La_(1-x)Ca_xCoO_3 perovskite-type oxides:preparation,characterisation,stability,and catalytic potentiality for the total oxidation of propane

摘要

La_(1-x)Ca_xCoO_3(x=0,0.2,0.4,0.5)perovskite-type oxides were prepared by the citrate method and characterised by different techniques.Thermogravimetry,X-ray diffraction(XRD),and specific surface area results were used to choose the best synthesis conditions.From the XRD results,the crystalline structure was refined with the Rietveld method.Substitution of Ca for La does not modify the preparation process of the perovskites but changes the crystalline structure slightly.An excess of lanthanum was detected by inductively coupled plasma spectroscopy,which would be at the surface as an oxide susceptible to carbonation.The reactivities of the different oxygen species were studied from the results of temperature-programmed desorption of oxygen and temperature-programmed reduction.The catalytic potential was tested in propane total oxidation.The close parallel between the catalytic activity and the oxygen species amount adsorbed on the surface oxygen vacancies indicates that the propane oxidation on La_(1-x)Ca_xCoO_3 catalysts proceeds through a suprafacial reaction mechanism.