Bulk mixed Mo–V–Te–O catalysts for propane oxidation to acrylic acid

Abstract

The model Mo–V–Te–O catalysts containing the orthorhombic (M1) and hexagonal (M2) phases with well-defined crystal morphologies and promising for the selective oxidation of propane to oxygenates were obtained hydrothermally over a wide range of synthesis compositions (Mo 0.70–0.30V 0.60–0.20Te 0.15–0.05). The bulk (ICP), local (EDS) elemental and structural (XRD) analyses of this compositionally simple model system indicated that the M1 phase with the bulk Mo/V ratio of ∼2 was dominant in the Mo–V–Te–O catalysts. This phase has been proposed as active and selective for propane oxidation to oxygenates and ammoxidation to acrylonitrile. The model catalysts displayed high selectivity to acrylic acid in the presence of water vapor in the feed, which is believed to enhance the apparent rates of formation of oxygenates as well as maintain the catalytic surface in a partially reduced oxidation state. The selectivity to acrylic acid over these model catalysts correlated with the extent of exposure of the surface ab planes of the M1 phase proposed to contain the active and selective surface sites. Therefore, the Mo–V–Te–O catalysts represent a well-defined and highly promising model system for elucidating the surface molecular structure–activity/selectivity relationships in propane oxidation to acrylic acid over multicomponent Mo–V–Te–Nb–O catalysts.