A DFT plus U study about agglomeration of Au atoms on reduced surface of rutile TiO2 (110)

The sintering deactivates CO oxidation in a single Au catalyst. Understanding the mechanism of sintering at a reduced atmosphere seems important for improving sintering resistance. Here, we employ the first principle calculations to evaluate the barrier energy of Au atoms on reduced rutile TiO2 (110) surface and to demonstrate a favorable channel for their diffusion at an early stage in sintering. In the current DFT + U calculations, 16 structural configurations with oxygen vacancies and Au atoms are considered. This shows that Au atoms prefer to mobilize on fivefold-coordinated Ti (Ti5c) row rather than moving perpendicularly from this Ti5c row to a twofold-coordinated O (O2c) row. We regard a trap center involving a complex of Au-oxygen vacancy on an O2c row as the initial nucleation site during sintering. It will capture the unstable Au atom on a Ti5c row, and hence, a highly stable Au dimer would be produced as the primary nucleation pattern.