Identification of intrinsic active sites in ternary CuZnTi catalysts toward low-temperature water gas shift reaction

Abstract

In the heterogeneous field, modulation over strong metal-support interactions (SMSI) plays a crucial role in boosting catalytic performance toward interface-sensitive reactions (e.g., water gas shift reaction, WGSR). Herein, a CuZnTi ternary catalyst was prepared via in situ structural topological transformation from CuZnTi-layered double hydroxides precursor (CuZnTi-LDHs). The resulting catalyst Cu/ZnTi-MMO(H350) exhibits an extraordinarily high catalytic activity toward low temperature-WGSR with a reaction rate of 19.7 μmolCO gcat-1 s-1 at 250 °C, among the highest level in Cu-based catalysts. Advanced electron microscope and in situ spectroscopy characterizations verify that Cu nanoparticles (particle size: 7~10 nm) are modified by ZnTi-mixed metal oxides with abundant Cuδ+−Ov−Ti3+ (0<δ<1) interfacial sites. Incorporation of Ti element facilitates the reduction of ZnO to stabilize Cuδ+ species at the interface, which enhances the chemisorption of CO molecule. Simultaneously, neighboring Ov−Ti3+ species significantly promotes the dissociation of H2O molecule. The structure-activity correlation studies based on quasi-in situ XPS, in situ DRIFTS, in situ and operando EXAFS reveal that the interfacial sites (Cuδ+−Ov−Ti3+) serve as the intrinsic active sites of WGS reaction. A combination of in situ characterization techniques and DFT calculations further substantiate that associative mechanism is the predominant reactive path below 200 °C whilst redox mechanism is overwhelming above 250 °C in the presence of Cu/ZnTi-MMO catalyst. This work demonstrates a facile modulation on metal-support interfacial structure via LDHs approach, which paves a way for rational design and preparation of heterogeneous catalysts.