Oxygen and Electron Storage Effects in W-Modified Ceria Catalysts for Ammonia Conversion

Tungsten-modified CeO₂ is an excellent catalyst for the catalytic conversion of ammonia. However, the geometric and electronic properties of this catalyst and the detailed reaction mechanisms are not well understood. In this work, the potential configurations of various monomer tungsten oxides supported on the CeO₂(111) surface (WO_X(x = 0-4)/CeO₂(111)) are systematically studied and their relative stabilities are evaluated by using on-site Coulomb interaction corrected density functional theory calculations. Their performances are also investigated in enhancing the catalytic efficiency of NH₃ adsorption and activation. It is found that the WO_x clusters can always form tetrahedron-like structures on the CeO₂(111) surface, and the CeO₂(111) can exhibit both oxygen- and electron-storage roles to help the WO_X maintain such tetrahedron-like WO₄ structures and keep the W species at the highest 6+ state. Moreover, the flexibility of the tetrahedral WO₄ structure leads to the preferential heterolytic NH₃ dissociation at the WO sites, forming stable WNH₂ and OH species. This study deepens the understanding of the unique oxygen- and electron-storage effects of the CeO₂ support, it also provides valuable insights into the extraordinary catalytic properties of the W-modified CeO₂ in NH₃ conversion, paving the way for the rational design of more efficient CeO₂-based NH₃ treatment catalysts.