Synthesis of polyoxometalate encapsulated in UiO-66(Zr) with hierarchical porosity and double active sites for oxidation desulfurization of fuel oil at room temperature

Abstract

Catalytic oxidative desulfurization (ODS) of fuel oil has received much attention. For this, the synthesis of a highly efficient ODS catalyst has been strongly pursued. Polyoxometalates (POMs) as active centers have been studied for ODS reactions. However, generally the obtained POM catalysts exhibited ordinary catalytic ODS performance mainly due to the role of single active sites. Moreover, the synthesis needs to be completed with the addition of solvent. In this work, we report a new approach to prepare highly efficient ODS catalysts with POM sites. This process can be simply realized by the combination of a common POM (H₃PW₁₂O₄₀) and a stable metal–organic framework (MOF) material UiO-66(Zr) without the addition of solvent. More importantly, it is found that polyoxometalate encapsulated in UiO-66(Zr) possesses hierarchical porosity and double active sites. As a result, the catalyst exhibited extraordinary catalytic activity by using H₂O₂ as an oxidant in the ODS reactions of benzothiophene, dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene. The turnover frequency (TOF) for the removal of DBT reached 293 h⁻¹ at room temperature, which is much higher than that of the reported catalysts. Such outstanding catalytic performance could be mainly attributed to easy accessibility of active sites and the existence of two types of active centers in polyoxometalate species and defective UiO-66(Zr).