Unraveling the Origin of Ceria Activity in Water-Gas Shift by First-Principles Microkinetic Modeling

Water-gas shift (WGS) is a well-known reaction for production and purification of hydrogen from synthesis gas. Transition metals supported on ceria (CeO2) have received much attention as single-step catalysts for the low-temperature WGS reaction. The intrinsic WGS activity of the ceria support indicates that it might play an essential role in the catalytic process. However, there is still no consensus on the governing reaction mechanism at mild conditions. Thus, in this work self-consistent periodic density functional theory and microkinetic calculations were performed to investigate redox, formate-mediated, and carboxyl-mediated pathways on the CeO2 (111) surface. Binding energies of reactants (H2O and CO), intermediates (OH, formate, and carboxyl), and products (CO2 and H-2) were calculated, together with energy barriers associated with possible elementary reaction steps. These results were used as input in a mean-field microkinetic model. The analysis of degrees of rate control from microkinetic calculations shows the prevalence of a combined redox-associative route for WGS on pure ceria. Overall, these results provide insight into the WGS reaction on ceria and can contribute to experimental research of catalytic systems for low-temperature WGS.