Effect of tellurium on catalytic properties of vanadium-molybdenum oxide catalysts in oxidation of propylene and isobutylene

Abstract

CATALYSTS prepared from vanadium and molybdenum oxides are widely used for oxidation of hydrocarbons. These catalysts with A1 [2], Te [3] and P [4] additives, or without additives, can be used for the oxidation of unsaturated aldehydes or olefins (propylene, isobutylene) to corresponding acids. Considerable attention has been given in previous studies [5-8] to the V-Mo-O catalytic system. This paper [9] is concerned with the oxidation of propylene and isobutylene on V-Mo-O catalysts of different compositions under conditions of considerable dilution with steam of the initial reaction mixture. Two maxima were observed under these conditions during oxidation of isobutylene in the specific rate of formation of aldehydes and acids: withMo contents of 30 and 80 at.%. Acid yield for the isobutylene reacted is about the same with a Mo content in the catalyst of 30-80 at. %. During the oxidation of propylene maximum specific rate of acid formation is observed with a catalyst containing about 30 at.% Mo. For catalysts of this composition maximum yield is also observed for the reacted propylene. It is also established that during the oxidation of propylene acid yield is about twice as high as that during oxidation of isobutylene, however, as in the first process, acetic acid is the main product in the second; during oxidation of isobutylene the selectivity of formation of methacrylic acid is somewhat higher than that of acrylic acid in oxidation of propylene. Most satisfactory selectivity for unsaturated acid was observed with oxidation of isobutylene on a catalyst with 80 at. % Mo. Subsequently, we determined the acidity of the catalysts studied as it is well known to be important in some processes [10-12]. Acidity was determined by a method previously described [13] by titration with n-butylamine of catalyst samples suspended in benzene after activation and testing catalytic activity. When determining the acidity of the V-Mo-O system it was established that