Structural Features of(Ce,La or Sr)(Mn or Co)O_3 NanoPerovskites as a Catalyst for Carbon Monoxide Oxidation

The collection of different cations in the A and B sites of ABO3 was explored for the regularity of perovskites phase formability.Here,Sr2？,La3？,and Ce4？are selected as the cations of site A.The site B is considered to be Mn or Co cations.XRD analysis and Fourier transform infrared spectroscopy results confirm the formation of perovskite structure for catalysts in which La3？and Sr2？are considered as the cations of site A.Ceria is detected as the main crystalline phase when Ce4？is selected to be cation of site A.It is found that the octahedral factor（rB/rO） takes the same important role as the tolerance factor to form cubic perovskite.Average crystallite size of the products was calculated by data of the XRD and measured by the TEM analysis.Results of the XRD and TEM studies were supported by the study of the particles size distribution,which was carried out in a particle size analyzer.The perovskite samples were also used for stoichiometric oxidation of carbon monoxide with air.

Preparation, Characterization of CuO/CeO_2 and Cu/CeO_2 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.

Low-temperature CO oxidation over CuO-CeO_2/SiO_2 catalysts:Effect of CeO_2 content and carrier porosity

The effects of CeO2 contents and silica carrier porosity with their pore diameters ranging from 5.2 nm to 12.5 nm of CuO-CeO2/SiO2 cata-lysts in CO oxidation were investigated.The catalysts were characterized by N2 adsorption/desorption at low temperature,X-ray diffraction （XRD）,temperature-programmed reduction by H2 （H2-TPR）,oxygen temperature programmed desorption （O2-TPD） and X-ray photoelectron spectroscopy （XPS）.The results suggested that,the ceria content and the porosity of SiO2 carrier possessed great impacts on the structures and catalytic performances of CuO-CeO2/SiO2 catalysts.When appropriate content of CeO2 （Ce content 8 wt%） was added,the catalytic activity was greatly enhanced.In the catalyst supported on silica carrier with larger pore diameter,higher dispersion of CuO was observed,better agglomeration-resistant capacity was displayed and more lattice oxygen could be found,thus the CuO-CeO2 supported on Si-1 showed higher catalytic activity for low-temperature CO oxidation.

Optimization and statistical analysis of Au-ZnO/Al_2O_3 catalyst for CO oxidation

In our former work [Catal. Today 174 （2011） 127], 12 heterogeneous catalysts were screened for CO oxidation, and Au-ZnO/Al2O3 was chosen and optimized in terms of weight loadings of Au and ZnO. The present study follows on to consider the impact of process parameters （catalyst preparation and reaction conditions）, in conjunction with catalyst composition （weight loadings of Au and ZnO, and the total weight of the catalyst）, as the optimization of the process parameters simultaneously optimized the catalyst composition. The optimization target is the reactivity of this important reaction. These factors were first optimized using response surface methodology （RSM） with 25 experiments, to obtain the optimum： 100 mg of 1.0%Au-4.1%ZnO/Al2O3 catalyst with 220℃ calcination and 100℃ reduction. After optimization, the main effects and interactions of these five factors were studied using statistical sensitivity analysis （SA）. Certain observations from SA were verified by reaction mechanism, reactivity test and/or characterization techniques, while others need further investigation.

Catalytic Activity of Ceria-Zirconia Nanostructured Materials Prepared via Reversed Microemulsion Method

Single-phase homogeneous Ce1-x ZrxO2 solid versed microemulsion method. The structural properties solutions with various compositions were synthesized using the reand performance of Ce1- xZrxO2 were studied using XRD, BET, SEM, HRTEM, TPR and CO oxidation measurements. The results show that in the range of x = 0.4 - 0.5 and x = 0.6 - 1.0, the solid solutions posses the cubic and the tetragonal phase structure, respectively, Solids obtained by the reversed microemulsion method were more homogeneous on the whole range of composition, XRD investigations of the prepared materials did not show segregation of cerium or zirconium oxides, Highly uniform nanosize solid solution particles of ceria-zirconia with high specific area （146.7 m^2·g^-1） were attained under the conditions of this study. The TPR results and CO oxidation measurements indicate that the performance of the CeO2-ZrO2 mixed oxides is strongly related to the composition and structure of the oxides. Enhancement of the activity was found for the catalyst prepared by reversed microemulsion method as compared to the sample prepared by sol-gel method.

Electrical,Magnetic and Catalytic Investigations on Some Manganite Perovskites Prepared by Combustion Method

AMnO3 （A=Sr, Sm and Nd） manganites with perovskite structure, prepared by combustion method were characterized by X-ray diffraction （XRD）, infra-red spectroscopy, Brunauer-Emmett-Teller （BET） surface area analyzer and scanning electron microscopy （SEM）. The solid state and spectroscopic studies such as electrical resistivity, magnetic susceptibility, electron spin resonance （ESR） and diffuse reflectance spectroscopy were carried out and attempted to correlate with the catalytic activities of the compounds. To evaluate the catalytic activity, a model reaction of CO oxidation over these compounds was undertaken. An attempt was made to understand the effect of A-site change by different metal cations in the manganite perovskites on solid state and catalytic properties.