Computational Screening of Pt@TiCT (T = O, S) MXene Catalysts for Water-Gas Shift Reaction.

Single-atom catalysts (SACs) provide an opportunity to elucidate the catalytic mechanism of complex reactions in heterogeneous catalysis. The low-temperature water-gas shift (WGS) reaction is an important industrial technology to obtain high purity hydrogen. Herein, we study the catalytic activity of Pt@TiCT (T = O, S) SACs, where one subsurface Ti atom with three T vacancies in the functionalized TiCT (T = O, S) MXene is substituted by one Pt atom, for the low-temperature WGS reaction, using density functional theory (DFT). The results show that Pt@TiCT provides an excellent platform for the WGS reaction by its bowl-shaped vacancy derived from the Pt single atom and three T defects surrounding it. Especially, Pt@TiCS SAC has higher catalytic performance for the WGS reaction, due to the weaker electronegativity of the S atom than the O atom, which significantly reduces the energy barrier of H* migration in the WGS reaction, which is often the rate-determining step. In the most favorable redox mechanism of the WGS reaction on Pt@TiCS, the rate-determining step is the dissociation of OH* into O* and H* with the energy barrier as low as 1.12 eV. These results demonstrate that Pt@TiCS is promising in the application of MXenes for low-temperature WGS reactions.