(139b) Theoretical Investigation of the Water-Gas Shift Reaction at the Three-Phase Boundary of TiO2 Supported Metal Clusters

Precious metal nanoparticles supported on reducible oxides are known to exhibit excellent activity and selectivity for the water-gas shift reaction (WGSR) which is a key step in fuel processing to maximize hydrogen yield and for providing clean hydrogen. In this paper, we investigate the reaction mechanism of the WGSR at the three-phase boundary (TPB) of a gas-phase, a TiO2 support, and Au and Pt clusters using periodic slab and periodic electrostatic embedded cluster models. The primary objective of our investigation is understanding the importance of the TPB for the WGSR and to develop and validate a highly efficient and accurate computational strategy for these systems. We used both hybrid and non-hybrid density functional methods on the embedded cluster models to calculate the reaction enthalpies and activation barriers for the key reaction steps that involve oxygen vacancies and hydroxyl species. A proper description of the electronic structure of these systems could only be obtained by using hybrid density functionals. Finally, we also studied the effect of Hartree-Fock exchange on the description of the strength of chemical bonds in defective oxide surfaces.