Influence of cobalt on performance of Cu-CeO_2 catalysts for preferential oxidation of CO

Copper and cobalt oxides supported on CeO_2 were investigated for preferential oxidation of carbon monoxide(CO-PROX) in the presence of excess hydrogen and CO_2.(Cuo)_(1-x)(Co_3 O_4)_(x/3)-(CeO_2)_(2.5)(x=0,0.25,0.50,0.75,0.85 and 1) catalysts were prepared by coprecipitation method.These mixed oxide catalysts were characterized by several physicochemical techniques,such as BET surface area(S_(BET)),X-ray diffraction(XRD),high resolution transmission electron microscopy(HRTEM),temperature programmed reduction(TPR) and X-ray photoelectron spectroscopy(XPS).XRD studies show the peaks related to CuO and Co_3 O_4 phases in copper and cobalt containing CeO_2 catalysts.The average particle size of the CeO_2 crystallites is in the range of 8-10 nm as evaluated from HRTEM studies.XPS studies demonstrate that Cu,Co and Ce in(cuO)_(1-x)(Co_3O_4)_(x/3)-(CeO_2)_(2.5) catalysts are presented in+2 and +1,+3 and +2 and +4 and +3 oxidation states,respectively.The catalyst with x=0.75 shows better activity and selectivity towards CO-PROX.Though the catalyst with only copper(CuO-CeO_2,x=0) shows good activity but reverse water gas shift(RWGS) reaction is noticed at high temperature.On the other hand,RWGS reaction is suppressed on the cobalt containing CuO-ceO_2 catalyst.Cobalt on CeO_2 with x=1 shows hardly any activity for PRoX reaction at low temperatures.No methanation activity is observed on CuO-CeO_2 or Co_3O_4-CeO_2 catalysts.In contrast,combination of copper and cobalt on CeO_2 shows methanation of CO where enhanced activity is observed with increasing in cobalt content.     

Effect of PdO_x structure properties on catalytic performance of Pd/Ce_(0.67)Zr_(0.33)O_2 catalyst for CO,HC and NO_x elimination

Pd/Ce_(0.67)Zr_(0.33)O_2 catalyst was pretreated in different atmosphere respectively, and characterized by CO chemical adsorption, XPS, HR-TEM, H_2-TPR, Raman, OSC and in situ DRIFTS to investigate the effect of the structure properties of PdO_x species on the catalytic performance for CO, HC and NO_x elimination. The results show that Pd/CZ catalyst pretreated in air atmosphere has higher oxidation activity of HC due to having high Pd dispersion and strong interaction between PdO_x and CZ support. Pd/CZ-H catalyst pretreated in reducing atmosphere exhibits better catalytic performance of NO_x elimination because of having relatively big Pd particle size, more Pd species in metallic state and higher concentration of oxygen vacancies. While for the Pd/CZ-RG catalyst pretreated in reactant atmosphere, strong adsorption of HC species on the surface of catalysts would lead to a part of active sites being covered, which inhibits HC and NO conversions.     

Influence of CeO_2 loading on structure and catalytic activity for NH_3-SCR over TiO_2-supported CeO_2

A series of supported CeO_2/TiO_2 catalysts were prepared to explore the influence of CeO_2 loading on these catalysts for the selective catalytic reduction of NO_3 by NH_3(NH_3-SCR).The catalysts were investigated in detail by means of XRD,Raman,H_2-TPR,NH_3-TPD,XPS,in situ DRIFTS,and NH3-SCR reaction.The activity of the catalyst is closely related to the content of CeO_2.When the loading of CeO_2 is near the dispersion capacity(1.16 mmol Ce~(4+)/100 m~2 TiO_2),the catalytic activity is better.This may be because that the dispersed CeO_2 is the active species and the catalyst has appropriate redox property,along with the larger amounts of surface Ce content and surface adsorbed oxygen species.Finally,a possible reaction mechanism via the Langmuir-Hinshelwood(L-H) mechanism is tentatively proposed to further understand the NH_3-SCR reaction.     

The variation of microstructures,spectral characteristics and catalysis effects of Fe~(3+) and Zn~(2+) co-doped CeO_2 solid solutions

Fe~(3+)and Zn~(2+)ions were doped into the lattice of CeO_2 via the hydrothermal method.The micro structure and spectra features were analyzed systemically.XRD results show that the solid solubility of Fe~(3+)and Zn~(2+)ions in Ce_(1-x)(Fe_(0.5)Zn_(0.5))_xO_2 can be identified as x=0.16.The cell volumes are decreased by increasing the doped content.The TEM graphs prove that the grain size of the sample is about 10 nm,and the EDS result indicates that the doped contents are in accordance with that of the theory concentrations.Meanwhile,the doping also causes the increasing concentrations of the defects and oxygen vacancies which are supported by the XPS,Raman,UV and PL characterizations.The samples exhibit better catalytic activities for improving the hydrogen storage properties and the electrochemical kinetics of the ball milled Mg_2Ni based composites.Further,the catalysis effects are improved by increasing the doped contents,which can be ascribed to the increasing contents of the oxygen vacancies,defects,the special electron transition states and the nature of the doped ions in CeO_2-based solid solutions.     

Catalytic oxidation of formaldehyde over CeO_2-Co_3O_4 catalysts

A series of CeO_2-Co_3O_4 mixed oxide catalysts with different Co/(Co+Ce) atomic ratios were synthesized by citric acid sol-gel method and used for catalytic oxidation of formaldehyde(HCHO). Many techniques such as Brumauer-Emmett-Teller(BET), X-ray diffraction(XRD), scanning electron microscopy(FE-SEM), temperature programmed reduction(H_2-TPR), temperature-programmed desorption(O_2-TPD) and X-ray photoelectron spectroscopy(XPS) were used to characterize catalysts. The results of catalytic performance tests showed that the catalyst CeO_2-Co_3O_4 with Co/(Co+Ce) ratio of 0.95 exhibited the best performance, and the temperature of complete oxidation of HCHO was 80 oC. The analytical results indicated that the addition of CeO_2 enhanced the specific surface area of Co_3O_4 and the fine dispersion of both of them. Moreover, the strong interaction between CeO_2 and Co_3O_4 resulted in the unique redox properties, which enhanced the available surface active oxygen and led to high valence state of cobalt oxide species. All those effects played crucial roles in the excellent performance of CeO_2-Co_3O_4 for the HCHO oxidation.     

Modification of Cu/ZSM-5 catalyst with CeO_2 for selective catalytic reduction of NO_x with ammonia

Cu/ZSM-5 and CeO_2-modified Cu/ZSM-5 catalysts were prepared by a wetness impregnation method. The addition of CeO_2 was found to enhance the NO_x selective catalytic reduction(SCR) activity of the catalyst at low temperatures, but the high-temperature activity was weakened. The catalysts were characterized by X-ray diffraction(XRD), nitrogen physisorption, inductively coupled plasma optical emission spectrometry(ICP-OES), X-ray photoelectron spectroscopy(XPS), electron paramagnetic resonance(EPR), H_2 temperature-programmed reduction(TPR) and NH_3 temperature-programmed desorption(TPD). The results showed that more CuO clusters instead of isolated Cu~(2+) species were obtained on the modified catalyst. These active CuO clusters, as well as the Cu-Ce synergistic effect, improved the redox property of the catalyst and low-temperatures SCR activity via promoting the oxidation of NO to NO_2 and fast SCR reaction. The loss in high-temperatures activity was attributed to the enhanced competitive oxidation of NH_3 by O_2 and decreased surface acidity of the catalyst.     

Effect of Ce doping into V_2O_5-WO_3/TiO_2 catalysts on the selective catalytic reduction of NO_x by NH_3

In this work, the effectiveness of V_2O_5-WO_3/TiO_2 catalysts modified with different CeO_2 contents by impregnation and co-precipitation methods on the selective catalytic reduction of NOxby NH3 have been studied comparatively by various experimental techniques. The results showed that the NO conversion of V_2O_5-WO_3/CeO_2-TiO_2 catalysts modified by co-precipitation method obviously increased with the Ce doping contents in the studied range below 20%(All Ce contents are in mass fractions), but the NO conversion of V_2O_5-WO_3/CeO_2/TiO_2 catalysts modified by impregnation methods was lower than V_2O_5-WO_3/CeO_2-TiO_2 catalysts especially beyond 2.5% Ce doping contents. The V_2O_5-WO_3/CeO_2-TiO_2 catalysts showed better SCR activity, wider reaction window, and higher sulfur and water resistance. The characterization results elucidated that the modified catalysts by co-precipitation method exhibited higher specific surface area, much better dispersity of Ce component, more Ce~(3+)species and more Br?nsted acid sites than that by impregnation. The vacancies caused by more Ce~(3+)species were favorable for more NO oxidation to NO_2, and the interaction between Ce species and WOxspecies generated more Br?nsted acid sites. It could be supposed that dispersed Ce Oxspecies and WOxspecies offered more second active centers respectively to adsorb oxygen and activate ammonia as co-catalysis to the primary active center of V ions, thus facilitated the better SCR activity of modified V_2O_5-WO_3/CeO_2-TiO_2 catalysts by coprecipitation methods. The co-precipitation methods with Ce component were more suitable for production of modified commercial V_2O_5-WO_3/TiO_2 catalysts.     

High activity of CeO_2-TiO_2 composites for deep oxidation of 1,2-dichloroethane

CeO_2-TiO_2 catalysts prepared by different methods were investigated for deep oxidation of 1,2-dichloroethane(DCE),as a typical representative of the chlorinated volatile organic compounds(CVOCs).Characterization analysis reveals that CeO_2-TiO_2 catalysts prepared by sol-gel and coprecipitation methods exhibit higher specific area,CeO_2 and TiO_2 particles are highly dispersed into each other and the reducibility and mobility of active oxygen species are obviously promoted due to the strong interaction between the two catalysts CeO_2 and TiO_2,resulting in higher catalytic activity for DCE oxidation to and less chlorinated byproduct.The high calcination temperature would lead to the formation of a new monoclinic phase Ce_(0.3)Ti_(0.7)O_2 and sintering,which is the main reason for the catalytic activity for DCE oxidation markedly decreases.     

CeO_2/CuO catalysts using different template agent for preferential CO oxidation in H_2-rich stream

The CeO_2/CuO catalysts using different template agent(F68 L64, F127 and P123) were synthesized by the simple template and impregnation method. They were characterized by FESEM, XRD, N2 physisorption and H2-TPR techniques. It is found that the CeO_2/CuO catalysts are double pore distribution, and CeO_2 can enter into the gap of CuO supports and form the contact interface of copper and cerium. Among the asprepared catalysts, the CeO_2/CuO-F127 catalyst displays better activity at lower temperature and the CeO_2/CuO-P123 catalyst presents higher activity at higher temperature. The CeO_2/CuO-P123 catalyst has the smallest crystallite sizes of CuO and CeO_2 as well as the largest size of cubes, which may improve the interaction of copper and cerium and enhance the performance of CO oxidation.     

CeO2with diverse morphologies-supported IrOx nanocatalysts for efficient oxygen evolution reaction—Commemorating the 100th anniversary of the birth of Academician Guangxian Xu

IrOx-based catalysts are considered the most promising candidates for oxygen evolution reaction(OER)due to their high efficiency.However,improving their intrinsic catalytic activity is essential for practical application.In this work,CeO₂with three different morphologies(rod,cube,octahedron)and supported IrOx nanoparticles were fabricated,and they display morphology-dependent OER activity.The IrOx/CeO₂-rod shows the highest activity;the catalysts have a catalytic activity sequence of rod>cube>octahedron.A plausible mechanism was proposed:the CeO₂support with different morphologies modulates the electronic structure of IrOx by the synergistic interaction promoted by oxygen vacancies between the active component and the support,thereby altering the catalytic activity of the IrOx/CeO₂catalyst.     

Cerium (Ⅳ) oxide nanocomposites:Catalytic properties and industrial application

This review article provides a new insight on the application of cerium oxide(CeO_2)-metal oxide nanocomposites as catalyst with enhanced reducibility and improved oxygen(O_2) storage capacity,especially in the varying chemical reaction processes including combustion,oxidation,epoxidation and redox.The CeO_2-metal oxide interaction plays an important role in controlling particle size,O_2 availability and coke resistance properties of the catalyst.Strong metal oxide-CeO_2 interaction also assists in generating small and highly dispersed particles,resists sintering of catalyst particles during the catalysis process,and consequently improves the O_2 availability of the catalyst.Indeed,CeO_2 not only provides an active support to heterogeneous catalyst,but also creates a new active site at the metal-support interface to produce stronger nanoparticle bonding through the surface O_2 vacancy.This consequently produces a heterogeneous catalytic system with promising reaction rate and catalytic stability in many industrial applications such as CO_2 hydrogenation,CO oxidatio n,biodiesel productio n,gas reduction,photocatalytic and methane steam reforming.     

Au-Pd/ZnO-CeO_2催化剂甲醇部分氧化制氢性能的研究

采用聚合物保护乙醇还原法制备了Au-Pd/ZnO-CeO_2催化剂,考察了CeO_2对Au-Pd/ZnO催化剂甲醇部分氧化制氢反应性能的影响,并运用BET、XRD、TPR、H_2-TPD和CH_3OH-TPD等手段对催化剂进行了表征.结果表明,CeO_2对Au-Pd/ZnO催化剂具有较好的改性效果,CeO_2的引入能提高Au-Pd/ZnO催化剂的活性和氢气的选择性,归结于CeO_2的加入增加了催化剂的比表面积、分散度和对反应物甲醇的吸附,同时减少了对生成物H_2脱附,这些均有利于甲醇部分氧化制氢反应.     

Effect of Rare Earth Oxides on Catalysts Mo-Te System

Surface compositions,structures,and acidities of the Mo-Te-Fe-Ni catalysts added with La_2O_3,CeO_2,Pr_6O_(12),Nd_2O_3 and Sm_2O_3 were measured and related with the activities of the catalysts for selective oxidationof olefins.It was found that adding rare earth elements to the Mo-Te catalysts increases obviously theirselectivities to methacrolein(MAL),and the yield percentage of MAL changes periodically with the increase ofatomic numbers of rare earth elements added,and the highest yield was obtained with the catalyst containingCeO_2.The addition of CeO_2 to 9-component Mo-Te catalyst increases not only the activity of the catalyst,but also its thermostability remarkably.The mechanism of rare earth elements in the catalysts was discussed.     

Influence of MnO2 modification methods on the catalytic performance of CuO/CeO2 for NO reduction by CO

In order to investigate the influence of MnO2 modification methods on the catalytic performance of CuO/CeO2 catalyst for NO reduction by CO,two series of catalysts(xCuyMn/Ce and xCu/yMn/Ce) were prepared by co-impregnation and stepwise-impregnation methods,and characterized by means of X-ray diffraction(XRD),Raman spectra,H2-temperature programmed reduction(H2-TPR),in situ diffuse reflectance infrared Fourier transform spectra(in situ DRIFTS) techniques.Furthermore,the catalytic performances of these catalysts were evaluated by NO+CO model reaction.The obtained results indicated that:(1) The catalysts acquired by co-impregnation method exhibited stronger interaction owing to the more sufficient contact among each component of the catalysts compared with the catalysts obtained by stepwise-impregnation method,which was beneficial to the improvement of the reduction behavior;(2) The excellent reduction behavior was conducive to the formation of low valence state copper species(Cu+/Cu0) and more oxygen vacancies(especially the surface synergetic oxygen vacancies(SSOV,Cu+-□-Mn(4–x)+)) during the reaction process,which were beneficial to the adsorption of CO species and the dissociation of NO species,respectively,and further promoted the enhancement of the catalytic performance.Finally,in order to further understand the difference between the catalytic performances of these catalysts prepared by co-impregnation and stepwise-impregnation methods,a possible reaction mechanism(schematic diagram) was tentatively proposed.     

Effect of yttrium addition on water-gas shift reaction over CuO/CeO2 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 y 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 (Cu0→Cu2+ 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.     

Construction of mesoporous ceria-supported gold catalysts with rich oxygen vacancies for efficient CO oxidation

Bearing unique redox nature and high oxygen storage capacity, ceria (CeO₂) has always been a promising CO oxidation catalyst support for gold (Au) catalysts and the like. Herein, a series of Au–CeO₂–P (P stands for pH value) samples was prepared by a co-precipitation method with the assistance of an alkaline environment and amino groups functionalized ordered mesoporous polymer (OMP-NH₂). Afterward, all samples described above were characterized that the Au–CeO₂–P catalysts are made of Au–Ce–O solid solution and Au nanoparticles (NPs) supported on CeO₂. It turns out that OMP-NH₂ is not just a simple sacrificial template for mesoporous structure, but also plays an important role as an amino source, explaining the presence of rich oxygen vacancies. Due to the concentration of oxygen vacancies in Au–Ce–O solid solution is the key factor for the oxygen mobility of CO oxidation, the catalytic results also demonstrate that the catalytic activity of Au–CeO₂–P catalysts is related to the concentration of their oxygen vacancies. Moreover, Au–CeO₂-9.6 with a highest concentration of oxygen vacancies (as high as 13.98%) in Au–CeO₂–P catalysts exhibits the best catalytic activity (complete conversion at 10 °C).     

Synthesis of mesoporous CeO2-MnOx binary oxides and their catalytic performances for CO oxidation

Mesoporous CeO2-MnOx binary oxides with different Mn/Ce molar ratios were prepared by hydrothermal synthesis and characterized by scanning electron microscopy （SEM）, N2 sorption, X-ray diffraction （XRD）, X-ray photoelectron spectroscopy （XPS） and H2 temperature-programmed reduction （H2-TPR）. The characterization results indicated that the CeO2-MnOx catalysts exhibited flower-like microspheres with high specific surface areas, and partial Mn cations could be incorporated into CeO2 lattice to form solid solution. The CeO2-MnOx catalysts showed better catalytic activity for CO oxidation than that prepared by the coprecipitation method. Furthermore, the CeO2-MnOx catalyst with Mn/Ce molar ratio of 1 in the synthesis gel （Ce-Mn-1） exhibited the best catalytic activity, over which the conversion of CO could achieve 90% at 135 ℃. This was ascribed to presence of more Mn species with higher oxida- tion state on the surface and the better reducibility over the Ce-Mn-I catalyst than other CeO2-MnOx catalysts.     

Effect of water vapor on the CO and CH4 catalytic oxidation over CeO2-Mox (M=Cu,Mn,Fe,Co,and Ni) mixed oxide

CeO2-MOx (M=Cu, Mn, Fe, Co, and Ni) mixed oxide catalysts were prepared by a citric acid complexation-combustion method. CeO2-MOx solid solutions could be formed with M cations doping into CeO2 lattice, while NiO and Co3O4 phases were detected on the surface of CeO2-NiO and CeO2-Co3O4 by Raman spectroscopy. The presence of M in CeO2 could obviously promote its catalytic activity for CH4 catalytic combustion and CO oxidation. Among the prepared samples, CeO2-CuO exhibited the best performance for CO oxidatio...     

Preparation and characteristics of nano-crystalline Cu-Ce-Zr-O composite oxides via a green route: supercritical anti-solvent process

The nano-crystalline Cu-Ce-Zr-O composite oxides were successfully prepared by the supercritical anti-solvent (SAS) process. The physicochemical properties and catalytic performances were investigated by X-ray diffraction (XRD), Raman spectroscopy, H2 temperature-programmed reduction (H2 -TPR), oxygen storage capacity (OSC) measurement and catalytic activity evaluation. It was found that Cu2+ ions incorporated into CeO2 -ZrO2 lattice to form Cu-Ce-Zr-O solid solution associated with the formation of oxygen vacancies. The Cu-Ce-Zr-O catalysts prepared via the SAS process with the Cu content 2.63 mol.% showed the highest OSC index of 636.9 μmol/g. Compared with the samples prepared by impregnation method, Cu doping using SAS process could improve the dispersion of Cu2+ in the composite oxide, enhance the interaction between Cu2+ and CeO2-ZrO2 , improve the reducibility of catalyst, and thus improve the OSC performance and increase the catalytic activity for CO oxidation at low temperature.     

Effect of CuO species and oxygen vacancies over CuO/CeO2 catalysts on low-temperature oxidation of ethyl acetate

The catalytic oxidation of ethyl acetate(EA) was studied over CuO/CeO₂ catalysts which were prepared by ball milling with different precursors(copper oxide,cerium acetate,cerium dioxide,copper acetate and cerium hydroxide).The CuO/CeO₂ catalyst(O-A) prepared with copper oxide and cerium acetate as precursors shows very high catalytic activity that 100% EA conversion is achieved at low temperature of 220℃.It is found that specific surface area(112.8 m²/g),particle...