Calcium and strontium substituted lanthanum manganite–cobaltite [La1−x(Ca,Sr)xMn0.5Co0.5O3] nano-catalysts for low temperature CO oxidation

Abstract

In this work, structural and catalytic properties of La1−xCaxMn0.5Co0.5O3 and La1−xSrxMn0.5Co0.5O3 nano-catalysts in the concentration range of 0.00≤x≤1.00 are investigated. The structural characterization of the compounds obtained by X-ray powder diffraction and using X′Pert package and Fullprof program is an evidence for structural phase transition of the samples that can be described by variation of tolerance factor. The obtained results also have been confirmed by FTIR measurements. The structural results, and the non-uniformly changes of activation energy, band gap energy and electrical conductivity values suggest the presence of different concentration of various cations Co+2, Co+3, Co+4, Mn+4 and Mn+3 in the compounds studied. The decrease of the crystallite size with increasing Ca and Sr substitution for x up to 0.5 in La1−x(Sr, Ca)xMn0.5Co0.5O3 can be related to the increase and decrease of micro-strain, respectively. Substituting Sr having higher ionic radius with respect to La in LaMn0.5Co0.5O3 shifts the catalytic activity of CO oxidation to lower temperature, whereas, for Ca substitution the catalytic activity shifts to higher temperature. The trend of catalytic activity observed for Ca- and Sr-substituted samples can be related to different morphology observed in SEM micrographs due to different types of micro-strain. La0.5Sr0.5Mn0.5Co0.5O3 nano-catalyst exhibits excellent CO conversion rate of 95% at 175°C.