Geoffrey C. Bond, S. Flamerz Tahir
Apr 4, 1991
Citations
3
Influential Citations
536
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Journal
Applied Catalysis
Abstract
Abstract The purpose of this review is to provide a guide to the recent literature on the preparation, structure and catalytic properties of vanadium oxide monolayer catalysts. Monolayers of vanadium oxide, represented as VO χ , may be formed on the surface of a supporting oxide by impregnation with a suitable vanadium source, followed by calcination, by grafting methods using VOCl 3 or a vanadyl alkoxide, by heating mechanical mixtures or by coprecipitation. Information on the chemical structures present when there is less than a monolayer of VO χ can be obtained from vibrational and electron spectroscopies (Raman, FT-IR, XPS). Temperature-programmed reduction (TPR), XRD, ESR and 51 V NMR provide additional characterisation of the materials. VO χ monolayers are particularly stable on TiO 2 and on Al 2 O 3 , but are not readily formed on SiO 2 , where aggregation to V 2 O 5 occurs. At low vanadium contents, isolated VO 4 tetrahedra have been detected, and polymeric octahedral VO 6 species at higher loadings: various disordered and ‘paracrystalline’ V 2 O 5 phases have been seen when more than the monolayer loading is present. Species in the monolayer are effective catalysts for oxidation of o-xylene to phthalic anhydride, for ammoxidation of aromatics and for selective reduction of nitric oxide by ammonia, but not for oxidation of butadiene to maleic anhydride.