| abstract |
A method for preparing phthalic anhydride by the catalytic vapor phase oxidation of either ortho-xylene or naphthalene, which comprises passing a gas comprising a molecular oxygen, an inert gas and a member of the group consisting of ortho-xylene and naphthalene first through a catalyst A comprising a catalytically active substance on a porous inert carrier, said catalytically active substance consisting essentially of 1 to 20 parts by weight of V2O5, 99 to 80 parts by weight of anatase-type TiO2, and, based on the total weight of V2O5 and TiO2, 0.01 to 1.0% by weight of Nb2O5, 0.5 to 1.1% by weight of P2O5, 0 to 0.25% by weight of K2O and 0 to 0.5% by weight of Cs2O, the total weight of the K2O and Cs2O being at least 0.05% by weight, 0.05 to 0.3% by weight of Na2O and 0 to 0.5% by weight of Rb2O, said porous inert carrier comprising essentially SiC, and thereafter through a catalyst B comprising a catalytically active substance on a porous inert carrier, said catalytically active substance consisting essentially of 1 to 20 parts by weight of V2O5, 99 to 80 parts by weight of anatase-type TiO2, and, based on the total weight of the V2O5 and TiO2, 0.01 to 1.0% by weight of Nb2O5, 1.2 to 2.5% by weight of P2O5, 0 to 0.25% by weight of K2O and 0 to 0.5% by weight of Cs2O, the total weight of the K2O and Cs2O being at least 0.05% by weight, 0.05 to 0.3% by weight of Na2O and 0 to 0.5% by weight of Rb2O, said porous inert carrier comprising essentially SiC. |