Titania crystal-plane-determined activity of copper cluster in water-gas shift reaction

Abstract

It is critical to probe the effect of the crystal plane of TiO2 support on the water-gas shift reaction (WGSR). Density functional theory (DFT) and microkinetic modeling were performed to investigate the reaction mechanism and reaction kinetics of WGSR on copper cluster on Anatatse-TiO2(001), TiO2(100), TiO2(101) surfaces. The calculation results indicated that three TiO2-supported Cu catalysts mainly carry out carboxyl pathway and redox pathway because the hydroxyl and oxygen species can be largely stabilized, and the TiO2(001) supported copper cluster exhibits the best catalytic performance for WGSR compared with other crystal plane. Compared with the d-band center of Cu(111), the strong interaction between the copper cluster and TiO2 support exposed (001) and (100) crystal planes can make the d-band center of the upper atoms of copper cluster shift upward and the lower Cu atoms shift downward, which in turn leads to the strong adsorption strength of reactants and oxygenates, and further the catalytic performance of WGSR has been significantly improved. The essential reason for crystal plane effect of TiO2 on WGSR is the difference in the surface energy and the surface geometry. Specifically, the higher the surface energy of TiO2 reflected by the high concentration of unsaturated two-coordinate oxygen(O2c), which enhanced Cu-TiO2 interaction, and ultimately the better the catalytic performance of TiO2 crystal plane. This work not only reveals the effect of TiO2 crystal plane in WGSR, but also provides reliable guidance for its application in other catalysis fields.