Copper-supported catalysts in methanol synthesis and water gas shift reaction

The comparative studies of physicochemical properties of Cu-support catalysts (support = ZnO, Al₂O₃, Cr₂O₃, ZnAl₂O₄, FeAlO₃, or CrAl₃O₆) and their catalytic activity in methanol synthesis and water gas shift reaction were the main goal of this work. The promotion effect of copper addition in both reaction was proved. The formation of spinel type structure CuCr₂O₄, ZnAl₂O₄ and binary oxide CrAl₃O₆, FeAlO₃ during calcination process was confirmed by XRD technique. Results showed that 20% Cu/FeAlO₃ had the best performance in water gas shift reaction. The best selective and active catalyst in methanol synthesis was 20% Cu/ZnAl₂O₄.     

Catalytic activity of aluminium-rich hematite in the water gas shift reaction

Aluminium-rich hematite was found to catalyze the water gas shift reaction but there is a compromise between the increase in specific surface area and the intrinsic activity. This revised version was published online in June 2006 with corrections to the Cover Date.     

Ferrofluid catalyzed water gas shift reaction to give carbon-dioxide and hydrogen

A ferrofluid consisting of colloidally dispersed magnetite particles in water was found to be an efficient selective catalyst for water gas shift reaction at 15–25 atmosphere of CO pressure in the temperature range of 423–553 K where the products obtained were only CO₂ and H₂. The reaction was studied as a function of variation of the concentration of catalyst, pressure of CO gas and temperature. Kinetic parameters suggested a mechanism involving first order dependence in CO and catalyst concentrations.     

On the mechanism of low-temperature water gas shift reaction on copper

Periodic, self-consistent density functional theory (DFT-GGA) calculations are used to investigate the water gas shift reaction (WGSR) mechanism on Cu(111). The thermochemistry and activation energy barriers for all the elementary steps of the commonly accepted redox mechanism, involving complete water activation to atomic oxygen, are presented. Through our calculations, we identify carboxyl, a new reactive intermediate, which plays a central role in WGSR on Cu(111). The thermochemistry and activation energy barriers of the elementary steps of a new reaction path, involving carboxyl, are studied. A detailed DFT-based microkinetic model of experimental reaction rates, accounting for both the previous and the new WGSR mechanism show that, under relevant experimental conditions, (1) the carboxyl-mediated route is the dominant path, and (2) the initial hydrogen abstraction from water is the rate-limiting step. Formate is a stable "spectator" species, formed predominantly through CO2 hydrogenation. In addition, the microkinetic model allows for predictions of (i) surface coverage of intermediates, (ii) WGSR apparent activation energy, and (iii) reaction orders with respect to CO, H2O, CO2, and H2.     

Catalytic properties of copper chromite ferrites in water gas shift reaction and hydrogen oxidation

The catalytic properties of a series of copper chromite ferrite samples with the composition CuCr_2–xFe_xO₄ (where x = 0–2) and a spinel-type structure in reactions with reducing (water gas shift reaction, WGSR) and oxidizing (the oxidation of hydrogen) reaction atmospheres were studied. The samples were obtained by the thermal decomposition of mixed hydroxo compounds. The distribution of Cu²⁺ ions in the tetrahedral and octahedral crystallographic positions of spinel, which depends on the Cr³⁺/Fe³⁺ ratio, affects the apparent activation energy (E_a) in both of the reactions. In WGSR, E_a is ～33 kJ/mol for CuCr₂O₄, in which Cu²⁺ ions mainly occupy tetrahedral positions, whereas E_a ≈ 100 kJ/mol for CuFe₂O₄, in which Cu²⁺ ions mainly occupy octahedral positions. In the reaction of hydrogen oxidation, E_a is ～71 kJ/mol for CuCr₂O₄ or ～42 kJ/mol for CuFe₂O₄. The value of E_a for the mixed chromite ferrites changes with the replacement of chromium ions by iron ions and, hence, with a ratio between the amounts of copper ions in the tetrahedral and octahedral oxygen positions of spinel.     

A theoretical study of metal-metal cooperativity in the homogeneous water gas shift reaction

The possibility of metal-metal cooperativity in improving the yield of the homogeneous water gas shift reaction (WGSR) has been investigated through full quantum mechanical density functional theory calculations. The calculations indicate that bimetallic catalysts would be likely to be more highly active than mononuclear metal-based catalysts for the WGSR. The results have implications for the design of improved WGSR catalysts in the future.     

MoO_x促进的Pt基催化剂用于低温水汽变换反应(英文)

通过浸渍还原法制备了不同比例的Pt-Mo/SiO_2催化剂,采用X射线衍射、透射电镜、X射线近边吸收谱和X射线光电子能谱表征了Pt-Mo/SiO_2催化剂的组成、结构及价态.研究结果表明,少量MoO_x修饰Pt-Mo/SiO_2催化剂在低温水汽变换反应中表现出比Pt/SiO_2催化剂更高的催化活性,过量MoO_x包覆的Pt-Mo/SiO_2催化剂活性较低.低温水汽变换反应活性来自于Pt与表面MoO_x的界面协同作用,限域在Pt纳米颗粒表面的MoO_x表现出较低价态,高分散MoO_x纳米岛修饰的Pt纳米颗粒是低温水汽变换反应的活性结构.     

Homogeneous catalysis of the water gas shift reaction by iridium carbonyl in alkaline solution

The water gas shift reaction, H₂O + CO ? H₂ + CO₂, catalyzed homogeneously by a system based on tetrairidiumdodecacarbonyl (Ir₄(CO)₁₂) in alkaline 2-ethoxyethanol/water solution was examined at moderate temperatures (90–130°C) and pressures (P_CO 0.5–2.0 atm). The catalytic reaction showed an approximate first-order dependence on base concentration and on the concentration of iridium. The catalytic cycle was shown to have a zero order dependence on the partial pressure of CO. An apparent activation energy of 10.7 kcal mol^?1 was obtained from a linear Arrhenius plot based on hydrogen production over the temperature range 90–130°C. The predominant pathway of the reaction can be explained by a mechanism in which activation of CO by nucleophilic attack of hydroxide on the metal hydride species HIr₄(CO)₁₁^? produces the dihydride species, H₂Ir₄(CO)₁₀^2? in the rate-limiting step. Subsequent reaction of this anion with H₂O gives H₂ plus HIr₄(CO)₁₁^? again. The complex Ir₈(CO)₂₀^2? is shown to be a catalytically poor component of the solution. The system has also been shown to be active toward the decomposition of formate. This pathway however, is concluded to make an insignificant contribution to the catalysis rate under water gas shift reaction conditions.     

Cu-Pt-Au三元合金催化水煤气变换反应的密度泛函研究

利用密度泛函理论（DFT）研究了不同掺杂量的Cu-Pt-Au催化剂性质及水煤气变换反应（WGSR）在催化剂表面上的反应机理。首先对Cu-Au和Pt-Au二元催化剂的稳定性和电子活性进行研究,发现Pt-Au催化剂的协同效应较优,稳定性更优,结合能为77.15 eV,d带中心为-3.18 eV。当将Cu继续掺杂到Pt-Au合金中构成Cu-Pt-Au三元催化剂时,Cu₃-Pt₃-Au（111）结合能为77.99 eV,且d带中心为-3.05 eV,表明其具有较优的稳定性和电子活性。探讨了WGSR在Cu₃-Pt₃-Au（111）上的反应历程,氧化还原机理因CO氧化的能垒达到4.84 eV而不易进行。CHO和COOH两个中间体为竞争关系,且形成CHO中间物时的能垒较小,因此,反应相对容易按照甲酸机理进行。     

Metal doped silica membrane reactor: Operational effects of reaction and permeation for the water gas shift reaction

In this work, we investigate the performance of metal (Cobalt) doped silica membranes in a membrane reactor (MR) configuration for the low temperature water gas shift (WGS) reaction. The membranes were hydrostable and showed activated transport even after 2 weeks exposure to steam. High CO conversions resulted in the H₂ and CO partial pressures in the reaction chamber moving in opposite directions, thus favouring H₂/CO separation to treble (5–15) from 150 to 250 °C. On the other hand, the separation of H₂/CO₂ remained relatively low (2–4) as the driving force for diffusion or partial pressure of these gases remained equal in the reaction chamber irrespective of the extent of conversion. Below approximately 40% CO conversion, the MR is ineffective as the H₂ driving force for permeation was so low that H₂/CO selectivity was below unity. Operating under equilibrium limited conversion (space velocities 7500 h⁻¹) conditions, very high conversions in excess of 95% were observed and there were no significant advantages of the MR performance over the packed bed reactor (PBR). However, for higher throughputs (space velocities 38000 and 75000 h⁻¹) conversion is affected by the reaction rate, and relatively enough H₂ is removed from the reactor through the membrane. Increasing temperature to 250 °C as a function of the space velocity (75000 h⁻¹) allowed for the CO conversion in the MR to shift up to 12% as compared to the PBR.     

NiCe bimetallic nanoparticles embedded in hexagonal mesoporous silica (HMS) for reverse water gas shift reaction

Reverse water gas shift (RWGS) reaction is a crucial process in CO₂ utilization. Herein, Ni- and NiCe-containing hexagonal mesoporous silica (Ni-HMS and NiCe-HMS) catalysts were synthesized using an in-situ one-pot method and applied for RWGS reaction. At certain reaction temperatures 500-750 °C, Ni-HMS samples displayed a higher selectivity to the preferable CO than that of conventionally impregnated Ni/HMS catalyst. This could be originated from the smaller NiO nanoparticles over Ni-HMS catalyst. NiCe-HMS exhibited higher activity compared to Ni-HMS. The catalysts were characterized by means of TEM, XPS, XRD, H₂-TPR, CO₂-TPD, EPR and N₂ adsorption-desortion technology. It was found that introduction of Ce created high concentration of oxygen vacancies, served as the active site for activating CO₂. Also, this work analyzed the effect of the H₂/CO₂ molar ratio on the best NiCe-HMS. When reaction gas H₂/CO₂ molar ratio was 4 significantly decreased the selectivity to CO at low temperature, but triggered a higher CO₂ conversion which is close to the equilibrium.     

CeO_2-Al_2O_3负载金催化剂用于水煤气变换反应的催化活性

采用浸渍法和沉积-沉淀法制备了CeO2-Al2O3复合氧化物,比较了复合氧化物负载纳米金催化剂对水煤气变换反应的催化活性。通过N2物理吸附、XRD、TEM、H2-TPR等表征手段对复合氧化物及其负载金催化剂的物相和结构进行分析,发现复合氧化物的制备方法及其焙烧温度对其比表面积、孔结构及水煤气变换反应活性有明显的影响。与沉积-沉淀法相比,浸渍法制备的CeO2-Al2O3复合氧化物具有较大的CeO2晶粒尺寸,经500℃焙烧后再负载金,所得催化剂具有更高的活性,250℃时CO转化率可达78.1%。     

Effect of copper oxide on the catalytic activity of iron-chromia catalyst for water gas shift reaction

It has been established that copper oxide promotes the catalytic activity of iron-chromia catalyst in the water gas shift reaction due to the formation of catalytically active aggregates. However, due to their gradual recrystallization and sintering into larger copper particles, the promoting effect sharply decreases.

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Low-temperature water gas shift reaction on Cu/SiO2 prepared by an atomic layer epitaxy technique

An atomic layer epitaxy technique was used to produce nanoscale 2.9-3.4 nm copper particles supported on silica, and the nanoscale Cu/SiO2 catalysts can show surprisingly high activity for the water gas shift reaction, in comparison with the 5.6 wt% Pt/SiO2 and 10.3 wt% Cu/SiO2 prepared by the impregnation method.     

New approaches to the preparation of highly efficient chromium-containing oxide catalysts for the water gas shift reaction

It was found experimentally that the solutions of Cr³⁺ nitrate and the nitrates of other metals that are the constituents of Cr-containing catalysts can be prepared by dissolving a corresponding metal (for example, cast iron and electrolytic copper) in a solution of chromic anhydride and nitric acid to reach the quantitative reduction of Cr⁶⁺ without the formation of nitrogen oxides. Analogously, the oxidation of Fe²⁺ cations to Fe³⁺ coupled with the reduction of hexavalent chromium can be performed. The precipitation of Fe³⁺, Cr³⁺, and Cu²⁺ ions at a ratio of Fe: Cr = 9 and a concentration of Cu²⁺ to 20 at % can result in the formation of a partially hydrated oxide with the hydrohematite structure—a dispersed and highly defective oxide structure with a high specific surface area more than 300 m²/g and a higher thermal stability, as compared with the goethite phase (α-FeOOH). The dehydration of hydrohematite occurred at a noticeable rate at temperatures higher than 400°C. Hydrohematite promoted with copper cations exhibited high activity below 400°C; this can decrease the starting temperature of the adiabatic high-temperature WGSR to 300°C or below.     

不同金属催化水煤气变换反应活性的Monte Carlo模拟研究

运用BOC-MP方法对Cu(110),Cu(111),Pd(111)和Au(111)等过渡金属催化的WGS反应的可能微观动力学步骤进行了详尽的能学数据计算,并结合MonteCarlo方法对WGS反应的表面氧化还原机理进行了计算机模拟。结果表明,Cu的催化活性优于Pd,Au的催化活性,并获得了相应金属上WGS反应的表观活化能及动力学指前因子(相对值);在此基础上,对该反应的结构敏感性进行了研究,发现该反应为一结构敏感反应,与实验结果相符。     

Activity promotion of anti-sintering AuMgGa2O4 using ceria in the water gas shift reaction and catalytic combustion reactions

Heterogeneous gold nanocatalysts have both inspired researchers with their unique catalytic performance and frustrated them due to the contradictions observed in their activities and stabilities. A recent breakthrough has shown that gold nanoparticles (NPs) can retain their catalytically active size over a MgGa₂O₄ spinel support upon sintering at high temperatures. Herein, we report the catalytic activity of anti-sintering Au

MgGa₂O₄ for use in water gas shift reaction (WGSR) and catalytic combustion reactions, and the promoting effect of ceria. Upon adding ceria to 800°C-aged Au

MgGa₂O₄, the CO conversion in the WGSR was increased from ～1.5% to ～34.0% at 450°C, and the “light-off” temperatures (T₅₀) for methane combustion and CO oxidation were decreased by ～80 and ～100°C, respectively. Characterizations using XRD, HAADF-STEM, EDS mapping, H₂-TPR, XPS, and DRIFTs confirmed the proximate contact of Au with ceria and their significant synergistic effect, which thereby combined the benefits of ceria toward the dissociation of H₂O or O₂ and the Au NPs toward activating CO or CH₄. These results show that this stepwise stabilization-activation strategy is efficient for rationally constructing stable and active gold nanocatalysts, which may open up possibilities for the wide application of gold nanocatalysts at elevated temperatures.     

High activity carbide supported catalysts for water gas shift

Nanostructured carbides are refractory materials with high surface areas that could be used as alternatives to the oxide materials that are widely used as support materials for heterogeneous catalysts. Carbides are also catalytically active for a variety of reactions, offering additional opportunities to tune the overall performance of the catalyst. In this paper we describe the synthesis of molybdenum carbide supported platinum (Pt/Mo(2)C) catalysts and their rates for the water gas shift reaction. The synthesis method allowed interaction of the metal precursor with the native, unpassivated support. The resulting materials possessed very high WGS rates and atypical Pt particle morphologies. Under differential conditions, rates for these catalysts were higher than those for the most active oxide-supported Pt catalysts and a commercial Cu-Zn-Al catalyst. Experimental and computational results suggested that active sites on the Pt/Mo(2)C catalysts were located on the perimeter of the Pt particles and that strong interactions between Pt and the Mo(2)C surface gave rise to raft-like particles.     

沉淀剂对铜锰复合氧化物变换催化剂构效的影响

以CuSO4.5H2O和MnSO4.H2O为原料,KOH和NaOH为沉淀剂制备了铜锰复合氧化物,考察了其变换反应催化性能,利用XRD、低温氮气吸附法、TG、H2-TPR等对所合成样品进行了表征。以KOH和NaOH为沉淀剂所得沉淀终产物的物相组成和织构明显不同,分别为层状结构碱式硫酸铜Cu4SO4(OH)6.H2O及无定形锰氧化物和Cu2+1O和Mn3O4混合物。两种物相组成和织构完全不同的沉淀终产物焙烧后都生成Cu1.5Mn1.5O4固熔体,在变换反应条件下均转化为Cu和MnO,但其催化性能却有明显差异。以NaOH为沉淀剂,得到以Cu2+1O和Mn3O4复合体为主的沉淀终产物,焙烧及还原后保持了较高的织构稳定性,提高了样品的活性和热稳定性。而以KOH为沉淀剂得到以层状结构碱式硫酸铜Cu4SO4(OH)6.H2O和无定形锰氧化物为主的沉淀终产物,在焙烧过程发生的演变极其复杂,削弱了铜锰组分协同效应,造成其活性和热稳定性极差。研究结果表明,NaOH作沉淀剂所制备样品的织构稳定性、催化活性显著高于以KOH作沉淀剂所制备样品,且热稳定性良好。     

CeO2-Al2O3负载金催化剂用于水煤气变换反应的催化活性

采用浸渍法和沉积 沉淀法制备了CeO₂-Al₂O₃复合氧化物,比较了复合氧化物负载纳米金催化剂对水煤气变换反应的催化活性。通过N2物理吸附、XRD、TEM、H₂-TPR等表征手段对复合氧化物及其负载金催化剂的物相和结构进行分析,发现复合氧化物的制备方法及其焙烧温度对其比表面积、孔结构及水煤气变换反应活性有明显的影响。与沉积 沉淀法相比,浸渍法制备的CeO₂-Al₂O₃复合氧化物具有较大的CeO₂晶粒尺寸,经500℃焙烧后再负载金,所得催化剂具有更高的活性,250℃时CO转化率可达78.1%。