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.

For more and purer hydrogen-the progress and challenges in water gas shift reaction

The water gas shift(WGS) reaction is a standard reaction that is widely used in industrial hydrogen production and removal of carbon monoxide. The improved catalytic performance of WGS reaction also contributes to ammonia synthesis and other reactions. Advanced catalysts have been developed for both high and low-temperature reactions and are widely used in industry. In recent years, supported metal nanoparticle catalysts have been researched due to their high metal utilization. Low-temperature catalysts have shown promising results, including high selectivity, high shift rates, and higher activity potential. Additionally, significant progress has been made in removing trace CO through the redox reaction in electrolytic cell. This paper reviews the development of WGS reaction catalysts, including the reaction mechanism, catalyst design, and innovative research methods. The catalyst plays a crucial role in the WGS reaction, and this paper provides an instant of catalyst design under different conditions. The progress of catalysts is closely related to the development of advanced characterization techniques.Furthermore, modifying the catalyst surface to enhance activity and significantly increase reaction kinetics is a current research direction. This review goals to stimulate a better understanding of catalyst design, performance optimization, and driving mechanisms, leading to further progress in this field.

Reverse water gas shift reaction over Co-precipitated Ni-CeO_2 catalysts

The Ni-CeO2 catalysts with different Ni contents were prepared by a co-precipitation method and used for Reverse Water Gas Shift （RWGS） reaction. 2wt.%Ni-CeO2 showed excellent catalytic performance in terms of activity, selectivity, and stability for RWGS reaction. Characterizations of the catalyst samples were conducted by XRD and TPR. The results indicated that, in Ni-CeO2 catalysts, there were three kinds of nickel, nickel ions in ceria lattice, highly dispersed NiO and bulk NiO. Oxygen vacancies were formed in CeO2 lattice due to the incorporation of Ni^2＋ ions into ceria lattice. Oxygen vacancies formed in ceria lattice and highly dispersed Ni were key active components for RWGS, and bulk Ni was key active component for methanation of CO2.

La_(2-x)CexCu_(1-y)Zn_yO_4 perovskites for high temperature water-gas shift reaction

The performance of La2-xCexCu1-yZnyO4 perovskites as catalysts for the high temperature water-gas shift reaction （HT-WGSR） was investigated. The catalysts were characterized by EDS, XRD, BET surface area, TPR, and XANES. The results showed that all the perovskites exhibited the La2CuO4 orthorhombic structure, so the Pechini method is suitable for the preparation of pure perovskite. However, the La1.90Ce0.10CuO4 perovskite alone, when calcined at 350/700℃, also showed a （La0.935Ce0.065）2CuO4 perovskite with tetragonal struc- ture, which produced a surface area higher than the other perovskites. The perovskites that exhibited the best catalytic performance were those calcined at 350/700℃ and, among these, La1.90Ce0.10CuO4 was outstanding, probably because of the high surface area associated with the presence of the （La0.935Ce0.065）2CuO4 perovskite with tetragonal structure and orthorhombic La2CuO4 phase.

Copper Promoted Au/ZnO-CuO Catalysts for Low Temperature Water-gas Shift Reaction

Various copper promoted Au/ZnO-CuO catalysts with different atomic ratios of Cu to Zn prepared by means of co-precipitation were tested for the low temperature water-gas shift（WGS） reaction. The catalytic activity of the catalyst depends largely on the ratio of Cu to Zn. The addition of an appropriate amount of copper can considerably improve both the catalytic activity and the stability of the catalyst in comparison with those of copper-free Au/ZnO cata- lysts. The enhanced reducibility of copper oxide in the Au/ZnO-CuO ternary-component catalysts, which was confirmed by H2-TPR, may be related to the high activity and stability of the catalyst for the low temperature WGS reaction.

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.

Effects of the partial replacement of La by M(M=Ce,Ca and Sr) in La_(2-x)M_xCuO_4 perovskites on catalysis of the water-gas shift reaction

The performance of La2-x M x CuO4 perovskites （where M=Ce,Ca or Sr） as catalysts for the water-gas shift reaction was investigated at 290℃ and 360℃.The catalysts were characterized by EDS,XRD,N2 adsorption-desorption,XPS and XANES.The XRD results showed that all the perovskites exhibited a single phase （the presence of perovskite structure）,suggesting the incorporation of metals in the perovskite structure.The XPS and XANES results showed the presence of Cu2＋ on the surface.The perovskites that exhibited the best catalytic performance were La 2 x Ce x CuO 4 perovskites,with CO conversions of 85% 90%.Moreover,these perovskites have higher surface areas and larger amounts of Cu on the surface.And Ce has a higher filled energy level than the other metals,increasing the energy of the valence band of Ce and providing more electrons for the reaction.Besides,the La1.80Ca0.20CuO4 perovskite showed a good catalytic performance.

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.

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.

Selective synthesis of carbon monoxide via formates in reverse water–gas shift reaction over alumina-supported gold catalyst

Thermal decomposition of formic acid on SiO2, CeO2 and γ-Al2O3 was studied as an elementary step of reverse water–gas shit reaction（RWGS） over supported Au catalysts. γ-Al2O3 showed the highest CO selectivity among the tested oxides in the decomposition of formic acid. Infrared spectroscopy showed the formation of four formate species on γ-Al2O3： three η~1-type and one μ~2-type species, and these formates decomposed to CO at 473 K or higher. Au-loaded γ-Al2O3 samples were prepared by a depositionprecipitation method and used as catalysts for RWGS. The supported Au catalyst gave CO with high selectivity over 99% from CO2 and H2, which is attributed to the formation of formates on Au and subsequent decomposition to CO on γ-Al2O3.

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。

Insight into the Role of Isolated Gold Atoms-Ceria Conjunction in Catalyzing the Water-Gas Shift Reaction

As the promising catalysts for the water-gas shift(WGS)reaction,the activity of Au-CeO_(2) composites is susceptible to the aggregation size and electronic state of Au species.Previous reports were extensively focused on the discrepancy between nonmetallic Au and metallic Au nanoparticles,whereas the understanding of the authentic role of the isolated Au atoms was limited.Herein,we investigated the catalytic behavior and structural information over two types of Au/CeO_(2) catalysts,in which the predominant conjunctions were isolated Au1-CeO_(2) and Aun-CeO_(2),respectively.Based on comprehensive characterizations,particularly by in-situ Raman and in-situ DRIFTS,we found that the isolated Au atoms were responsible for enhancing the reducibility of the CeO_(2) matrix.The CO adsorption ability on the isolated Au sites was significantly inferior to clustered Au atoms,especially at relatively high temperatures(>200°C).As a result,the boosted O vacancy on the isolated Au1-CeO_(2) conjunctions could improve the H2O activation ability for the Au-CeO_(2) catalysts and demonstrate a comparable activity to the clustered Aun-CeO_(2) sites.This work might deepen understanding of the catalytic function for the isolated Au1 site within Au/CeO_(2) systems while catalyzing the WGS reaction.

Theoretical and experimental investigations on single-atom catalysis:Pt1/FeOx for water-gas shift reaction Shan-Fei Wang1,§,Yangyang Li2,3,§,Haiyan Wang1,Jin-Xia Liang1(✉),Chun Zhu1

Oxide-supported metal single-atom catalysts(SACs)have exhibited excellent catalytic performance for water-gas shift(WGS)reaction.Here,we report the single-atom catalyst Pt1/FeOx exhibits excellent medium temperature catalytic performance for WGS reactions by the density functional theory(DFT)calculations and experimental results.The calculations indicate that H_(2)O molecules are easily dissociated at oxygen vacancies,and the formed*OH and*O are adsorbed on Pt1 single atoms and the adjacent O atoms,respectively.After studying four possible reaction mechanisms,it is found that the optimal WGS reaction pathway is proceeded along the carboxyl mechanism(pathway III),in which the formation of*COOH intermediates can promote the stability of Pt1/FeOx SAC and the easier occurrence of WGS reaction.The energy barrier of the rate-determining step during the entire reaction cycle is only 1.16 eV,showing the high activity for the medium temperature WGS reaction on Pt1/FeOx SAC,which was verified by experimental results.Moreover,the calculated turnover frequencies(TOFs)of CO_(2)and H_(2)formation on Pt1/FeOx at 610 K(337℃)can reach up to 1.14×10^(-3)s^(-1)·site^(-1)through carboxyl mechanism.In this work,we further expand the application potential of Pt1/FeOx SAC in WGS reaction.

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.

Effect of precipitants on Ni-CeO_2 catalysts prepared by a co-precipitation method for the reverse water-gas shift reaction

A series of Ni-CeO2 catalysts were prepared by co-precipitation method with Na2CO3, NaOH, and mixed precipitant （Na2CO3：NaOH; 1：1 ratio） as precipitant, respectively. The effect of the precipitants on the catalytic performance, physical and chemical properties of Ni-CeO2 catalysts was investigated with the aid of X-ray diffraction （XRD）, Bmmaner-Emmett-Teller method （BET）, Fou- rier-transform infrared spectroscopy （FT-IR）, thermogravimetry （TG）, and H2-TPR characterizations. The Ni-CeO2 catalysts were exam- ined with respect to their catalytic performance for the reverse water-gas shift reaction, and their catalytic activities were ranked as： Ni-CeO2-CP （Na2CO3：NaOH=I：I）〉Ni-CeO2-CP（Na2CO3）〉Ni-CeO2-CP（NaOH）- Correlating to the characteristic results, it was found that the catalyst prepared by co-precipitation with mixed precipitant （Na2CO3：NaOH; 1：1 ratio） as precipitant hadthe most amount of oxygen vacancies accompanied with highly dispersed Ni particles, which made the corresponding Ni-CeO2-CP（Na2CO3：NaOH=I： 1） catalyst exhibit the highest catalytic activity. While the precipitant of Na2CO3 or NaOH resulted in less or no oxygen vacancies in Ni-CeO2 catalysts. As a result, Ni-CeO2-CP（Na2CO3） and Ni-CeO2-CP（NaOH） catalysts presented poor catalytic performance.

Influence of preparation method on performance of Ni-CeO_2 catalysts for reverse water-gas shift reaction

This study investigated 1 wt.% Ni-CeO2 catalysts that were prepared using co-precipitation, deposition-precipitation, and impregnation methods for the reverse water-gas shift （RWGS） reaction. Characterizations of the catalyst samples were conducted by Brumauer-Emmett-Teller （BET）, atomic absorption spectrophotometer （AAS）, X-ray diffraction （XRD）, transmission electron microscopy （TEM）, high-resolution transmission electron microscopy （HR-TEM） and temperature programmed reduction （TPR）. The results showed that the Ni-CeO2 catalyst prepared using the co-precipitation method exhibited the best catalytic performance. In the Ni-CeO2 catalyst prepared using co-precipitation method, a combination of highly dispersed NiO and abundant oxygen vacancies was assumed to play a crucial role in determining the catalytic activity and selectivity of the RWGS reaction.

Effect of doping rare earth oxide on performance of copper-manganese catalysts for water-gas shift reaction

Rare earth-doped copper-manganese mixed oxide catalysts were prepared by coprecipitation and mechanical mixing using copper sulfate, manganese sulfate, and rare-earth oxides REO （REO indicates La2O3, CeO2, Y2O3, or Pr6O11） as raw materials. The samples were characterized by X-ray diffraction （XRD）, temperature-programmed reduction （TPR）, temperature-programmed reduc-tion of oxidized surfaces （s-TPR）, and temperature-programmed desorption （TPD）. Catalytic activities were tested for a water-gas shift reaction. Doping rare earth oxides did not alter the crystal structure of the original copper-manganese mixed oxides but changed the interplanar spacing, adsorption performance and reaction performance. Doping with La2O3 enhanced the activity and stability of Cu-Mn mixed oxides because of high copper distribution and fine reduction. Doping with CeO2 and Y2O3 also decreased the reduc-tion temperatures of the samples to different degrees while improving the dispersion of Cu on the surface, thus, catalytic activity was better than that of undoped Cu-Mn sample. The Pr6O11-doped sample was difficult to reduce, the dispersion of surface coppers was lowered, resulting in poor activity.

Atomic-layered Au clusters on α-MoC as catalysts for the low-temperature water-gas shift reaction

Subject Code:B03With the support by the National Natural Science Foundation of China,a collaborative study by the research groups led by Prof.Ma Ding(马丁)from Peking University,Senior Scientist JoséA.Rodriguez from Brookhaven National Laboratory and Prof.Shi Chuan(石川)from Dalian University of

Atomically dispersed copper species on ceria for the low-temperature water-gas shift reaction

The structure of copper species,dispersed on nanostructured ceria(particles,rods and cubes),was analyzed by scanning transmission electron microscopy(STEM)and X-ray photoelectron spectroscopy(XPS).It was interestingly found that the density of surface oxygen vacancies(or defect sites),induced by the shape of ceria,determined the geometrical structure and the chemical state of copper species.Atomically dispersed species and monolayers containing few to tens of atoms were formed on ceria particles and rods owing to the enriched anchoring sites,but copper clusters/particles co-existed,together with the highly dispersed atoms and monolayers,on cubic ceria.The atomically dispersed copper sites and monolayers interacted strongly with ceria,involving a remarkable charge transfer from copper to ceria at their interfaces.The activity for the low-temperature watergas shift reaction of the Cu/CeO_(2) catalysts was associated with the fraction of the positively-charged copper atoms,demonstrating that the active sites could be tuned by dispersing Cu species on shape-controlled ceria particles.

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 CO_(2)utilization.Herein,Ni-and NiCe-containing hexagonal mesoporous silica(Ni-HMS and NiCe-HMS)catalysts were synthesized using an insitu one-pot method and applied for RWGS reaction.At certain reaction temperatures 500-750℃,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,H_(2)-TPR,CO_(2)-TPD,EPR and N_(2) adsorption-desortion technology.It was found that introduction of Ce created high concentration of oxygen vacancies,served as the active site for activating CO_(2).Also,this work analyzed the effect of the H_(2)/CO_(2)molar ratio on the best NiCe-HMS.When reaction gas H_(2)/CO_(2)molar ratio was 4 significantly decreased the selectivity to CO at low temperature,but triggered a higher CO_(2)conversion which is close to the equilibrium.