TRACER STUDIES OF OLEFIN OXIDATION OVER AN ALPHA-BI2MO3O12 CATALYST USING LASER RAMAN AND MICROWAVE SPECTROSCOPY

The oxide oxygen of alpha-Bi2Mo3O12 was exchanged via olefin oxidation using O-18(2). Band shifts in the Raman spectra of the catalyst were examined. In the oxidation of propene and trans-but-2-ene, the bands a t 865 and 845 cm(-1) of alpha-Bi2Mo3O12 were shifted preferentially. O xygen insertion apparently takes place at the vacancies on Mo-O tetrah edra associated with these bands. Four deuterated acrolein species obt ained from the oxidation of cis-CHD=CD-CH3 over alpha-Bi2Mo3O12 and Mo O3 catalysts were examined by microwave spectroscopy, The products exh ibited an isotope effect for the second hydrogen abstraction. This is consistent with a fast pi-allyl to sigma-allyl equilibration process o ver gamma-Bi2MoO6 as reported previously, These results were discussed with focus on the allyl intermediate associated with the catalyst and the oxide tetrahedra. In particular, specific Mo-O bonds in the alpha (1) and alpha(2) tetrahedra are identified as involved in the oxidatio n process. (C) 1998 Academic Press.