of divalent (pyrox)Ni complexes establish the redox activity of pyrox in stabilizing electron-rich Ni(II)-alkyl and -aryl complexes by adopting a ligand-centered radical configuration. The reduced pyrox imparts an enhanced trans-influence. In contrast, such redox activity was not observed in a (pyrox)Ni(I)-bromide species. The excellent capability of pyrox in stabilizing electron-rich Ni species resonates with its proclivity in promoting the reductive activation of C(sp3) electrophiles in cross-coupling reactions.
- Wagner, Clifton L.,Herrera, Gabriel,Lin, Qiao,Hu, Chunhua T.,Diao, Tianning
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supporting information
p. 5295 - 5300
(2021/05/04)
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- Tuning supported Ni catalysts by varying zeolite Beta heteroatom composition: effects on ethylene adsorption and dimerization catalysis
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The influence of zeolite heteroatom composition on the electron density and catalytic activity of a supported Ni cation is examined. Ni-[X]-Beta catalysts, where X = Al, Ga, Fe, or dealuminated, were synthesized and characterized with probe molecule adsorption with FTIR spectroscopy and C2H4dimerization catalysis. It was observedviaCO adsorption that supported Ni cations were increasing in electron density in the order: [Fe] > [Ga] > [Al]. C2H4dimerization activity increased with increasing electron density of the Ni cation. Despite similarities in reported acid site strength, the acid sites on [Fe]-Beta in this work had significantly lower activity than those on [Ga]-Beta for the skeletal isomerization of linear butenes as well as C2H4dimerization. Introducing H2as a reactant resulted in a decrease in dimerization activity for Ni-[Al]-Beta and Ni-[Ga]-Beta but an increase for Ni-[Fe]-Beta. The selectivity and activity of Ni-[DeAl]-Beta changed dramatically with the introduction of H2, which subsequently converted all C2H4withca.100% selectivity towards C2H6(even with a lower space velocity relative to without H2). These results demonstrate the ability of heteroatom composition to tune catalysis by using C2H4dimerization catalysis as a test reaction with zeolite Beta supported Ni catalysts.
- Meloni, Michael,Runnebaum, Ron C.
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p. 3393 - 3401
(2021/06/06)
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- Preparation of a hollow HZSM-5 zeolite supported molybdenum catalyst by desilication-recrystallization for enhanced catalytic properties in propane aromatization
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A hollow HZSM-5 supported molybdenum (Mo) catalyst was successfully prepared by desilication-recrystallization method of HZSM-5 in tetrapropylammonium hydroxide (TPAOH) solution. The as-synthesized catalyst exhibiting excellent performance in propane aromatization reaction was thoroughly investigated, along with the mechanism for the formation of hollow structure and mechanism for the deactivation. Results revealed that TPA ?+ ?exerted a controllable desilication and recrystallization effect. Compared with Na2CO3 treatment which led to a mesoporous structure, TPAOH treatment was able to leach out the inner Si species by OH- and then those Si species recrystallized on the external surface, resulting in the hollow structure and a silicon-rich external surface. In addition, the hollow zeolite exposing higher external surface provided more anchoring sites for Mo species, which was beneficial to the Mo related Lewis acid sites but decreased the surface Bronsted acidity. At 823 ?K and a space velocity of 1800 ?mL·g-1·h-1, the hollow Mo/HZSM-5(TPAOH) catalyst behaved a propane conversion of 73.01% and aromatics selectivity of 77.36%, exceeding those of the hierarchical Mo/HZSM-5(Na2CO3) catalyst by 5.97% and 9.96%, respectively. These features of Mo/HZSM-5(TPAOH) granted it superb diffusion ability and optimized Bronsted/Lewis acid ratio (B/L ?= ?1.3), which greatly enhanced the propane conversion and aromatic selectivity together with a preeminent catalytic stability.
- Cheng, Junjun,Wei, Ting,Xu, Guohao,Yang, Fan,Zhang, Peng,Zhu, Xuedong
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- Fischer-Tropsch to olefins over Co2C-based catalysts: Effect of thermal pretreatment of SiO2 support
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SiO2 supported Co2C-based catalysts were used for Fischer-Tropsch to olefins (FTO), and the effect of thermal pretreatment of SiO2 support under different temperatures on the Co2C morphology and catalytic performance was investigated. It was found that the interaction between cobalt and support was weakened when SiO2 was pretreated at high temperature (990 °C) due to the decreased content of surface Si[sbnd]OH groups. The relative weak interaction between cobalt and support benefited the formation of cobalt manganese composite oxide after calcination and reduction, and thus promoted the generation of Co2C nanoprisms with promising FTO performance. In contrast, for the SiO2 support pretreated at 350 °C or 650 °C, the strong interaction between cobalt and support led to phase separation of cobalt and manganese. As a result, only Co2C nanospheres were generated which displayed low activity and high methane selectivity.
- An, Yunlei,Li, Liusha,Li, Xiao,Lin, Tiejun,Sun, Yuhan,Yu, Fei,Zhong, Liangshu
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- Oxidative coupling of methane over sodium zirconate catalyst
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We report the oxidative coupling of methane (OCM) performance over Na2ZrO3under various temperatures, CH4/O2ratios, and reaction pressures. Sensitivity of CH4conversion rate was investigated with resp
- Lundin, Sean-Thomas B.,Siritanaratkul, Bhavin,Takanabe, Kazuhiro
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p. 4803 - 4811
(2021/07/26)
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- Reactors for Preparing Valuable Hydrocarbons and Hydrogen From Methane Through Non-Oxidative Pyrolysis
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According to this disclosure, there is provided a pyrolysis reaction system and a direct non-oxidative methane coupling process using the same by which it is possible to reach the selectivity for good C≤10 hydrocarbons and at the same time to inhibit coke from being generated while a good methane conversion is maintained during direct conversion of methane into C2+ hydrocarbons through non-oxidative pyrolysis.
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Paragraph 0084-0091; 0099
(2021/10/11)
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- Direct Evidence on the Mechanism of Methane Conversion under Non-oxidative Conditions over Iron-modified Silica: The Role of Propargyl Radicals Unveiled
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Radical-mediated gas-phase reactions play an important role in the conversion of methane under non-oxidative conditions into olefins and aromatics over iron-modified silica catalysts. Herein, we use operando photoelectron photoion coincidence spectroscopy to disentangle the elusive C2+ radical intermediates participating in the complex gas-phase reaction network. Our experiments pinpoint different C2-C5 radical species that allow for a stepwise growth of the hydrocarbon chains. Propargyl radicals (H2C?C≡C?H) are identified as essential precursors for the formation of aromatics, which then contribute to the formation of heavier hydrocarbon products via hydrogen abstraction–acetylene addition routes (HACA mechanism). These results provide comprehensive mechanistic insights that are relevant for the development of methane valorization processes.
- ?ot, Petr,Hemberger, Patrick,Pan, Zeyou,Paunovi?, Vladimir,Puente-Urbina, Allen,van Bokhoven, Jeroen Anton
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supporting information
p. 24002 - 24007
(2021/10/01)
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- New aspects of parahydrogen-induced polarization for C2—C3 hydrocarbons using metal complexes
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The parahydrogen-induced polarization technique allows one to significantly enhance the NMR signal. Novel results on the parahydrogen-induced polarization of C2—C3 hydrocarbons using metal complexes are presented. Gaseous propane with the nuclear spin polarization level of at least 0.8% can be produced by bubbling parahydrogen through a solution of propylene and a homogeneous hydrogenation catalyst. Hydrogenation of acetylene with parahydrogen over Wilkinson’s catalyst can result in the formation of hyperpolarized ethylene. The shape of the NMR lines indicates that this reaction proceeds as a syn-addition of molecular hydrogen. The reactions of several ethylene complexes of rhodium and platinum with parahydrogen were studied. The [Rh(η2-C2H4)2Cl]2 complex reacts with parahydrogen to form hyperpolarized ethane, whereas [Pt(η2-C2H4)(PPh3)2] converts to the hyperpolarized dihydride complex cis-[Pt(H)2(PPh3)2].
- Burueva, D. B.,Chekmenev, E. Y.,Goodson, B. M.,Koptyug, I. V.,Kovtunov, K. V.,Salnikov, O. G.,Sviyazov, S. V.
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p. 2382 - 2389
(2022/01/31)
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- Selective Oxidative Cracking of n-Butane to Light Olefins over Hexagonal Boron Nitride with Limited Formation of COx
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In recent years, hexagonal boron nitride (hBN) has emerged as an unexpected catalyst for the oxidative dehydrogenation of alkanes. Here, the versatility of hBN was extended to alkane oxidative cracking chemistry by investigating the production of ethylene and propylene from n-butane. Cracking selectivity was primarily controlled by the ratio of n-butane to O2 within the reactant feed. Under O2-lean conditions, increasing temperature led to increased selectivity to ethylene and propylene and decreased selectivity to COx. In addition to surface-mediated chemistry, homogeneous gas-phase reactions likely contributed to the observed product distribution, and a reaction mechanism was proposed based on these observations. The catalyst showed good stability under oxidative cracking conditions for 100 h time-on-stream while maintaining high selectivity to ethylene and propylene.
- McDermott, William P.,Venegas, Juan,Hermans, Ive
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p. 152 - 158
(2019/11/13)
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- Oxidative Methane Conversion to Ethane on Highly Oxidized Pd/CeO2 Catalysts Below 400 °C
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Methane upgrading into more valuable chemicals has received much attention. Herein, we report oxidative methane conversion to ethane using gaseous O2 at low temperatures (cat ?1 h?1. The Pd?O?Pd sites, not Pd?O?Ce, were the active sites for the selective ethane production at low temperatures. Density functional theory calculations confirmed that the Pd?O?Pd site is energetically more advantageous for C?C coupling, whereas Pd?O?Ce promotes CH4 dehydrogenation. The ceria helped Pd maintain a highly oxidic state despite reductive CH4 flow. This work can provide new insight for methane upgrading into C2 species.
- Kwon, Gihun,Shin, Dongjae,Jeong, Hojin,Sahoo, Suman Kalyan,Lee, Jaeha,Kim, Gunjoo,Choi, Juhyuk,Kim, Do Heui,Han, Jeong Woo,Lee, Hyunjoo
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p. 677 - 681
(2020/02/11)
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