Zirconia-Supported MoOx Catalysts for the Selective Oxidation of Dimethyl Ether to Formaldehyde: Structure, Redox Properties, and Reaction Pathways

摘要: Dimethyl ether (DME) reacts to form formaldehyde with high selectivity at 500−600 K on MoOx−ZrO2 catalysts a wide range of MoOx surface density (0.5−50.1 Mo/nm2) and local structure (monomers, oligomers, MoO3 crystallites, ZrMo2O8). Reaction rates (per Mo-atom) increased markedly as from 2.2 6.4 Mo/nm2 two-dimensional polymolybdates clusters became the prevalent active species. The rate incipient stoichiometric reduction samples in H2 also increasing density, suggesting that catalytic turnovers involve redox cycles become faster size dimensionality domains increase. DME reaction decreased densities above Mo/nm2, ZrMo2O8 increasingly inaccessible species form. On ZrMo2O8, areal reach constant value 10 exposed surfaces covered ...