Bismuth molybdate, catalysed oxidation

Among the oxide catalysts, bismuth molybdates that catalyse selective oxidation and ammoxidation of propylene to yield acrolein and acrylonitrile have received considerable attention (Grasselli Burrington, 1981) ... 

The first set of reactions is the mainstay of the petrochemical industry 1 outstanding examples are the oxidation of propene to propenal (acrolein) catalysed by bismuth molybdate, and of ethene to oxirane (ethylene oxide) catalysed by silver. In general these processes work at high but not perfect selectivity, the catalysts having been fine-tuned by inclusion of promoters to secure optimum performance. An especially important reaction is the oxidation of ethene in the presence of acetic (ethanoic) acid to form vinyl acetate (ethenyl ethanoate) catalysed by supported palladium-gold catalysts this is treated in Section 8.4. Oxidation reactions are very exothermic, and special precautions have to be taken to avoid the catalyst over-heating. 

The allyl radical, CsHs, is an intermediate in the selective oxidation of propene to acrolein with oxygen, catalysed by bismuth molybdate and iron antimonate [69,91]... 

In 1975, Ohloff etal. studied the gas-phase oxidation of ot-isophorone to KIP over a vanadia/pumice catalyst modified with 1 wt% of hthium phosphate at 230°C. Under these conditions, simultaneous formation of KIP and formylisophorone occurred. More than 20 years later, Baiker et al. revisited the catalytic gas-phase oxidation of isophorone. At 200-250°C, 75% combined yields of KIP and formyhsophorone were obtained at 17% ot-isophorone conversion over vanadia/pumice impregnated with hthium phosphate j6-isophorone was found as a major by-product (18%). Bismuth molybdate or vanadium phosphate showed poor selectivity and rapid deactivation. The Ag/y-alumina-catalysed oxidation was unselec-tive and resulted mainly in isomerisation to j6-isophorone. Chromia-based catalysts led to an increased formation of 3,5-xylenol. To efficiently remove coke deposits and to re-oxidise vanadium oxides to vanacha, temperatures higher than 300°C would be needed however, under these conditions isophorone and KIP are not stable. Thus, highly selective catalysts would be required which are active at lower temperatures. 

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