Peroxomolybdate@MOFs as effective catalysts for oxidative desulfurization of fuels: correlation between MOF structure and catalytic activity

Abstract

The highly active peroxomolybdate, TBA₃{PO₄[MoO(O₂)₂]₄}·3H₂O (abbreviated as PMo₄), was incorporated for the first time in various porous MOF support structures (MIL-101, MOF-808, and ZIF-8) to form heterogeneous catalysts with different structural properties. These catalysts were used to treat a multicomponent model diesel via an oxidative desulfurization process. Sulfur-free diesel could be obtained after only 2 h depending on the porous MOF structural morphology. The size of the window entrance and the dimension of the pore from the MOF support had a remarkable influence on the catalytic performance of PMo₄@MOF catalysts, and thus, the conditioning of reactant diffusion. PMo₄@MIL-101 presented the highest catalytic efficiency (100% after 2 h), followed by PMo₄@MOF-808 (73.1% at 2 h) and PMo₄@ZIF-8 (68.1% at 2 h). Furthermore, the most active catalyst, PMo₄@MIL-101, showed remarkable recycle capacity and structural stability (maintaining the activity and stability for 10 catalytic cycles). Appropriate window and pore size cavities from MIL-101 support were the most suitable for organosulfur oxidation. Smaller windows and pore sizes from the other MOFs caused a decrease in catalytic efficiency. The windows and porous dimensions from MOF-based catalysts have a direct effect on catalyst performance, and these must be adjusted to reactants and active guest centers to avoid leaching and allow a fluent diffusion of reactants, mainly the ones with large molecular sizes.