Oxidative catalytic versatility of a trivacant polyoxotungstate incorporated into MIL-101(Cr)

Abstract

The first immobilization of the trivacant Keggin-type polyoxometalate ([A-PW₉O₃₄]⁹⁻, PW₉) to prepare a novel heterogeneous oxidative catalyst is here reported. PW₉ was incorporated into the cavities of the chromium terephthalate metal–organic framework MIL-101(Cr). Characterization of the composite PW₉@MIL-101 by powder X-ray diffraction, SEM-EDX, FT-IR, FT-Raman spectroscopy, N₂ adsorption–desorption isotherms and ³¹P solid-state NMR confirmed that the structures of MIL-101 and the polyoxometalate anion were retained after immobilization. The composite PW₉@MIL-101 revealed versatility as a heterogeneous catalyst to oxidize efficiently monoterpenes as well as to reach a complete desulfurization of a model oil containing the most refractory sulfur compounds in fuel, using in both systems acetonitrile as the solvent and H₂O₂ as the oxidant. Complete conversion of geraniol to 2,3-epoxygeraniol was achieved after the first 30 min at room temperature, while the total desulfurization of the model oil containing 1707 ppm of sulfur was attained after 2 h. In both systems the catalyst was recyclable for various cycles without a significant loss of activity. The stability and heterogeneity of the catalyst were confirmed by several techniques and by leaching tests.