Oxides 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... 

Fig. 10.5. Mechanistic representation of propene oxidation over bismuth-lead molybdate.

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. 

Many other substances have been tested for use as additives for molybdenum disulphide films, including silver, tin, lead, lead oxide, bismuth trioxide and boron nitride , alumina, arsenic oxide, cadmium oxide, cuprous oxide, molybdic oxide. 

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... 

Burlamacchi et al. [65,66] also used ESR techniques and found that CdMo04 differs from Bi2Mo06 in adsorbing molecular oxygen. The oxygen is activated through the formation of radicals on the surface and leads to deeper oxidation than bismuth molybdate. 

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