Vapour-phase air oxidation of isobuthylene over bismuth-molybdate catalysts

Abstract

The vapor-phase air oxidation of isobutylene to methacrolein over bismuth molybdate catalysts were investigated in an isothermal integral flow reactor at atmospheric pressure between 300 and 600℃. Various bismuth molybdates were characterized by X-ray diffraction, in spectra, and DTA analysis as α-, β-, γ-bismuth molybdate. With these defined catalysts activity test was carried out. γ-Bismuth molybdate had the highest activity for the oxidation of isobutylene of the three catalysts. Then, for the study of kinetics of oxidation of isobutylene over γ-bismuth molybdate catalyst the effects of several variables, feed ratio of oxygen to isobutylene, reaction temperature and the reciprocal of space velocity on the conversion and product distribution were determined by gas chromatography. Through 13 different mechanisms were postulated, the rate of reaction was most satisfactorily correlated by a mechanism which assumes the rate-controlling step to be the surface reaction between charged adsorbed isobutylene and oxygen. The rate expression $$γ= \frac{K_SK_AP_A}{1+K_AP_A+K_RP_R}×\frac{K_BP_B}{1+K_BP_B}$$ fitted the data best. And derived rate and adsorption coefficients satisfy the Boudart criteria.