The present invention provides a method for producing an oxide catalyst containing antimony, comprising

a step (A) of obtaining the oxide catalyst using antimony particles containing a diantimony trioxide as a source of the antimony,

wherein an abundance of a pentavalent antimony in a surface layer of the antimony particle to be measured in XPS analysis is less than 70 atom %, and

the antimony particle has an average particle size of 1.2 m or less.

Polymerization inhibitor compositions are provided. The polymerization inhibitor compositions may include at least one hydroxylamine of a nitroxide and at least one phenylenediamine. Methods of inhibiting the unwanted polymerization of monomers are also provided. The methods include adding the presently disclosed polymerization inhibitor compositions to a fluid containing the monomers. The monomers may be ethylenically unsaturated monomers, such as acrylic acid, methacrylic acid, acrylonitrile, methacrylonitrile, acrolein, methacrolein, acrylate, methacrylate, acrylamide, methacrylamide, vinyl acetate, butadiene, ethylene, propylene, and styrene.

Polymerization inhibitor compositions are provided. The polymerization inhibitor compositions may include at least one hydroxylamine of a nitroxide and at least one phenylenediamine. Methods of inhibiting the unwanted polymerization of monomers are also provided. The methods include adding the presently disclosed polymerization inhibitor compositions to a fluid containing the monomers. The monomers may be ethylenically unsaturated monomers, such as acrylic acid, methacrylic acid, acrylonitrile, methacrylonitrile, acrolein, methacrolein, acrylate, methacrylate, acrylamide, methacrylamide, vinyl acetate, butadiene, ethylene, propylene, and styrene.

A method for producing an oxide catalyst according to the present invention is a method for producing an oxide catalyst containing Mo, V, Sb, and Nb, the method including: a raw material preparation step of obtaining an aqueous mixed liquid containing Mo, V, Sb, and Nb; an aging step of subjecting the aqueous mixed liquid to aging at more than 30 C.; a drying step of drying the aqueous mixed liquid, thereby obtaining a dried powder; and a calcination step of calcining the dried powder, thereby obtaining the oxide catalyst, wherein, in the raw material preparation step and/or the aging step, precipitation of Nb is facilitated by performing at least one operation selected from the group consisting of the following (I) to (III): (I) in the raw material preparation step, the aqueous mixed liquid is prepared by mixing a Nb raw material liquid containing Nb with a MoVSb raw material liquid containing Mo, V, and Sb, wherein ammonia is added to at least one of the MoVSb raw material liquid, the Nb raw material liquid, and the aqueous mixed liquid such that a molar ratio in terms of NH.sub.3/Nb in the aqueous mixed liquid is adjusted to be 0.7 or more, and in the aging step, a temperature of the aqueous mixed liquid is adjusted to more than 50 C.; (II) in the aging step, a temperature of the aqueous mixed liquid is adjusted to more than 65 C.; and (III) in the raw material preparation step, the aqueous mixed liquid is prepared by mixing a Nb raw material liquid containing Nb with a MoVSb raw material liquid containing Mo, V, and Sb, wherein a molar ratio in terms of H.sub.2O.sub.2/Nb in the Nb raw material liquid is adjusted to less than 0.2, and in the aging step, a temperature of the aqueous mixed liquid is adjusted to more than 50 C.

A method for producing an oxide catalyst according to the present invention is a method for producing an oxide catalyst containing Mo, V, Sb, and Nb, the method including: a raw material preparation step of obtaining an aqueous mixed liquid containing Mo, V, Sb, and Nb; an aging step of subjecting the aqueous mixed liquid to aging at more than 30 C.; a drying step of drying the aqueous mixed liquid, thereby obtaining a dried powder; and a calcination step of calcining the dried powder, thereby obtaining the oxide catalyst, wherein, in the raw material preparation step and/or the aging step, precipitation of Nb is facilitated by performing at least one operation selected from the group consisting of the following (I) to (III): (I) in the raw material preparation step, the aqueous mixed liquid is prepared by mixing a Nb raw material liquid containing Nb with a MoVSb raw material liquid containing Mo, V, and Sb, wherein ammonia is added to at least one of the MoVSb raw material liquid, the Nb raw material liquid, and the aqueous mixed liquid such that a molar ratio in terms of NH.sub.3/Nb in the aqueous mixed liquid is adjusted to be 0.7 or more, and in the aging step, a temperature of the aqueous mixed liquid is adjusted to more than 50 C.; (II) in the aging step, a temperature of the aqueous mixed liquid is adjusted to more than 65 C.; and (III) in the raw material preparation step, the aqueous mixed liquid is prepared by mixing a Nb raw material liquid containing Nb with a MoVSb raw material liquid containing Mo, V, and Sb, wherein a molar ratio in terms of H.sub.2O.sub.2/Nb in the Nb raw material liquid is adjusted to less than 0.2, and in the aging step, a temperature of the aqueous mixed liquid is adjusted to more than 50 C.

A process for producing unsaturated nitrile, using a fluidized bed reactor having an internal space having a catalyst capable of being fluidized therein, a feed opening to feed a starting material gas comprising hydrocarbon to the internal space, and a discharge port to discharge a reaction product gas from the internal space, the process comprising a reaction step of subjecting the hydrocarbon to a vapor phase catalytic ammoxidation reaction in the presence of the catalyst in the internal space to produce the corresponding unsaturated nitrile, wherein when in the internal space, a space where an existing amount of the catalyst per unit volume is 150 kg/m.sup.3 or more is defined as a dense zone and a space where an existing amount of the catalyst per unit volume is less than 150 kg/m.sup.3 is defined as a sparse zone in the reaction step, a gas residence time in the sparse zone is 5 to 50 sec.

A process for producing unsaturated nitrile, using a fluidized bed reactor having an internal space having a catalyst capable of being fluidized therein, a feed opening to feed a starting material gas comprising hydrocarbon to the internal space, and a discharge port to discharge a reaction product gas from the internal space, the process comprising a reaction step of subjecting the hydrocarbon to a vapor phase catalytic ammoxidation reaction in the presence of the catalyst in the internal space to produce the corresponding unsaturated nitrile, wherein when in the internal space, a space where an existing amount of the catalyst per unit volume is 150 kg/m.sup.3 or more is defined as a dense zone and a space where an existing amount of the catalyst per unit volume is less than 150 kg/m.sup.3 is defined as a sparse zone in the reaction step, a gas residence time in the sparse zone is 5 to 50 sec.

It is an object of the present invention to provide a composite oxide catalyst which can suppress the generation of CO.sub.2 and CO and improve the yield of an unsaturated nitrile in a method for subjecting propane or isobutane to a vapor-phase catalytic ammoxidation reaction to produce a corresponding unsaturated nitrile, and a method for producing the composite oxide catalyst, and a method for producing an unsaturated nitrile using the composite oxide catalyst. A composite oxide catalyst used for a vapor-phase catalytic oxidation reaction or vapor-phase catalytic ammoxidation reaction of propane or isobutane, the composite oxide catalyst comprising a composite oxide represented by the following composition formula (1):
Mo.sub.1V.sub.aSb.sub.bNb.sub.cW.sub.dZ.sub.eO.sub.n(1),
wherein the component Z is one or more element selected from the group consisting of La, Ce, Pr, Yb, Y, Sc, Sr, and Ba; a, b, c, d, e, and n represent atomic ratios of the elements; and 0.1a<0.2, 0.15b0.5, 0.01c 0.5, 0d0.4, 0e0.2, and 0.60<a/b<1.00.

It is an object of the present invention to provide a composite oxide catalyst which can suppress the generation of CO.sub.2 and CO and improve the yield of an unsaturated nitrile in a method for subjecting propane or isobutane to a vapor-phase catalytic ammoxidation reaction to produce a corresponding unsaturated nitrile, and a method for producing the composite oxide catalyst, and a method for producing an unsaturated nitrile using the composite oxide catalyst. A composite oxide catalyst used for a vapor-phase catalytic oxidation reaction or vapor-phase catalytic ammoxidation reaction of propane or isobutane, the composite oxide catalyst comprising a composite oxide represented by the following composition formula (1):
Mo.sub.1V.sub.aSb.sub.bNb.sub.cW.sub.dZ.sub.eO.sub.n(1),
wherein the component Z is one or more element selected from the group consisting of La, Ce, Pr, Yb, Y, Sc, Sr, and Ba; a, b, c, d, e, and n represent atomic ratios of the elements; and 0.1a<0.2, 0.15b0.5, 0.01c 0.5, 0d0.4, 0e0.2, and 0.60<a/b<1.00.

A method for producing a catalyst according to the present invention includes: a preparation step of preparing a precursor slurry comprising molybdenum, bismuth, iron, silica, and a carboxylic acid; a drying step of spray-drying the precursor slurry and thereby obtaining a dried particle; and a calcination step of calcining the dried particle, wherein the preparation step comprises: a step (I) of mixing a starting material for silica with the carboxylic acid and thereby preparing a silica-carboxylic acid mixed liquid; and a step (II) of mixing the silica-carboxylic acid mixed liquid, molybdenum, bismuth, and iron.