Effect Of Catalyst Preparation And Surface Modification Synthesis And Nanostructuring Of Movtenb Oxide Catalyst For Propane Oxidation To Acrylic Acid

Author :
Publisher :
ISBN 13 :
Total Pages : 189 pages
Book Rating : 4.:/5 (227 download)

DOWNLOAD NOW!

Download or read book Mesoporous and Macroporous Mixed Metal Oxide MoVTeNbOx Catalysts for Propane (amm) Oxidation written by and published by . This book was released on 2008 with total page 189 pages. Available in PDF, EPUB and Kindle. Book excerpt: Approximately 5 million metric tons of acrylonitrile are produced worldwide annually for the manufacture of acrylic fibers, copolymers and reinforced carbon fibers. There is currently intense commercial interest in developing a new catalytic process for acrylonitrile production via propane ammoxidation employing multicomponent mixed metal oxides, which would replace the existing propylene ammoxidation technology. This new technology is expected to lower the production cost by 30% as compared to the existing process because of the lower cost of propane and increased production of valuable co-products, such as acetonitrile. The key to the success of this important technology is the development of novel mixed metal oxide catalysts that can selectively ammoxidize propane to acrylonitrile. Recent developments in macroscale and mesoscale structure-directed self-assembly offer many attractive possibilities for the molecular design of novel catalytic mixed metal oxides. The present work describes the development of novel synthesis approaches for macroporous and mesoporous mixed metal MoVTe(Sb)NbOx catalysts displaying ordered porous structures, high surface areas, flexible compositions and improved thermal stability for propane ammoxidation. This research began with systematic exploration of synthesis of mesoporous Nb2O5 oxides as a departure point in the subsequent synthesis of mixed M-Nb-O (M=Mo, V, Te, Sb) oxides employing Nb2O5 as the major component or the catalytic support. Nb2O5 was chosen for this study as the most stable metal oxide possessing the highest Tammann temperature among all constituent metal oxides (MoOx, VOx, TeOx and SbOx). Thermally stable (up to 500 °C) and well-defined two-dimensional hexagonal mesostructured niobium oxides were obtained possessing the surface areas of up to 210 m2/g. The pore size of mesoporous niobium oxides was for the first time tuned in a wide range from 4.6 to 21 nm by varying synthesis conditions. As compared with previous studies, mesoporous niobium oxides with tunable pore sizes obtained in this work possessed more attractive pores structures which make them promising as catalytic supports or a major component in the synthesis of improved MoVTeNbOx catalysts for selective (amm)oxidation of propane. Thermally stable mesoporous binary (Nb-M-O, M=Mo, V, or Sb), multicomponent (MNbOx, M=Mo+V+Te) and supported (M/Nb, M=Mo+V+Te+Nb) mixed metal oxide catalysts were for the first time synthesized by evaporation-induced self-assembly and incipient-wetness impregnation techniques. These mixed metal oxide phases displayed good thermal stability of amorphous inorganic wall (up to 400°C), large pore sizes (5-23 nm), high surface areas (up to 232 m2/g) and flexible inorganic wall compositions. Improved dispersion of active components in the Nb2O5 matrix and over the Nb2O5 support was observed. However, the desirable M1 phase was not observed in the products of thermal transformation of these mesoporous mixed metal oxides probably due to insufficient thickness of inorganic walls in these phases. In order to investigate nucleation of the catalytic M1 phase and further improve the thermal stability of the ordered porous structure, MoVTeNbOx phases displaying both macroporous and mesoporous structures were prepared by a dual templating approach employing colloidal arrays of polystyrene spheres and non-ionic surfactants. The MoVTeNbOx phases possessing such dual porosity were obtained after polystyrene spheres and non-ionic surfactants were removed in a low temperature calcination step. These hierarchical MoVTeNbOx phases displaying bimodal pore structure transformed into macroporous rutile phase possessing nanocrystalline inorganic walls at high temperature. These MoVTeNbOx rutile phases possessed high surface areas (70 m2/g), desirable pore architectures, robust nanocrystalline inorganic walls and enhanced thermal stability (up to 600 °C). Although these macroporous MoVTeNbOx rutile catalysts displayed lower activity in propane ammoxidation and lower acrylonitrile selectivity in propane ammoxidation as compared to the active and selective M1 phase, the novel synthesis method reported in these studies represents a promising general approach to design novel complex mixed metal oxides for a wide range of applications in selective oxidation catalysis.