Kinetic features and lattice-oxygen participation in propene oxidation over Bi–Mo oxide and some Mo oxide catalysts

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Abstract
The rates of propene conversion in the absence of oxygen have been compared with those in the presence of oxygen at the same propene pressures. Over Bi–Mo oxides which are mainly composed of the β- or γ-phase, the rates for propenal formation were 3.5–4.5 times bigger in the presence of oxygen than in the absence of oxygen. In contrast, some Mo-containing oxide catalysts such as MoO3, Co–Mo (1/1), Co–Te–Mo (1/1/1) and other Bi–Mo oxides exhibit little or no difference in the rates of propenal formation in the presence or absence of oxygen. In the case of but-1-ene and (E)-but-2-ene oxidation, both rates were nearly the same even on β- and γ-phase Bi–Mo oxides. Such a sensitive effect of oxygen on propenal formation over β- and γ-phase oxides seems to originate from an appreciable increase of active sites owing to a reoxidation step. Using 18O tracer studies in propene oxidation, the extents of lattice-oxygen participation were determined over various Mo oxide catalysts. The number of active sites for propene oxidation was found to be closely related to the extent of lattice-oxygen participation. A modified redox mechanism was proposed on the basis of a different active site model for the reduction and reoxidation steps. The kinetic features were discussed using this model.

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