Activity in methane combustion and sensitivity to sulfur poisoning of La1−xCexMn1−yCoyO3 perovskite oxides

Abstract

The activity in methane combustion and sensitivity to sulfur poisoning of a series of perovskite type oxides La1−xCexMn1−yCoyO3 (x=0, 0.1, 0.2, 0.3 and y=0.3, 0.5, 0.7), prepared by the citrate method were investigated. The citrate method and calcination 5h at 973K gave homogeneous oxides exhibiting the XRD pattern typical of perovskite structure, with traces of ceria when x≥0.1. Specific surface areas were from 10 to 31m2/g, depending on composition. In general, these catalysts were less active than the La1−xCexCoO3 and La1−xCexMnO3 compositions with x=0–0.5, except LaCoO3. No gain in performance was observed by mutual Co and Mn B-site substitution. As expected, all these catalysts are sensitive to sulfur dioxide (or H2S) in the feed, but the rate of poisoning varies significantly with composition. A low degree of substitution by cerium seems to slow the poisoning process. La0.9Ce0.1CoO3, La0.8Ce0.2CoO3 and La0.8Ce0.2MnO3 compositions were the least sensitive. After 15h exposure at 823K to 20ppm SO2 added to the feed, conversion of 1% methane to CO2 remained more than 80% of the original. XPS analysis of spent samples showed the presence of surface S6+ species, even when no bulk sulfate formation was detected by XRD. However, XRD analysis of samples exposed 40h to 80ppm SO2 (or H2S) indicates partial catalyst decomposition with the formation of La2(SO4)3, CeO2 and Co3O4.