Synthesis, crystal structure and catalytic activity for C 3H 6 combustion of La–Sr–Cu–O–S with K 2NiF 4-type perovskite structure

Abstract

K 2NiF 4 perovskite-type oxide catalysts containing sulfur, La 2− x Sr x CuO 4S y ( 0 ⩽ x ⩽ 0.3 ; 0 ⩽ y ⩽ 0.3 ), were synthesized to study their crystal structure, reduction–oxidation property, and catalytic activity for the combustion of C 3H 6 in the presence of SO 2. Results of XRD, Rietveld analysis, TG, and XPS demonstrated that sulfur is located in the interstitial site between perovskite slabs as nonsulfate species (S 4+/S 6+). Because of the high positive valence of sulfur in the lattice, resulting charge compensation decreased the oxidation number of Cu from 2.08 ( y = 0 ) to 1.86 ( y = 0.2 ), accompanied by the creation of more reducible Cu species in TPR profiles, which would achieve the light-off of catalytic C 3H 6 combustion at lower temperatures. Admission of SO 2 into the feedstream caused either a negative or a positive effect on the catalytic C 3H 6 oxidation, depending on the concentrations of SO 2 and O 2. More significantly, however, activation in the presence of SO 2 was observed for sulfur-containing compound ( y = 0.2 ), which suppressed the accumulation of adsorbed SO 2 as sulfate ( SO 4 2 − ). It is proposed that the adsorption of SO 2 leads to either positive or negative effects on catalytic activity depending on the oxidation state. The sulfur-containing compounds on exposure to SO 2 would create the surface active site effective for the adsorption and combustion of C 3H 6.