Identification of the Active Cu Phase in the Water-Gas Shift Reaction over Cu/ZrO2 from First Principles

The water-gas shift (WGS) reaction (H2O + CO f H2 + CO2) is regarded as a key catalytic process in a future hydrogen economy. In this report, first-principles density functional theory (DFT) calculations have been utilized to identify the WGS mechanism over a Cu/oxide model catalyst, Cu/ZrO2. The catalytic reaction is found to occur at the Cu sites that are in the vicinity of Cu/oxides interfaces, where the Cu electronic structure is markedly modified by the oxygen-rich Cu/oxides interface. DFT-based microkinetic modeling further shows that a COOH-involved mechanism is responsible for the WGS reaction, with the H2O dissociation step being rate-controlling. By comparing the reaction thermodynamics and kinetics over three systems, namely, Cu/ZrO2, unsupported Cu strip, and Cu(111), we demonstrate that positively charged Cu clusters afford much enhanced catalytic activity in H2O dissociation. The ZrO2 support acts as a charge buffer to accept/release electrons from/to the Cu particle. The oxygen-rich metal-oxide interface, although not directly involved in catalysis, acts as a key promoter in enhancing catalytic activity in Cu-based catalysis. 1