Patent ID: 6362345
Filing Date: 2002-03-26
Classification: C07C

Abstract:
A process for preparing phthalic anhydride by catalytic gas-phase oxidation of o-xylene/naphthalene mixtures by molecular oxygen usinga catalyst I in a first zone on the gas inlet side which makes up from 25 to 75 percent by volume of the total catalyst volume, comprising, in each case based on the catalytically active composition, from 1 to 10% by weight of vanadium oxide (calculated as V2O5), from 1 to 10% by weight of antimony oxide (calculated as Sb2O3) and from 80 to 98% by weight of titanium dioxide of the anatase type having a BET surface area of from 13 to 28 m2/g and also from 0.05 to 1% by weight of cesium (calculated as Cs) applied to a steatite support and a catalyst II in a second zone which makes up the remaining 75 to 25 percent by volume of the total catalyst volume, comprising, in each case based on the catalytically active composition, from 1 to 10% by weight of vanadium oxide (calculated as V2O5), from 1 to 10% by weight of antimony oxide (calculated as Sb2O3) and from 80 to 98% by weight of titanium oxide of the anatase type having a BET surface area of from 13 to 28 m2/g and from 0.01 to 1% by weight of phosphorus oxide (calculated as P) and also from 0.01 to 0.2% by weight of cesium (calculated as Cs) applied to a steatite support, wherein the cesium content of the catalyst II is less than 15% by weight of the cesium content of the catalyst I and the catalyst I and the catalyst II have been prepared without addition of compounds of niobium.