Process for the vapor phase oxidation of benzene to maleic anhydrides

Claim 1

In a process for the vapor phase oxidation of benzene to maleic anhydride wherein a stream consisting essentially of said benzene, at about 1.1 to 1.6 mol % of benzene based on the total gaseous stream and a flow rate of 50 to 200 grams of benzene per hour and oxygen, is contacted at a temperature in the range of 340°-500° C with a fixed bed vanadium -- molybdenum -- oxygen catalyst, having an atomic ratio of molybdenum to vanadium in the range of 0.05 to 0.95:1 and containing less than 25 percent by weight of other components based on the total weight of molybdenum and vanadium, there being an exotherm of reaction in said catalyst bed and wherein said catalyst gradually decreases in activity, the improvement comprising adding to said stream a volatilizable compound of a phosphorus halide or an organo-phosphorus compound selected from the group consisting of ##STR2## wherein R is phenyl or an alkyl radical of one to 6 carbon atoms and X is H or R, to contact said catalyst in an amount to deactivate only the portion of said catalyst bed containing the exotherm of reaction which was present in said catalyst bed prior to the addition of said phosphorus compound, thereby moving said exotherm down stream into said catalyst bed.