Crystalline Mo [sbnd]V [sbnd]O based complex oxides as selective oxidation catalysts of propane

Abstract

Three single crystalline Mo V O based oxides, Mo V O, Mo V Te O and Mo V Te Nb O, all of which have the same orthorhombic layer-type structure with the particular arrangement of MO 6 (M = Mo, V, Nb) octahedra forming slabs with pentagonal, hexagonal, and heptagonal rings in (1 0 0) plane, were synthesized by hydrothermal method and their catalytic performance in the selective oxidation of propane to acrylic acid were compared in order to elucidate the roles of constituent elements and crystal structure in the course of the propane oxidation. It was observed that the rate of propane oxidation was almost the same over all three catalysts, revealing that Mo and V, which were indispensable elements for the structure formation, were responsible for the catalytic activity for propane oxidation. The Te-containing catalysts showed much higher selectivity to acrylic acid than the Mo V O catalyst. Since propene was formed as a main product at low conversion levels over every catalyst, it can be concluded that Te located in the central position of the hexagonal ring promoted the conversion of intermediate propene effectively to acrylic acid. The catalyst with Nb occupying the same structural position of V clearly showed the improved selectively to acrylic acid particularly at high conversion region, because the further oxidation of acrylic acid to CO x was greatly suppressed. These conclusions were further supported by the additional studies of the determination of activation energy and catalytic oxidations of intermediate products of the propane oxidation.