La–Mn perovskite-type oxide prepared by combustion method: Catalytic activity in ethanol oxidation

Abstract

The present work deals with the use of the combustion method to synthesize a series of lanthanum manganite (LM) and to study their physico-chemical and catalytic properties in ethanol deep oxidation. Some synthesis parameters such as chemical nature of the fuel molecules (glycine and citric acid) and additional thermal treatment were used and their effects on the powder characteristics were studied. XRD patterns showed a single phase perovskite-type oxide for all studied samples. Additional lanthanum oxocarbonate was observed on powder patterns of samples obtained with citric acid. The presence of chemisorbed carbonate species was studied by IR spectra analysis in the 2000–500 cm −1, XRD and XPS analyses of the C1s and O1s levels. Their concentration was higher on surface samples prepared with citric acid than on those prepared with glycine. From XPS results, the use of glycine as gelling agent rather than citric acid and additional thermal treatment resulted in a decrease in superficial La/Mn atomic ratio and carbonate content and in an increase in relative content of the surface O 2 2−/O − species. These preparation parameters determined the best catalytic activity of the studied LM materials. Our results indicated that the catalytic activity in deep oxidation of ethanol over lanthanum manganite may be described as a synergetic effect of lanthanum and manganese. Ethanol activation was favoured by the strong basicity of lanthanum oxide at the surface of perovskite-structure and deep oxidation to CO 2 was enhanced by the activation of oxygen species on manganese site through a redox cycle.