Preparation and High-Temperature Water-Gas Shift Catalytic Features of La_(1-x)Ce_x FeO_3 Perovskite

Based on water-gas shift reaction mechanism and perovskite compounds characteristics, La_(1- x )Ce_ x FeO_3 (.K) perovskite were designed and prepared as shift catalysts. DTA and XRD results reveal that La_(1- x )Ce_ x FeO_3 can be formed at 730～760 ℃ by mechanic-mix thermal decomposition method. Activity and heat-resisting tests show that La_(1- x )Ce_ x FeO_3 ((.K)) possess high thermal stability if x is less than or equals to 0.5. But when x is greater than 0.5, La_(1- x )Ce_ x FeO_3 (.K) will be converted into ceria and magnetite partially or completely under shift reaction conditions. In the case of x =0.5, the conversion of CO is about 68% at 530 ℃. Potassium can greatly improve the low temperature activity, but slightly reduces the high temperature activity, and has little impact on the thermal stability. La_(0.5)Ce_(0.5)FeO_3 (.K) is a promising chromium-free high temperature shift catalyst.

Water gas shift activity of Co-Mo/MgO-Al_2O_3 catalysts presulfided with ammonium sulfide

Co-Mo/MgO-Al2O3 catalyst was presulfided with ammonium sulfide in aqueous solution and activated with synthesis gas for water gas shift reaction. The assay results indicate that the presulfided Co-Mo/MgO-Al2O3 catalyst exhibits an excellent catalytic activity and stability. XRD and EPR characterization results show that the O-S exchange might occur during the impregnation, leading to the formation of （NH4）2MoS4 （or （NH4）zMoxSy） precursor, which was then thermally decomposed and reduced to MoS2. The higher catalytic performance is attributed to an optimization formation of active Co-Mo sulfides, consisting of well dispersed MoS2 and Co-Mo-S phase due to the redispersion of Co sulfide particles over the edges of newly formed MoS2 crystallites.

Catalytic Reduction of CO2 to CO via Reverse Water Gas Shift Reaction:Recent Advances in the Design of Active and Selective Supported Metal Catalysts

The catalytic conversion of CO2 to CO via a reverse water gas shift(RWGS)reaction followed by well-established synthesis gas conversion technologies may provide a potential approach to convert CO2 to valuable chemicals and fuels.However,this reaction is mildly endothermic and competed by a strongly exothermic CO2 methanation reaction at low temperatures.Therefore,the improvement in the low-temperature activities and selectivity of the RWGS reaction is a key challenge for catalyst designs.We reviewed recent advances in the design strategies of supported metal catalysts for enhancing the activity of CO2 conversion and its selectivity to CO.These strategies include varying support,tuning metal–support interactions,adding reducible transition metal oxide promoters,forming bimetallic alloys,adding alkali metals,and enveloping metal particles.These advances suggest that enhancing CO2 adsorption and facilitating CO desorption are key factors to enhance CO2 conversion and CO selectivity.This short review may provide insights into future RWGS catalyst designs and optimization.

Effect of Addition Sequence during Neutralization and Precipitation on Iron-based Catalysts for High Temperature Shift Reaction

The preparation of the iron-based catalysts promoted by cobalt with a small amount of copper and aluminum for the high temperature shift reaction （HTS） with different sequences of adding catalyst raw materials during neutralization and precipitation was investigated. XRD, BET and particle size distribution （PSD） were used to characterize the prepared catalysts. It was found that the catalyst crystals were all γ-Fe2O3, and the intermediate of the catalyst after aging was Fe3O4. The crystallographic form of the catalyst and its intermediate was not affected by the addition sequence in the neutralization and precipitation process. The results showed that the specific surface area and the particle size of the catalysts depended on the addition sequence to the mother liquor. Cobalt with a small amount of copper and aluminum could increase the specific surface area and decrease the particle size of catalysts.

Effects of ZrO_2 Content on Structure and Performance of Cu/CeO_2-ZrO_2 Catalysts for Water-Gas Shift Reaction

Cu/CeO2-ZrO2 catalysts for water-gas shift （WGS） reaction were prepared with co-precipitation method, and the influence of ZrO2 content on the catalytic structure and properties was investigated by the techniques of N2 physical adsorption analysis, XRD and H2-TPR. The results indicate that the BET surface areas of the catalysts are increased in varying degrees due to the presence of ZrO2. With increasing ZrO2 content, the pore size distribution is centered on 1.9 nm. ZrO2 can efficiently restrain the growth of Cu crystal particles. The appropriate amount of ZrO2 in the Cu/CeO2 catalysts can help the catalyst keep better copper dispersion in the WGS reaction, which can lead to both higher catalytic activity and better thermal stability. When ZrO2 content is 10% （atom fraction）, Cu/CeO2-Zr02 catalyst reaches a CO conversion rate of 73.7% at the reaction temperature of 200℃.

Boosting the water gas shift reaction on Pt/CeO_(2)-based nanocatalysts by compositional modification: Support doping versus bimetallic alloying

The water gas shift reaction is of vital significance for the generation and transition of energy due to the application in hydrogen production and industries such as ammonia synthesis and fuel cells.The influence of support doping and bimetallic alloying on the catalytic performance of Pt/Ce O_(2)-based nanocatalysts in water gas shift reaction was reported in this work.Various lanthanide ions and 3d transition metals were respectively introduced into the Ce O_(2)support or Pt to form Pt/Ce O_(2):Ln(Ln=La,Nd,Gd,Tb,Yb)and Pt M/Ce O_(2)(M=Fe,Co,Ni)nanocatalysts.The sample of Pt/Ce O_(2):Tb showed the highest activity(TOF at 200℃=0.051 s^(-1))among the Pt/Ce O_(2):Ln and the undoped Pt/Ce O_(2)catalysts.Besides,the sample of Pt Fe/Ce O_(2)exhibited the highest activity(TOF at 200℃=0.12 s^(-1))among Pt M/Ce O_(2)catalysts.The results of the multiple characterizations indicated that the catalytic activity of Pt/Ce O_(2):Ln catalysts was closely correlated with the amount of oxygen vacancies in doped ceria support.However,the different activity of Pt M/Ce O_(2)bimetallic catalysts was owing to the various Pt oxidation states of the bimetals dispersed on ceria.The study of the reaction pathway indicated that both the samples of Pt/Ce O_(2)and Pt/Ce O_(2):Tb catalyzed the reaction through the formate pathway,and the enhanced activity of the latter derived from the increased concentration of oxygen vacancies along with promoted water dissociation.As for the sample of Pt Fe/Ce O_(2),its catalytic mechanism was the carboxyl route with a higher reaction rate due to the moderate valence of Pt along with improved CO activation.

Strong metal-support interactions between highly dispersed Cu^(+) species and ceria via mix-MOF pyrolysis toward promoted water-gas shift reaction

The modulation of metal-support interfacial interaction is significant but challenging in the design of high-efficiency and high-stability supported catalysts.Here,we report a synthetic strategy to upgrade Cu-CeO_(2)interfacial interaction by the pyrolysis of mixed metal-organic framework(MOF)structure.The obtained highly dispersed Cu/CeO_(2)-MOF catalyst via this strategy was used to catalyze water-gas shift reaction(WGSR),which exhibited high activity of 40.5μmolCOgcat^(-1).s^(-1)at 300℃and high stability of about 120 h.Based on comprehensive studies of electronic structure,pyrolysis strategy has significant effect on enhancing metal-support interaction and then stabilizing interfacial Cu^(+)species under reaction conditions.Abundant Cu^(+)species and generated oxygen vacancies over Cu/CeO_(2)-MOF catalyst played a key role in CO molecule activation and H2O molecule dissociation,respectively.Both collaborated closely and then promoted WGSR catalytic performance in comparison with traditio nal supported catalysts.This study shall offer a robust approach to harvest highly dispersed catalysts with finely-tuned metal-support interactions for stabilizing the most interfacial active metal species in diverse heterogeneous catalytic reactions.

Effect of yttrium addition on water-gas shift reaction over CuO/CeO_2 catalysts

This paper presented a study on the role of yttrium addition to CuO/CeO2 catalyst for water-gas shift reaction. A single-step co-precipitation method was used for preparation of a series of yttrium doped CuO/CeO2 catalysts with yttrium content in the range of 0-5wt.%. Properties of the obtained samples were characterized and analyzed by X-ray diffraction （XRD）, Raman spectroscopy, H2-TPR, cyclic voltammetry （CV） and the BET method. The results revealed that catalytic activity was increased with the yttrium content at first, but then decreased with the further increase of yttrium content. Herein, CuO/CeO2 catalyst doped with 2wt.% of yttrium showed the highest catalytic activity （CO conversion reaches 93.4% at 250 ℃） and thermal stability for WGS reaction. The catalytic activity was correlated with the surface area, the area of peak γ of H2-TPR profile （i.e., the reduction of surface copper oxide （crystalline forms） interacted with surface oxygen vacancies on ceria）, and the area of peak C2 and A1 （Cu^0→←Cu^2＋ in cyclic voltammetry process）, respectively. Besides, Raman spectra provided evidences for a synergistic Cu-Ovacancy interaction, and it was indicated that doping yttrium may facilitate the formation of oxygen vacancies on ceria.

Promotion effect of Re additive on the bifunctional Ni catalysts for methanation coupling with water gas shift of biogas: Insights from activation energy

The cheap manganese sand was first modified by H2O2 and was further creatively utilized as Ni-based catalyst support.In order to enhance the catalytic performance,Re was added into the Ni-based catalyst and the promotion effect of Re on the methanation coupling with water gas shift of biogas was investigated from the perspective of activation energy.It was found that CH4 and CO2 formation rates,which separately represented the reaction rate of methanation and water gas shift,were both enhanced after Re addition compared to non-added catalyst.Two kinetics models including empirical model and K-model were employed and from the results of calculation,it showed that Re selectively decreased the activation energy of methanation reaction and had little impact on the activation energy of water gas shift.The increased CO2 formation rate was owing to the assistance of accelerated H2O production from methanation rather than the activation energy change in water gas shift.

Graphene/carbon structured catalyst layer to enhance the performance and durability of the high-temperature proton exchange membrane fuel cells

In this study,nitrogen doped electrochemically exfoliated reduced graphene oxide and carbon black supported platinum(Pt/Nr EGO_(2)-CB_(3))has been prepared to enhance the performance and durability of hightemperature PEMFCs with lower Pt loading.On the one hand,Pt/Nr EGO_(2)-CB_(3)with the strong interaction between the Pt and nitrogen(N)prevent agglomeration of Pt particles and Pt particles is 5.46±1.46 nm,which is smaller than that of 6.78±1.34 nm in Pt/C.Meanwhile,ECSA of Pt/Nr EGO_(2)-CB_(3)decrease 13.65%after AST,which is much lower than that of 97.99%in Pt/C.On the other hand,the Nr EGO flakes in MEAac act as a barrier to mitigate phosphoric acid redistribution,which improves the formation of triple-phase boundaries(TPBs)and gives stable operation of the MEAacwith a lower decay rate of 0.02 mV h^(-1)within100 h.After steady-state operation,the maximum power density of Pt/Nr EGO_(2)-CB_(3)(0.411 W cm^(-2))is three times higher than that of conventional Pt/C(0.134 W cm^(-2))in high-temperature PEMFCs.After AST,the mass transfer resistance of Pt/Nr EGO_(2)-CB_(3)electrode(0.560Ωcm^(2))is lower than that in Pt/C(0.728Ωcm^(2)).

Effect of Mg/Al atom ratio of support on catalytic performance of Co-Mo/MgO-Al_2O_3 catalyst for water gas shift reaction

Co-Mo-based catalysts supported on mixed oxide supports MgO-Al2O3 with different Mg/Al atom ratios for water gas shift reaction were studied by means of TPR, Raman, XPS and ESR. It was found that the octahedral Mo species in oxidized Co-Mo/MgO（x）-Al2O3 catalyst and the contents of Mo^5＋, Mo^4＋, S^2- and S^2-2 species in the functioning catalysts increased with increasing the Mg/Al atom ratio of the support under the studied experimental conditions. This is favorable for the formation of the active Co-Mo-S phase of the catalysts. Catalytic performance testing results showed that the catalysts Co-Mo/MgO-Al2O3 with the Mg/Al atom ratio of the support in the range of 0.475-0.525 exhibited optimal catalytic activity for the reaction.

Effects of Cerium on Reduction of Non-Chromium Iron Based CO Shift Catalyst

The effects of Ce on reduction of non-chromium iron based CO shift catalyst were studied by XRD, TPR, SEM and XPS. The results show that Ce refines Fe2O3 grains and riches on the surface of catalyst in the process of reduction, which leads to decrease of the initial reductive temperature and increase of the final reductive temperature.

Computational Screening of Pt1@Ti_(3)C_(2)T_(2)(T=O,S)MXene Catalysts for Water-Gas Shift Reaction

Single-atom catalysts(SACs)provide an oppor-tunity to elucidate the catalytic mechanism of complex reactions in heterogeneous catalysis.The low-temperature water-gas shift(WGS)reaction is an important industrial technology to obtain high purity hydrogen.Herein,we study the catalytic activity of Pt1@Ti_(3)C_(2)T_(2)(T=O,S)SACs,where one subsurface Ti atom with three T vacancies in the functionalized Ti_(3)C_(2)T_(2)(T=O,S)MXene is substituted by one Pt atom,for the low-temperature show that Pt1@Ti_(3)C_(2)T_(2)provides an excellent platform for the WGS reaction by its bowl-shaped vacancy derived from the Pt1 single atom and three T defects surrounding it.Especially,Pt1@Ti_(3)C_(2)S_(2)SAC has higher catalytic performance for the WGS reaction,due to the weaker electronegativity of the S atom than the O atom,which significantly reduces the energy barrier of H*migration in the WGS reaction,which is often the rate-determining step.In the most favorable redox mechanism of the WGS reaction on Pt1@Ti_(3)C_(2)S_(2),the rate-determining step is the dissociation of OH*into O*and H*with the energy barrier as low as 1.12 eV.These results demonstrate that Pt1@Ti_(3)C_(2)S_(2)is promising in the application of MXenes for low-temperature WGS reactions.

Promoter effect on the CO_2-H_2O formation during Fischer-Tropsch synthesis on iron-based catalysts

The effects of Mg,La and Ca promoters on primary and secondary CO2 and H2O formation pathways during Fischer-Tropsch synthesis on precipitated Fe/Cu/SiO2 catalysts are investigated.The chemisorbed oxygen atoms in the primary pathway formed in the CO dissociation steps reacted with co-adsorbed hydrogen or carbon monoxide to produce H2O and CO2,respectively.The secondary pathway was the water-gas shift reaction.The results indicated that the CO2 production led to an increase in both primary and secondary pathways,and H2O production decreased when surface basicity of the catalyst increased in the order Ca 〉 Mg 〉 La.

High-temperature treatment to engineer the single-atom Pt coordination environment towards highly efficient hydrogen evolution

Development of high-performance and cost-effective catalysts for electrocatalytic hydrogen evolution reaction(HER)play crucial role in the growing hydrogen economy.Recently,the atomically dispersed metal catalysts have attracted increasing attention due to their ultimate atom utilization and great potential for highly cost-effective and high-efficiency HER electrocatalyst.Herein,we propose a hightemperature treatment strategy to furtherly improve the HER performance of atomically dispersed Ptbased catalyst.Interestingly,after appropriate high-temperature treatment on the atomically dispersed Pt0.8@CN,the Pt species on the designed N-doped porous carbon substrate with rich defect sites can be re-dispersed to single atom state with new coordination environment.The obtained Pt0.8@CN-1000 shows superior HER performance with overpotential of 13 m V at 10 m A cm^(-2)and mass activity of 11,284 m A/mgPtat-0.1 V,much higher than that of the pristine Pt0.8@CN and commercial Pt/C catalyst.The experimental and theoretical investigations indicate that the high-temperature treatment induces the restructuring of coordination environment and then the optimized Pt electronic state leads to the enhanced HER performances.This work affords new strategy and insights to develop the atomically dispersed high-efficiency catalysts.

A Novel γ-Alumina Supported Fe-Mo Bimetallic Catalyst for Reverse Water Gas Shift Reaction

在反向的水气体，移动(RWGS ) 反应 CO2 被变换成能接着被用来生产象甲醇那样的有益的化学药品的公司。在现在的学习， Mo/Al2O3， Fe/Al2O3 和 Fe-Mo/Al2O3，催化剂是用受精方法的 synthesised。催化剂的结构用 X 光检查衍射(XRD ) 被学习， Brunauer-Emmett-Teller (赌注) 方法，诱导地联合的血浆原子排放分光计(ICP-AES ) ，温度规划了减小(H2-TPR ) ，公司化学吸着，精力散 X 光检查(EDX ) 和扫描电子显微镜学(SEM ) 技术。所有催化剂的运动性质为 RWGS 反应在一个批反应堆被调查。结果显示在 Fe-Mo/Al2O3 催化剂的结构的那瞬间存在作为与 Fe/Al2O3 相比提高它的活动。这改进可能由于更好的 Fe 分散和 Fe 种类的更小的粒子尺寸。Fe-Mo/Al2O3 催化剂的稳定性测试在一个固定的床反应堆和高公司收益被执行因为溪流上的时间的 60 h 被表明。3 阶段在新鲜、使用的催化剂的结构被发现的 Fe2 (MoO4 ) 。TPR 结果也显示 3 分阶段执行的 Fe2 (MoO4 ) 有低 reducibility，因此， 3 显著地分阶段执行的 Fe2 (MoO4 ) 在催化剂禁止留下的 Fe 氧化物的减小，导致了 Fe-Mo/Al2O3 的高稳定性催化剂。总的来说，这研究与高公司产量作为新奇催化剂介绍 Fe-Mo/Al2O3，几乎没有副产品并且为 RWGS 反应相当稳定。

Kinetics of the water-gas shift reaction in Fischer-Tropsch synthesis over a nano-structured iron catalyst

Based on formate and direct oxidation mechanisms,three Langmuir-Hinshelwood-Hougen-Watson （LHHW） kinetic models of the water-gasshift （WGS） reaction over a nano-structured iron catalyst under Fischer-Tropsch synthesis （FTS） reaction conditions were derived and compared with those over the conventional catalyst.The conventional and nanostructured Fe/Cu/La/Si catalysts were prepared by co-precipitation of Fe and Cu nitrates in aqueous media and water-oil micro-emulsion,respectively.The WGS kinetic data were measured by experiments over a wide range of reaction conditions and comparisons were also made for various rate equations.WGS rate expressions based on the formate mechanism with the assumption that the formation of formate is rate determining step were found to be the best.

Potassium-decorated active carbon supported Co-Mo-based catalyst for water-gas shift reaction

The effect of potassium-decoration was studied on the activity of water-gas shift （WGS） reaction over the Co-Mo-based catalysts supported on active carbon （AC）, which was prepared by incipient wetness co-impregnation method. The decoration of potassium on active carbon in advance enhances the activities of the CoMo-K/AC catalysts for WGS reaction. Highest activity （about 92% conversion） was obtained at 250 ？ C for the catalyst with an optimum K 2 O/AC weight ratio in the range from 0.12 to 0.15. The catalysts were characterized by TPR and EPR, and the results show that activated carbon decorated with potassium makes Co-Mo species highly dispersed, and thus easily reduced and sulfurized. XRD results show that an appropriate content of potassium-decoration on active carbon supports may favors the formation of highly dispersed Co 9 S 8 -type structures which are situated on the edge or a site in contact with MoS 2 , K-Mo-O-S, Mo-S-K phase. Those active species are responsible for the high activity of CoMo-K/AC catalysts.

Influence of Gas Components on the Formation of Carbonyl Sulfide over Water-Gas Shift Catalyst B303Q

Water-gas shift reaction catalyst at lower temperature （200-400 ℃） may improve the conversion of carbon monoxide. But carbonyl sulfide was found to be present over the sulfided cobaltmolybdenum/alumina catalyst for water-gas shift reaction. The influences of temperature, space velocity, and gas components on the formation of carbonyl sulfide over sulfided cobalt-molybdenum/alumina catalyst B303Q at 200-400 ℃ were studied in a tubular fixed-bed quartz-glass reactor under simulated water-gas shift conditions. The experimental results showed that the yield of carbonyl sulfide over B303Q catalyst reached a maximum at 220 ℃ with the increase in temperature, sharply decreased with the increase in space velocity and the content of water vapor, increased with the increase in the content of carbon monoxide and carbon dioxide, and its yield increased and then reached a stable value with the increase in the content of hydrogen and hydrogen sulfide. The formation mechanism of carbonyl sulfide over B303Q catalyst at 200-400 ℃ was discussed on the basis of how these factors influence the formation of COS. The yield of carbonyl sulfide over B303Q catalyst at 200-400 ℃ was the combined result of two reactions, that is, COS was first produced by the reaction of carbon monoxide with hydrogen sulfide, and then the as-produced COS was converted to hydrogen sulfide and carbon dioxide by hydrolysis. The mechanism of COS formation is assumed as follows： sulfur atoms in the Co9Ss-MoS2/Al2O3 crystal lattice were easily removed and formed carbonyl sulfide with CO, and then hydrogen sulfide in the water-gas shift gas reacted with the crystal lattice oxygen atoms in CoO-MoOa/Al2O3 to form Co9S8-MoS2/Al2O3. This mechanism for the formation of COS over water-gas shift catalyst B303Q is in accordance with the Mars-Van Krevelen＇s redox mechanism over metal sulfide.

Performance and Industrial Application of New-Type Sulfur Tolerant CO Shift Catalyst QDB-04

This paper presents the performance and characteristics of new-type sulfur tolerant shift catalyst QDB-04 and its industrial side-line test as well as the first-time industrial application in Lunan Chemical Fertilizer Plant of Shandong in China. The results show that the catalyst has high strength and strength stability, good low temperature activity and stability as well as low potassium bleeding ratio which well meet for the requirements of the methanol plant on catalyst performance in Lunan Chemical Fertilizer Plant.