Enhanced CO catalytic oxidation by Sr reconstruction on the surface of La_xSr_1-xCoO_3-δ

Surface electronic structure of solid materials plays a critical role in heterogeneous catalysis. However, surface chemical composition of the perovskite oxides is usually dominated by segregated A-site cations and the amount of oxygen vacancies is relatively low, which seriously restricts their catalytic oxidation property. Here, we prepare perovskite La_xSr_1-xCoO_3-δ (x=0.3, 0.5, 0.7) with different Sr doping amount and experiment results show that perovskite LSCO with higher content of surface Sr possesses more oxygen vacancies and better catalytic activity. On this basis, we develop a new experimental strategy to create more surface oxygen vacancies to promote their CO catalytic activity. In this method, we use high active hydrogen atoms (BH^4-) as reductant to realize surface in-situ chemical composite modification of La_xSr_1-xCoO_3-δ (x=0.3, 0.5, 0.7), which causes their surface reconstruction (surface Sr enrichment). The regulation mainly focuses on the atomic layer level without damaging their bulk phase structure. Different from traditional high temperature annealing under reducing atmosphere, this method is high-efficiency, green and controllable. Furthermore, we study the surface reconstruction process and demonstrated that it is atomic layer engineering on the surface of La_xSr_1-xCoO_3-δ (x=0.3, 0.5, 0.7) by X-ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure (XAFS). Our experiment results also show that these samples treated by this method exhibit superior activity for CO oxidation compared with original samples.