Macro and mesoporous mixed metal oxides for the partial oxidation of lower alkanes

The present work describes the development of novel synthesis methods for macro- and mesoporous vanadium phosphorus oxide (VPO) catalysts displaying highly ordered porous structures, high surface areas, optimal chemical environment (bulk compositions and vanadium oxidation states) and improved thermal stability for the partial oxidation of lower alkanes. Selective alkane oxidation lies at the heart of petroleum and petrochemical processing, as more than 60% of the chemicals and intermediates synthesized via catalytic processes are products of oxidation. Current synthesis approaches for the preparation of VPO catalysts offer limited control over structural, compositional and morphological properties which limits their catalytic performance. Recent developments of macro- and meso-scale structure-directed self-assembly approaches provide many attractive possibilities for the molecular design of novel catalytic mixed metal oxides. For the macroporous templated approach, densely packed monodisperse polystyrene spheres (0.4--0.7 mum in diameter) were used as templates for the formation of different macroporous VPO phases. For the synthesis of mesoporous VPO, alkyltrimethyl ammonium bromides and primary alkyl amines were used as cationic surfactants. Monododecyl phosphate, sodium hexadecane sulphonate and dodecyl sodium sulfate salt were used as anionic surfactants.;The macroporous VPO phases obtained displayed high surface areas (75 m2/g), desirable pore architectures, optimal chemical environment (i.e. bulk compositions and vanadium oxidation states) and the preferential exposure of the (100) surface plane of (VO)2P2O 7, the proposed active and selective phase for n-butane oxidation to maleic anhydride. Ordered lamellar, hexagonal and cubic mesostructured VPO phases with high surface areas (∼250 m2/g) displaying improved thermal stability, desirable bulk compositions (P/V∼1.1) and oxidation states (3.8--4.3) for the partial oxidation of lower alkanes were obtained using the proposed templated self-assembly approach. Interestingly, for the first time several phase transformations were observed for mesostructured VPO phases during post-synthesis treatments and explained by changes in " g", the surfactant packing parameter. The mesoscale self-assembly methods were extended to obtain other mesostructured mixed metal oxide systems (i.e. Mo-V-Nb oxides). The catalytic performance of these novel mixed metal oxide phases was studied for two selective oxidation processes: (1) n-butane oxidation to maleic anhydride and (2) propane ammoxidation to acrylonitrile.*.;*This dissertation is a compound document (contains both a paper copy and a CD as part of the dissertation). The CD requires the following system requirements: Microsoft Office.