Oxygen Species and Their Reactivity in the Mechanochemically Prepared Substituted Perovskites La1-xSrxCoO3-y
(x = 0–1)
Kinetics and Catalysis
, E-ISSN: 1608-3210
Boreskov Institute of Catalysis SB RAS
The oxygen species and their reactivity in the mechanochemically prepared substituted perovskites La1−x SrxCoO3−y were studied using temperature-programmed reduction (TPR) of the samples with hydrogen. The experimental data were compared with data on the catalytic activity of the series of La1−xSrxCoO3−y catalysts in the oxidation of CO, as well as with the real structures and surface compositions of the samples, which were studied in detail previously. As the strontium content was increased, the degree of reduction of the samples increased in the course of TPR and the TPR peaks shifted to the region of lower temperatures, except for the last sample containing no lanthanum (x = 1). An increase in the calcination temperature and time resulted in a decrease in TPR peak intensities and in a shift of the peaks to the region of higher temperatures. A reaction scheme was proposed for the reduction. In accordance with this reaction scheme, Co4+ in substituted cobaltites was reduced to Co0 at temperatures lower than 400°C. In the temperature region of 400–500°C, the Co3+ → Co2+ bulk reduction, as well as the deep reduction processes Co3+ → Co0 and Co4+ → Co0, occurred; substitution facilitated the above processes. At temperatures higher than 500°C, Co2+ → Co0 bulk reduction occurred. The observed reduction of the mechanochemically prepared samples depended on their microstructure, which was described previously. It was found that the activity of the samples in the oxidation of CO depends on the amount of the most weakly bound reactive surface oxygen species, which were removed in TPR with hydrogen to 150°C. No correlation between the amount of strongly bound (lattice) oxygen removed upon TPR and the activity of La1−xSrxCoO3−y samples in the oxidation of CO was found.