Catalytic activity and sulfur tolerance for Mn-substituted La0.75Sr0.25CrO3±δ in gas containing H2S

Abstract

Lanthanum chromites substituted by transition metal are potentially applied as anode catalysts in solid oxide fuel cell fed with fuel gas containing H2S. In order to understand the effect of composition on catalytic activity and sulfur tolerance of anode catalysts, La0.75Sr0.25Cr1−xMnxO3±δ (noted as LSCM, x = 0.2, 0.5, 0.8) series were synthesized and characterized by XRD, XPS and H2-TPR. The results demonstrate that LSCM55 with moderate Mn-substitution content has the highest activity for H2S, which is attributed to considerable reducibility of Mn4+ determined by H2-TPR. XRD patterns reveal that as-synthesized samples with different Mn-substitution contents have different sulfur tolerance. Sr 3d5/2, Cr 2p3/2, Mn 2p3/2 regions of XPS for samples with different Mn-substitution contents imply that dominance of Mn4+, responsible for the catalytic activity, is the consequence of the interactions between cations at A-site and B-site. On the other hand, evolution of Mn in H2S atmosphere indicates Mn3+ in Mn4+-O-Mn3+ clusters contributes greatly to the sulfur tolerance of LSCM. By analyzing consistency in the contents of lattice oxygen, S species (mainly sulfate) and Mn3+, a hypothetical mechanism of LSCM catalysts involving catalysis and sulfur tolerance was proposed.