Au^δ−–O_v–Ti³⁺ Interfacial Site: Catalytic Active Center toward Low-Temperature Water Gas Shift Reaction

Abstract

The electronic metal–support interaction (EMSI) plays a crucial role in promoting catalytic performance toward interface electronic structure sensitive reactions, such as the low temperature water gas shift reaction (LT-WGSR). Herein, a mixed metal oxide support (ZnTi-MMO) was obtained via structural topological transformation from a zinc–titanium layered double hydroxides (ZnTi-LDHs) precursor, which was used for the immobilization of Au nanoparticles (NPs). Following a reduction pretreatment at 300 °C in a H2 atmosphere, the resulting optimal catalyst Au@TiO2–x/ZnO(H300) exhibits a WGSR rate up to 0.15 molco molAu–1 s–1, which is at a high level compared with previously reported gold-based catalyst systems. Ac-HAADF-STEM combined with CO pulse chemisorption measurements verifies a TiO2–x overlayer on the surface of Au NPs. Quasi in situ XPS, EPR, in situ EXAFS, and in situ DRIFTS demonstrate the formation of interface dual-active-site (Auδ−–Ov–Ti3+; Ov: oxygen vacancy) based on electron transfer from the TiO2–x overlayer to Au atoms, in which the electron-enriched Auδ− species enhance CO chemisorption while Ov–Ti3+ accelerates the dissociation of the H2O molecule, accounting for the largely enhanced catalytic activity and stability of Au@TiO2–x/ZnO(H300) compared with the traditional Au/TiO2 system. In situ/operando EXAFS further confirms that Auδ−–Ov–Ti3+ interfacial site serves as the optimal active site toward WGSR: both Auδ− species and Ov directly participate in the rate-determining step of LT-WGSR (water dissociation). The discovery and identification of the interfacial active site in this system can be extended to other metal catalysts with largely promoted performance in heterogeneous catalysis.