Isobutene to methacrolein and methacrylonitrile

Research on the selective oxidation of isobutene is mainly focussed on bismuth molybdate-based catalysts. Under conditions which are optimal 

Maissant et al. [194] find a selectivity of 83% at 450°C (compared with 90% for acrolein) and an activity which is about ten times as large as in the case of propene oxidation (75 mol h 1 g 1) if a Bi/Mo = 1/1 catalyst is used. 

Ray and Chanda [261] studied bismuth molybdates (prepared by the method of Peacock [250,251]) in an integral flow reactor. At constant W/F = 8 g h mol-1 and a feed ratio isobutene/oxygen = 1/6, a maximum selectivity of 75% was found at 400—450°C. As with propene, the reaction is first order with respect to isobutene and the rate is independent of the oxygen pressure. The reoxidation of the catalyst is very fast. Assuming that the kinetics can be described by three parallel first-order reactions for the production of methacrolein, carbon monoxide and carbon dioxide, rate coefficients were calculated (Table 18). 

Mann and Ko [202] likewise examined the selective oxidation of isobutene on bismuth molybdate. With an integral flow reactor, the highest selectivity was obtained at over 30% conversions for an oxygen/olefin ratio of 2/1 and a W/F = 2.5 g h mol-1 (390°C). The data were correlated with a rather complicated Langmuir—Hinshelwood expression inconsistent with a redox mechanism. This was based on a rate-controlling step between adsorbed isobutene and adsorbed oxygen, and included an inhibiting effect of methacrolein by competitive adsorption with isobutene, viz. 

Muizebelt and Van Ooij [234] studied catalysts of general formula 

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