Abstract: A method of producing maleic anhydride by oxidizing a hydrocarbon material selected from unsaturated hydrocarbons having four or more of carbon atoms, butane and mixtures thereof with molecular oxygen or a molecular oxygen containing gas in gaseous phase and in the presence of a catalyst. The catalyst used in this method is of the type which contains vanadium, phosphorus, potassium and iron, and these components are contained in the following ratios per atom of vanadium: phosphorus, 2/3 to 140 atoms; potassium, 1/4 to 2 atoms; and iron, 1/10 to 70 atoms. Preferably the atomic ratio of phosphorus/iron is greater than 1.

Abstract: In a method of preparing maleic anhydride by oxidizing an unsaturated hydrocarbon or a mixture of unsaturated hydrocarbons having 4 or more carbon atoms in each molecule, there is used a catalyst comprising a mixed or complex oxide having the chemical composition:P.sub.a Mo.sub.b Bi.sub.c Cu.sub.d X.sub.e O.sub.fwhere X represents one or more members selected from the group consisting of iron, cobalt, nickel and potassium or the group consisting of iron, cobalt and nickel; a, b, c, d, e and f represent the number of atoms of P, Mo, Bi, Cu and O, respectively, e represents the sum of the number of atoms of the member or members represented by X; and the value of f is determined by the values of a, b, c, d and e and the valencies of P, Mo, Bi, Cu and O. Further addition of an alkali and/or alkaline earth metal as a component in the catalyst results in the improvement of the activity of the catalyst.