Catalytic performance of Zr-doped CuO-CeO_2 oxides for CO selective oxidation in H_2-rich stream

Zr-doped CuO-CeO_2 catalysts for CO selective oxidation were designed and prepared by the hydrothermal method and coprecipitation. The experimental samples were characterized by means of N_2 adsorption-desorption isotherms, powder X-ray diffraction, temperature-programmed reduction and Xray photoelectron spectroscopy. It is observed that the catalyst prepared by hydrothermal method exhibits larger specific surface area, smaller crystalline size and higher dispersion of active components compared with those of the catalyst obtained by coprecipitation. Meanwhile, redox properties of copper oxide are improved significantly and highly dispersed copper species providing CO oxidation sites are present on the surface. Furthermore, adsorptive centers of CO and active oxygen species increase on the copper-ceria interfaces. The Zr-doped CuO-CeO_2 catalyst prepared by hydrothermal method possesses superior catalytic activity and selectivity for selective oxidation of CO at low temperature compared with those of the sample prepared by coprecipitation. The temperature corresponding to 50% CO conversion is only 73 ℃ and the temperature span of total CO conversion is expanded from 120 to 160 ℃.     

Ceria supported nickel catalysts for CO removal from H_2-rich gas

CO in H_2-rich gas must be removed to meet various requirements in industrial applications. Four methods, i.e., the precipitation method using aqueous ammonia, the complexing method using urea, the complexing method using citric acid and the precipitation method using ammonium carbonate, were adopted to prepare samples NiO/CeO_2 as catalyst precursors for removal of CO from H_2-rich gas via selective methanation reaction. The sample NiO/CeO_2 prepared by the precipitation method using aqueous ammonia as precipitant exhibited the highest catalytic activity both for CO methanation and for CO_2 methanation after reduction prior to the catalytic reaction. Chlorine ion was then doped to suppress CO_2 conversion. Effect of chlorine doping was investigated. Over the optimal catalyst 40%Ni(Cl_(0.2))/CeO_2, CO in the H_2-rich gas was removed to below 10 ppm with selectivity of 60% or higher at reaction temperatures 230–250 ℃ in the test period of 75 h.     

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.     

Support interaction of Pt/CeO_2 and Pt/SiC catalysts prepared by nano platinum colloid deposition for CO oxidation

The interaction between Pt and its various supports can regulate the intrinsic electronic structure of Pt particles and their catalytic performance.Herein,Pt/CeO_2 and Pt/SiC catalysts were successfully prepared via a facile Pt colloidal particle deposition method,and their catalytic performance in CO oxidation was investigated.XRD,TEM,XPS and H_2-TPR were used to identify the states of Pt particles on the support surface,as well as their effect on the performance of the catalysts.Formation of the Pt-O-Ce interaction is one of the factors controlling catalyst activity.Under the oxidative treatment at low temperature,the Pt-O-Ce interaction plays an important role in improving the catalytic activity.After calcining at high temperature,enhanced Pt-O-Ce interaction results in the absence of metallic Pt~0 on the support surface,as evidenced by the appearance of Pt~(2+) species.It is consistent with the XPS data of Pt/CeO_2,and is the main reason behind the deactivation of the catalyst.By contrast,either no interaction is formed between Pt and SiC or Pt nanoparticles remain in the metallic Pt~0 state on the SiC surface even after aging at 800℃in an oxidizing atmosphere.Thus,the Pt/SiC shows better thermal stability than Pt/CeO_2.The interaction between Pt and the active support may be concluded to be essential for CO oxidation at low temperature,but strong interactions may induce serious deactivation of catalytic activity.     

Effects of water on CO catalytic oxidation over Pd/CeO_2

The role of water in CO oxidation was investigated on Pd/CeO_2 with different morphologies(rods(R),cubes(C) and octahedrons(O)).Compared with the absence of water,CO oxidation activity increases 2 times in the presence of water on Pd/CeO_2-C;but a decrease is found on Pd/CeO_2-R.Catalyst characterization reveals that Pd is mainly in the form of solid solution(Pd_xCe_(1-x)O_(2-σ)) on Pd/CeO_2-R and a mixture of metal and Pd_xCe_(1-x)O_(2-σ) solid solution on Pd/CeO_2-C.The strong interaction between Pd and CeO_2-R results in the form of stable bidentate carbonates species;while the relatively weak interaction between Pd and CeO_2-C leads to the produce of unstable monodentate carbonates species.The effects of water on CO oxidation activity closely relate with the Pd chemical state and the types of carbonates species.Water restrains CO adsorption on Pd_xCe_(1-x)O_(2-σ) solid solution,but it has negligent effects on metallic Pd species.In the presence of water,bidentate carbonates species remains stable but the decrease in the amount of monodentate carbonates species is observed.     

CuO/m-Ce0.5Zr0.5O2催化剂和富氢条件下CO氧化性能的研究

采用多元醇法合成了介孔Ce0.5Zr0.5O2(m-Ce0.5Zr0.5O2)复合氧化物,研究了m-Ce0.5Zr0.5O2和焙烧温度对Cu基催化剂富氢条件下CO氧化性能的影响,并运用XRD、TPR、TPD、比表面和孔径测定等技术对载体及催化剂进行了表征.结果表明,多元醇法合成的m-Ce0.5Zr0.5O2具有较大比表面积和均一的立方萤石结构.与CuO/Ce0.5Zr0.5O2催化剂相比,CuO/m-Ce0.5Zr0.5O2催化剂具有较好的催化活性,归因于该催化剂具有较大的比表面积和高分散的CuO.焙烧温度对CuO/m-Ce0.5Zr0.5O2催化剂的性能有较大的影响,其中以673K焙烧所制备的催化剂活性最好.     

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...     

Barrier effect of SiO_2 shell over hollow CeO_2/CuO@SiO_2 catalysts for broadening temperature window of total CO conversion

The hollow inverse CeO_2/CuO@SiO_2 catalysts with different Ce/Cu mass ratios were synthesized by the two-step hydrothermal and incipient wetness impregnation methods,and characterized by multitechnique characterizations,such as SEM,TEM,XRD,H_2-TPR,XPS and N_2 adsorption-desorption techniques.It is found that the hollow shell is composed of CuO and SiO_2,and CeO_2 nanoparticles are coated on the surface of CuO@SiO_2 support.And the CeO_2/CuO@SiO_2 catalyst with the Ce/Cu mass ratios of 1:1 denoted as 1 CeO_2/CuO@SiO_2,which possesses a maximum amount of highly dispersed copper species and medium-sized CuO as well as the highest concentration of oxygen vacancies,exhibits the highest catalytic activity and widest full CO conversion window.The barrier effect of the SiO_2 shell effectively prevents the reduction of CuO species,which broadens temperature window of CO total conversion and enhances CO_2 selectivity above 155℃over the 1 CeO_2/CuO@SiO_2 catalyst in comparison with the CuO-CeO_2 and CeO_2-CuO catalysts.     

Modified-EISA synthesis of mesoporous high surface area CeO_2 and catalytic property for CO oxidation

Mesoporous CeO2 particles with high surface area were synthesized using a modified evaporation-induced self assembly(EISA) method which combined citric acid as complexing agent.As-prepared powder and further thermal treatment samples were characterized by X-ray diffraction(XRD),transmission electron microscopy(TEM),selected area electron diffraction(SAED),Fourier transform infrared spectrometer(FTIR),thermogravimetry and differential thermal analysis(TG-DTA),Brunauer-Emmett-Teller(BET) and Barrett-Joyner-Ha...     

Effect of CeO_2-ZrO_2 on Pt/C electrocatalysts for alcohols oxidation

The electrocatalytic activity and stability of Pt/C catalyst modified by using CeO_2-ZrO_2 mixed oxides for the alcohols electrochemical oxidation as probes were investigated. The catalyst samples were characterized by X-ray diffraction(XRD) and scanning electron microscopy(SEM). The electrochemical properties were measured by a three electrode system on electrochemical workstation(IVIUM). The results showed that the presence of CeO_2-ZrO_2 might be associated with the presence of Pt, which indicated that possibly there was synergistic effect between CeO_2-ZrO_2 and Pt nanoparticles. The electrocatalytic activity and stability of Pt-MO_x/C(M=Ce, Zr) for methanol and ethanol oxidation was better than that of Pt-CeO_2/C, which was attributed to that CeO_2-ZrO_2 composited oxides enhanced oxygen mobility and promoted oxygen storage capacity(OSC). Furthermore, the best performance was found when the molar ratio of CeO_2 to ZrO_2 was 2:1 for the oxidation of methanol and ethanol. The forward peak current density of Pt-MO_x/C(M=Ce, Zr, Ce:Zr=2:1) towards the methanol electrooxidation was about 3.8 times that of Pt-CeO_2/C. Pt-MO_x/C(M=Ce, Zr) appeared to be a promising and less expensive methanol oxidation anode catalyst.     

CuO-CeO2/Al2O3/FeCrAl monolithic catalysts prepared by in situ combustion synthesis method for preferential oxidation of carbon monoxide

This work described in situ combustion synthesis method for depositing CuO-CeO2 on the FeCrAl honeycomb supports.The in-fluence of the solution concentration and the role of the additive were studied and analyzed by scanning electron microscopy (SEM),X-ray diffractometer (XRD),and temperature programmed reduction (TPR) techniques.The results showed that 200 g/L of the active solution was the most appropriate concentration for preparing the monolithic catalysts,and the additives of praseodymium and lanthanum...     

CuO-CeOe/AleO3/FeCrAl monolithic catalysts prepared by in situ combustion synthesis method for preferential oxidation of carbon monoxide

This work described in situ combustion synthesis method for depositing CuO-CeO2 on the FeCrAl honeycomb supports.The in-fluence of the solution concentration and the role of the additive were studied and analyzed by scanning electron microscopy (SEM),X-ray diffractometer (XRD),and temperature programmed reduction (TPR) techniques.The results showed that 200 g/L of the active solution was the most appropriate concentration for preparing the monolithic catalysts,and the additives of praseodymium and lanthanum improved the adhesion stability of the monolithic catalysts.The addition of Pr did not greatly affect the catalytic performance,but CO could not be totally converted into CO2 after the addition of La into the CuO-CeO2/Al2O3/FeCrAl catalysts.     

Activity and deactivation behavior of Au/LaMnO3 catalysts for CO oxidation

Perovskite oxide LaMnO3 was prepared by sol-gel method and the nanosize Au/LaMnO3 catalyst was prepared by deposition-precipitation(DP) method in the paper.Characterization of the catalyst sample was made by X-ray diffractometer(XRD),atom absorption spectra(AAS) and X-ray photoelectron spectroscopy(XPS) instrumental methods.The activity,long-term stability and the reasons for deactivation of the gold catalyst in CO oxidation were investigated.The experiment results demonstrated that the Au/LaMnO3 catalyst e...     

Preferential Oxidation of CO in H2 over CuO／CeO2 Catalysts

Over the past few years, the design and researchon fuel cells have been made a great development. Avariety of fuel cells for different applications has beenunder development[1,2]: solid polymer fuel cells(SPFC), also know as proton exchange …     

Promotional effect of CO pretreatment on CuO/CeO2 catalyst for catalytic reduction of NO by CO

The CuO/CeO2 catalysts were investigated by means of X-ray diffraction(XRD),laser Raman spectroscopy(LRS),X-ray photoelectronic spectroscopy(XPS),temperature-programmed reduction(TPR),in situ Fourier transform infrared spectroscopy(FTIR) and NO+CO reaction.The results revealed that the low temperature(150 °C) catalytic performances were enhanced for CO pretreated samples.During CO pretreatment,the surface Cu+/Cu0 and oxygen vacancies on ceria surface were present.The low valence copper species activated the adsorbed CO and surface oxygen vacancies facilitated the NO dissociation.These effects in turn led to higher activities of CuO/CeO2 for NO reduction.The current study provided helpful understandings of active sites and reaction mechanism in NO+CO reaction.     

Promotional effect of CeO2 and Y2O3 on CuO/ZrO2 catalysts for methane combustion

Catalytic combustion of methane was conducted by using a Cu-based catalyst prepared by the plasma-assisted impregnation method. The properties of the catalysts were surveyed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and temperature-programmed reduction (H2-TPR). The results showed that the activity of CuO/ZrO2 with the CeO2 and Y2O3 was obviously increased compared with the CuO/ZrO2 catalyst, which was examined in relation to the structure and surface characteristics and might be correlated with their surface oxygen species and redox properties. Among the investigated catalysts, the Ce-CuO/ZrO2 sample exhibited the highest activity for methane combustion.     

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.     

Preparation, Characterization of CuO／CeO2 and Cu／CeO2 Catalysts and Their Applications in Low-Temperature CO Oxidation

CeO2 was synthesized via sol-gel process and used as supporter to prepare CuO/CeO2, Cu/CeO2 catalysts by impregnation method. The catalytic properties and characterization of CeO2, CuO/CeO2 and Cu/CeO2 catalysts were examined by means of a microreactor-GC system, HRTEM, XRD, TPR and XPS techniques. The results show that CuO has not catalytic activity and the activity of CeO2 is quite low for CO oxidation. However, the catalytic activity of CuO/CeO2 and Cu/CeO2 catalysts increases significantly. Furthermore, the activity of CuO/CeO2 is higher than that of Cu/CeO2 catalysts.     

Study on ceria-modified SnO2 for CO and CH4 oxidation

Sn-Ce-O binary catalysts with different Sn/Ce molar ratios were prepared with co-precipitation method and applied for CO and CH4 oxidation. The catalysts were characterized by means of N2-BET, XRD and H2-TPR techniques. It was found that for those Sn rich samples such as SnCe91 and SnCe73, Ce cations were doped into the matrix of tetragonal rutile SnO2 to form SnO2 -based solid solution. As a consequence, the oxidation activity as well as the thermal stability was significantly improved compared with pure SnO2 . In contrast, for Ce rich samples such as SnCe19, SnCe37 and SnCe55, though the thermal stability was improved, the activity was worse than SnO2,due to the presence of much less amount of active oxygen species. Co-precipitation was found to be the best method to prepare Sn-Ce binary catalysts among all of the methods tried in this study.     

New insights into the role of vanadia species as active sites for selective catalytic reduction of NO with ammonia over VO_x/CeO_2 catalysts

A series of VO_x/CeO_2 catalysts we re synthesized via vanadia supported on ceria with different BET surface areas.The catalysts were employed to investigate the active sites for the selective catalytic reduction of NO with NH_3(NH3-SCR).The kinetic results show that VO_x/CeO_2 catalysts exhibit nearly constant apparent activation energies(E_a),indicating the same SCR reaction mechanism.The V-O-Ce bridging modes and oligomeric VO_x were identified and quantified by Raman,FT-IR and H_2-TPR.The amounts of the V-O-Ce bridging modes calculated by H_2-TPR are correlated to the NH_3-SCR intrinsic reaction rates.The turnover frequencies(TOFs) show a constant value at the same temperature,which were calculated based on the number of V-O-Ce bridging modes of VO_x/CeO_2 catalysts.Therefore,it can be concluded that the V-O-Ce bridging modes are the active sites of VO_x/CeO_2 catalysts for the NH3-SCR reaction.