Origin of the High Activity of the Ceria-Supported Copper Catalyst for H₂O Dissociation

Ceria-supported copper is a wonderful catalyst for the water−gas shift (WGS) reaction which has been demonstrated experimentally. Using first-principles calculations based on density functional theory (DFT), we identify the mechanisms for the growth of small Cu clusters (Cux, x = 1−4) on ceria and the dissociation of H2O on the Cu4/CeO2 catalyst. Our calculations indicate that the strong copper−oxygen interaction at the Cu4/CeO2 interface is comparable to the copper−copper intracluster interactions, and the competitions between them determine the morphologies of Cu clusters on ceria. H2O dissociates with small barriers (0.19−0.31 eV) on the Cu4/CeO2 catalyst, and the highly catalytic activity originates from the enhanced electrostatic interaction between the positively charged Cu sites and the polar H2O molecule. The Cu/O interface sites of the ceria-supported copper catalyst are identified as the active sites for H2O dissociation. As a buffer to accept/release electrons, the ceria support not only activates the Cu sites but also participates in the H2O dissociation reaction at the Cu/O interface.