The distinct effects of substitution and deposition of Ag in perovskite LaCoO3 on the thermally catalytic oxidation of toluene

Noble metal modification is one of efficient ways to improve the catalytic activity of perovskite-type catalysts towards VOC oxidation. However, precisely how the occurrence of noble metals in perovskite, i.e., substitution and deposition constrain the catalytic activity remains controversial. In this study, Ag substituted LaCoO3 perovskite (La1-xAgxCoO3) and LaCoO3 supported Ag (Ag/LCO) catalysts were synthesized by the one-pot method and impregnation, respectively, followed by the characterization of XRD, XPS, HRTEM, O-2-TPD, H-2-TPR, and periodic steady-state catalytic oxidation of toluene. In the La1-xAgxCoO3 series, Ag+ was incorporated in structure at the low substitution level, but at high substitution level, partial Ag+ diffused to the surface and was reduced as Ag-0. Among Ag/LCO catalysts, different microstructures of Ag, i.e., surface Ag2O, surface Ag-0, and both surface Ag-0 and substituted Ag+ were obtained under calcinations at 250, 450 and 700 degrees C, respectively. The catalytic activity of above catalysts was compared in terms of the temperatures for toluene conversions of 50% (T-50), 90% (T-90), and specific reaction rate (Rs). The catalytic activity of La1-xAgxCoO3 was enhanced with Ag content, but was lower than the Ag/LCO catalysts with identical Ag content. The activity of Ag/LCO increased in the following sequence: LaCoO3 < Ag/LCO-450 < Ag/LCO-700 < Ag/LCO-250. The distinct effect of Ag substitution and deposition on the catalytic activity of LaCoO3 was ascribed to the different surface oxygen composition and reducibility, and the interaction between Ag/Ag2O and LaCoO3 support.