Alternative ball-milling synthesis of vanadium-substituted polyoxometalates as catalysts for the aerobic cleavage of C–C and C–O bonds

Abstract

Vanadium-substituted phosphomolybdic acids (H_3+x[PMo_12−xV_xO₄₀], denoted as V_x) are well-known oxidation catalysts that are generally prepared by the hydrothermal treatment of MoO₃ and V₂O₅ in the presence of H₃PO₄. This synthesis procedure is highly energy consuming and the V_x yields are not always acceptable. In the present work, an alternative hybrid mechanochemical/hydrothermal synthesis of V_x is proposed, comprising the ball-milling of MoO₃ and V₂O₅, followed by a hydrothermal attack. The resulting materials, with 2 ≤ x ≤ 3, obtained from this new route were compared, in terms of yield, energy consumption and catalytic activity, with a reference V₃ sample prepared through a conventional hydrothermal treatment. The ball-milling step proved to lead not only to a shorter and far more energy-saving synthesis procedure, but also to high yields of V_x. Moreover, V_x from this alternative route proved to be generally more active than the conventionally prepared V₃ in the aerobic oxidative cleavage of C–O and C–C bonds in 2-phenoxyacetophenone, used herein as a lignin model compound.