A Temperature-Programmed-Reduction Study on La1−xSrxCrO3 and Surface-Ruthenium-Modified La1−xSrxCrO3

Abstract

A series of La1−xSrxCrO3(0⩽x⩽0.3) composite oxides were prepared by a modified citric method. These perovskite oxides were further modified with Ru through impregnation. X-ray diffraction, X-ray photoelectron spectroscopy (XPS) and temperature-programmed-reduction (TPR) techniques were adopted to investigate the properties of both the as-prepared perovskite oxides and the surface-Ru-modified La1−xSrxCrO3 samples. XPS results indicated the existence of Cr6+ ions in the fresh samples and transformed to Cr3+ after reduction. The hydrogen consumed by these perovskite oxides during TPR increased with the Sr doping, which was more than twice of the theoretical value according to Kröger-Vink notation. The reduction temperature of Cr ions of Ru∕La1−xSrxCrO3 significantly decreased with an increase of the Ru loading. A small reduction peak at ∼540°C, which was not shifted by increasing Ru loadings, was observed and could be ascribed to the reduction of trace chromate phases. On all TPR profiles of the three doped perovskites with unity of the A-site and B-site ratio, the reduction of Ru species could not be observed at low Ru loadings (0.05% and 0.1%). A reduction peak from RuO2 particles appeared at temperatures prior to the perovskite reduction on the TPR plots of modified La0.9Sr0.1CrO3 and La0.8Sr0.2CrO3 with high Ru loading (0.5% and 1%, respectively), but it did not occur with the Ru modified La0.7Sr0.3CrO3 in the investigated Ru loading range. The TPR results of the Ru modified La0.8Sr0.2Cr0.95O3 depicted that some Ru ions might be stabilized due to the incorporation into the oxide.