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.

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.

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.

Direct identification of the carbonate intermediate during water-gas shift reaction at Pt-NiO interfaces using surface-enhanced Raman spectroscopy

Noble metal-reducible oxide interfaces have been regarded as one of the most active sites for water-gas shift reaction.However,the molecular reaction mechanism of water-gas shift reaction at these interfaces still remains unclear.Herein,water-gas shift reaction at Pt-NiO interfaces has been in-situ explored using surface-enhanced Raman spectroscopy by construction of Au@Pt@NiO nanostructures.Direct Raman spectroscopic evidence demonstrates that water-gas shift reaction at Pt-NiO interfaces proceeds via an associative mechanism with the carbonate species as a key intermediate.The carbonate species is generated through the reaction of adsorbed CO with gaseous water,and its decomposition is a slow step in water-gas shift reaction.Moreover,the Pt-NiO interfaces would promote the formation of this carbonate intermediate,thus leading to a higher activity compared with pure Pt.This spectral information deepens the fundamental understanding of the reaction mechanism of water-gas shift reaction,which would promote the design of more efficient catalysts.

Preparation and characterization of Cu-Ce-La mixed oxide as water-gas shift catalyst for fuel cells application

Cu-Ce-La mixed oxides were prepared by three precipitation methods （coprecipitation, homogeneous precipitation, and deposition precipitation） with variable precipitators and characterized using X-ray diffraction, BET, temperature-programmed reduction, and catalytic reaction for the water-gas shift. The Cu-Ce-La mixed oxide prepared by coprecipitation method with NaOH as precipitator presented the highest activity and thermal stability. Copper ion substituted quadrevalent ceria entered CeO2 （111） framework was in favor of activity and thermal stability of catalyst. The crystallinity of fresh catalysts increased with the reduction process. La^3＋ or Ce^4＋ substituted copper ion entered the CeO2 framework during reduction process. The coexistence of surface copper oxide （crystalline） and pure bulk crystalline copper oxide both contributed to the high activity and thermal stability of Cu-Ce-La mixes oxide catalyst.

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.

Pt single atoms in oxygen vacancies boost reverse water-gas shift reaction by enhancing hydrogen spillover

The construction of synergistic catalysis of single atom catalysts(SACs)and oxygen vacancies(OV)on supports is crucial for the enhancement of heterogeneous catalytic efficiency,yet presents considerable challenges.Herein,we have developed an amine-molecule-assisted in-situ anchoring strategy that effectively stabilizes Pt SACs on OV sites of reduced TiO_(2)(TiO_(2)–x)by controlling the interaction of amine with Pt species and TiO_(2)–x.Direct evidence indicates that Pt SACs are anchored on the OV with forming Ptδ+–OV–Ti3+sites and strong metal-support interaction,which not only prevents the sintering of Pt SACs under high-temperature reduction treatments,but also enhances the hydrogen spillover process to facilitate the formation of more OV sites.During the reverse water-gas shift(RWGS)reaction,the enhanced amount of OV sites can increase CO_(2)adsorption,while the Pt SACs can efficiently promote the activation and spillover of hydrogen.Their combined synergistic effects greatly improve its catalytic performance with a high turnover frequency(TOF)of 9289 h−1 at 330℃ and notable stability for over 200 h,surpassing those of Pt clusters and nanoparticles on TiO_(2)–x.This work provides a new avenue for the controllable synthesis of synergistic catalysts with SACs and OV,significantly advancing catalytic efficiency.

Theoretical and experimental investigations on single-atom catalysis:Pt_(1)/FeO_(x) for water-gas shift reaction

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 Pt_(1)/FeO_(x) 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 Pt_(1)/FeO_(x) 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.

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 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.

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.

Theoretical and Experimental Study on Reaction Coupling: Dehydrogenation of Ethylbenzene in the Presence of Carbon Dioxide

Dehydrogenation of ethylbenzene （EB） to styrene （ST） in the presence of CO2, in which EB dehydrogenation is coupled with the reverse water-gas shift （RWGS）, was investigated extensively through both theoretical analysis and experimental characterization. The reaction coupling proved to be superior to the single dehydrogenation in several respects. Thermodynamic analysis suggests that equilibrium conversion of EB can be improved greatly by reaction coupling due to the simultaneous elimination of the hydrogen produced from dehydrogenation. Catalytic tests proved that iron and vanadium supported on activated carbon or Al2O3 with certain promoters are potential catalysts for this coupling process. The catalysts of iron and vanadium are different in the reaction mechanism, although ST yield is always associated with CO2 conversion over various catalysts. The two-step pathway plays an important role in the coupling process over Fe/Al2O3, while the one-step pathway dominates the reaction over V/Al2O3. Coke deposition and deep reduction of active components are the major causes of catalyst deactivation. CO2 can alleviate the catalyst deactivation effectively through preserving the active species at high valence in the coupling process, though it can not suppress the coke deposition.

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

Identifying the roles of Ce^(3+)-OH and Ce-H in the reverse water-gas shift reaction over highly active Ni-doped CeO_(2) catalyst

Nickel-CeO_(2)-based materials are commonly used for the thermal catalytic hydrogenation of CO_(2).However,high Ni loadings and low CO selectivity restrict their use in the reverse water–gas shift(RWGS)reaction.Herein,we demonstrate a highly active,robust,and low-Ni-doped(1.1 wt.%)CeO_(2) catalyst(1.0-Ni-CeO_(2)).The Ni-based-mass-specific CO formation rate reaches up to 1,542 mmol·gNi^(−1)·h^(−1) with 100%CO selectivity at 300°C for 100 h,among the best values reported in the literature.Density functional theory(DFT)and diffuse reflectance infrared Fourier transform spectroscopy(DRIFTS)results reveal that the enhanced catalytic activity is attributed to the abundant Ce–H species,while the high selectivity results from low CO affinity.More importantly,a new reaction mechanism is proposed,which involves the reduction of bicarbonate to generate formate intermediate and CO by the H−released from Ce–H species.The new findings in this work will benefit the design of economic,efficient,and robust catalysts for low-temperature RWGS reactions.

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.

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77.15eV,d带中心为-3.18eV。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77.99eV,且d带中心为-3.05eV,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4.84eV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。

对失活Co-Mo-KAl_2O_3硫化物催化剂的剖析研究

本文通过多种测试技术研究了工业Co -Mo -K Al2 O3 耐硫变换催化剂 ,失活样中各元素的存在状态、含量和物相变化。发现 ,在原催化剂中钾、硫从内部向表面迁移并有流失 ,γ -Al2 O3 转变为 (Al2 O3 ) 10R ,MoS2 、Co9S8变为含活性硫物种少的物相 ;从反应气中夹带的铁、铬、硅和镍杂质沉积在表面上。由此导致催化剂对H2 O和CO的吸附与反应能力的下降 ,最终造成严重失活。

铜锰氧化物水煤气变换催化剂的还原与催化性能

以CuSO4.5H2O和MnSO4.H2O为前驱物,NaOH为沉淀剂,选用共沉淀工艺,添加Al2O3、BaO+Al2O3、ZrO2+Al2O3或CeO2+Al2O3粉末作为催化助剂,制备了4种铜锰氧化物水煤气高温变换催化剂。X射线衍射分析表明,4种铜锰氧化物催化剂的主要化学成分为氧化铜和氧化锰系化合物以及锰钡、铜锰和铜锰铝复合氧化物;在催化水煤气变换反应(WGSR)后,4种铜锰氧化物的化学成分发生了变化。H2还原实验结果表明,在4种铜锰氧化物中,添加ZrO2+Al2O3的铜锰氧化物H2还原效率最好;而添加CeO2+Al2O3的铜锰氧化物H2还原效率最小。对WGSR出口气中CO体积分数进行对比分析可知,分别添加Al2O3和CeO2+Al2O3铜锰氧化物催化剂的变换活性较好。

金基二元合金团簇Au_(12)M(M=Cu,Pt,Ni)催化水煤气变换反应的理论研究

利用密度泛函理论(DFT)对Au12M(M=Cu,Pt,Ni)3种合金团簇的结构稳定性、热力学稳定性和反应活性进行研究,并对金基二元合金团簇催化水煤气变换反应(WGSR)的反应机理进行探讨.研究发现,Au12Ni合金团簇的稳定性及电子活性最优.考察了WGSR在金基二元合金团簇上的氧化还原机理和羧基机理,表明Au12Cu合金团簇上WGSR按照氧化还原机理A进行,水解离后产生的OH*会继续解离为O*和H*(*代表吸附物质);Au12Pt及Au12Ni合金团簇上按照氧化还原机理B进行,2个OH*发生歧化反应.比较3种团簇上的最佳反应路径发现,Au12Cu团簇对WGSR表现出较好的催化活性.

新型钴钼系耐硫变换催化剂本征动力学

采用等温管式积分反应器,在(550～750)K、(2.0～3.5)MPa和空速(15～30)L.(g.h)-1条件下,对新型钴钼系耐硫变换催化剂进行变换反应本征动力学研究。建立了包含压力项的幂函数型动力学模型,根据实验测定数据,结合具有全局寻优能力微粒群算法和求解微分方程的龙格-库塔法,通过迭代寻优对变换反应动力学模型进行参数估计,获得高度显著、可信的动力学模型:r=-(dNCO)/(dW)=39981.876exp(-(68424.0)/(RT))PCO0.4176PH2O0.9297PCO2-0.5516PH2-0.7503(1-β)。结果表明,在催化剂上进行变换反应时,反应速率对CO组分分压变化的敏感性较低,H2O组分分压对反应速率的影响较大,高汽气比下催化活性较高。