Oxide catalysts bismuth lead molybdate

The catalytic activity of bismuth-lead molybdate catalysts is related to the defect site densities. Olefin oxidations take place most rapidly when ( ) = 0.06. Acrylonitrile is formed by the ammoxidation of propene in about 75% yield over these mixed oxides when <(> is between 0.04 and 0.08.38... 

McCain et al. (17) oxidized CH3—CH=13CH2 over bismuth phospho-molybdate at 450°C. They observed equal distribution of 13C in the terminal carbons of acrolein and also postulated a symmetrical intermediate. They suggested, however, that a symmetrical species could be formed from propylene by either the addition or the abstraction of a hydrogen atom by the catalyst. This would lead to the following scheme. 

The mechanism of the allyl oxidation of propene is explained in terms of a reaction cycle [19]. As shown in Scheme 8-6, propene and air do not react directly with one another. Instead, the propene initially forms a n complex A witii an Mo center of the bismuth molybdate catalyst. Hydrogen abstraction by an oxo oxygen atom on bismuth leads to formation of a hydroxyl group and a 7i-aUyl complex at Mo B, whereby one... 

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