Dendritic Mesoporous Silica Nanoparticle-Supported Molybdena Catalysts for Propane Selective Oxidation: Catalytic Performance versus Molybdena Molecular Structure

Molybdena catalysts supported on dendritic mesoporous silica nanoparticles (Mo/DMSNs) were prepared by the impregnation method and evaluated for the selective oxidation of propane. The dendritic channels and high specific surface area of the DMSN support isolated the active components, which was beneficial for improving the dispersion of the Mo species. The identities of the active Mo species on the Mo/DMSN catalysts were determined using a combination of characterization techniques, and the relationship between the Mo loading and the structures of these Mo species was examined. Upon increasing the Mo loading, the mono-oxo O=Mo(O-Si)(4) and di-oxo (O=)(2)Mo(O-Si)(2) species underwent gradual polymerization to afford crystalline MoOx, where the mono-oxo and di-oxo species led to higher target product selectivities compared with the crystalline phase. In situ Raman spectroscopy results indicated that the highly dispersed monomolybdenum species were highly stable and resistant to carbon deposition during the reaction. Consequently, the 0.1Mo/DMSN, 0.5Mo/DMSN, and 1.0Mo/DMSN catalysts with monomolybdenum species exhibited higher propane conversions and target product selectivities than the catalysts bearing crystalline MoOx species. The highest yield (37.6%) of the target products (olefins and total aldehydes) was obtained over the 0.5Mo/DMSN catalyst at a temperature of 625 degrees C.