Mesoporous mixed metal oxides are highly promising for applications in selective oxidation catalysis because of their tunable “bulk” and surface compositions, variable metal oxidation states, high surface areas, as well as large and uniform pore sizes. In particular, vanadium, molybdenum, antimony and niobium-based mixed oxide phases are very attractive for selective oxidation and ammoxidation of lower alkanes, such as propane. Mesoporous single oxide (vanadates [1], molybdate [1], and niobate [1-3]) and binary oxide system [4] have been reported. However, preparation of thermally stable mesoporous mixed multicomponent metal oxides with high specific surface areas still remains a challenging task.

In this work we explore the synthesis of bulk mesoporous and nanocrystalline orthorhombic (M1) Mo-V-Te-Nb-O catalysts inside the pore channels of ordered mesoporous hosts, such as SBA-15 silica and niobia. The use of such mesoporous hosts allows confining the synthesis of the catalytic Mo-V-Te-Nb-O phases to the nanoscale region of their pore space. The control over the size of the Mo-V-Te-Nb-O domains was explored by conducting hydrothermal synthesis of the M1 phase in the presence of mesoporous hosts. In the second approach, fresh Mo-V-Te-Nb-O synthesis solutions were impregnated into the porous hosts followed by a hydrothermal synthesis step. The bulk structures of the mixed metal oxides obtained were characterized by XRD, SAXS, SEM, high resolution TEM and Raman spectroscopy. The fixed-bed microreactor studies of propane oxidative dehydrogenation oxidation to acrylic acid and ammoxidation to acrylonitrile were complemented by in situ and operando Raman studies of these novel catalysts and reference mixed metal oxide catalysts supported on non-porous Nb2O5.

References:

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4. L.Yuan, V. V. Guliants, et al. J. Phys. Chem. B. 109 (2005) 49, 23250-23254.