Abstract: A process for reactivating a vanadium-containing oxidation catalyst, wherein the catalyst is treated first at from 100.degree. to 600.degree. C., with a volatile phosphorus compound in the presence of an oxygen-containing gas, and then at from 50.degree. to 600.degree. C. with sulfur trioxide or a mixture of a volatile sulfur compound and an oxygen-containing gas.

Abstract: A supported catalyst, containing vanadium pentoxide, titanium dioxide, phosphorus, rubidium and any optionally added cesium, with or without zirconium dioxide, in which the catalytic material contains from 1 to 40% by weight of V.sub.2 O.sub.5, from 60 to 99% by weight of TiO.sub.2 and/or ZrO.sub.2 and, based on the total amount of TiO.sub.2, ZrO.sub.2 and V.sub.2 O.sub.5, up to 2% by weight of phosphorus and up to 1.5% by weight of rubidium and/or cesium, and which comprises two layers, of which the inner layer contains more than 0.2 and up to 2% by weight of phosphorus, but no rubidium and/or cesium, and the outer layer contains from 0 to 0.2% by weight of phosphorus and from 0.02 to 1.5% by weight of rubidium and/or cesium, the outer layer accounting for from 10 to 90% by weight of the total catalytic material.

Abstract: A supported catalyst, containing vanadium and titanium and/or zirconium, obtained by applying a mixture of finely divided titanium dioxide and/or zirconium dioxide, and a solution or suspension of a vanadium compound, to an inert, non-porous, ring-shaped carrier having an external diameter of from 6 to 10 mm, a length of from 4 to 10 mm and a wall thickness of from 0.5 to 3 mm, the two end faces of the ring-shaped carrier being outwardly beveled at an angle such that the length of the outer cylindrical wall is at least 20% shorter than the length of the inner cylindrical wall.

Abstract: A supported catalyst for the oxidation of aromatic or unsaturated aliphatic hydrocarbons, comprising an inert nonporous carrier to which is applied a thin layer of a catalytic composition which contains from 1 to 39.9 percent by weight of vanadium pentoxide, from 60 to 98.9 percent by weight of titanium dioxide and from 0.1 to 10% by weight of rubidium and antimony in an atomic ratio Rb : Sb of from 1:2.5 to 1:30, the vanadium pentoxide content being from 0.05 to 4 percent by weight, based on the supported catalyst.

Abstract: A process for the manufacture of phthalic anhydride by oxidizing o-xylene and/or naphthalene over a supported catalyst containing vanadium pentoxide and titanium dioxide, at from 350.degree. to 500.degree. C, in which the o-xylene or naphthalene is passed, with an oxygen-containing carrier gas, over the catalyst, and in which the catalyst in the first 25-50 per cent by volume of the total catalyst volume, in the direction of flow of the mixture of o-xylene or naphthalene and carrier gas, contains from 0.01 to 0.3 per cent by weight, based on titanium dioxide, of rubidium, but no phosphorus, in the active composition, while the remainder of the catalyst contains from 0.02 to 0.8 per cent by weight, based on titanium dioxide, of phosphorus, but no rubidium, in the active composition.

Abstract: A supported catalyst containing vanadium and titanium, comprising a ring-shaped carrier having an external diameter of from 7.3 to 8.6 mm, a length of from 5.3 to 7 mm and a wall thickness of from 0.1 to 2 mm, and an active composition, applied thereto, of from 1 to 30 per cent by weight of vanadium pentoxide and from 70 to 99 per cent by weight of titanium dioxide and/or zirconium dioxide.

Abstract: Supported catalyst for the oxidation of o-xylene or naphthalene to phthalic anhydride, comprising an inert carrier and the active material applied thereto, which contains from 1 to 40 per cent by weight of vanadium pentoxide, from 60 to 98.84 per cent by weight of titanium dioxide and from 0.16 to 0.6 per cent by weight, based on titanium dioxide, of rubidium in the form of rubidium oxide, the vanadium pentoxide content being from 0.05 to 4 per cent by weight, based on the (complete) catalyst.