A method includes supplying a gas containing acrolein to a fixed bed reactor including a reaction tube to produce acrylic acid by vapor phase catalytic oxidation of acrolein. The reaction tube is packed with catalysts having different activities in such a way that catalyst layers are formed in a tube axis direction. A catalyst X having the highest activity among the catalysts contained in all the catalyst layers is placed in the whole or a part of a section up to 30% of a length of all the catalyst layers from a rearmost portion on a gas outlet side toward a gas inlet side. A catalytically active component x in the catalyst X has Mo, V, and optionally Cu. When Cu is included, its amount is 0.8 mol or less per 12 mol of Mo. A specific surface area of the catalytically active component x is 15-40 m.sup.2/g.

A method includes supplying a gas containing acrolein to a fixed bed reactor including a reaction tube to produce acrylic acid by vapor phase catalytic oxidation of acrolein. The reaction tube is packed with catalysts having different activities in such a way that catalyst layers are formed in a tube axis direction. A catalyst X having the highest activity among the catalysts contained in all the catalyst layers is placed in the whole or a part of a section up to 30% of a length of all the catalyst layers from a rearmost portion on a gas outlet side toward a gas inlet side. A catalytically active component x in the catalyst X has Mo, V, and optionally Cu. When Cu is included, its amount is 0.8 mol or less per 12 mol of Mo. A specific surface area of the catalytically active component x is 15-40 m.sup.2/g.

Embodiments of the present invention include a filter element for decomposing contaminants including a substrate, and a photocatalytic composition comprising at least a photocatalyst and a co-catalyst. The embodiments of the present invention also includes a system for decomposing contaminants including a substrate, and a photocatalytic composition comprising at least a photocatalyst and a co-catalyst; and a method using the system.

Embodiments of the present invention include a filter element for decomposing contaminants including a substrate, and a photocatalytic composition comprising at least a photocatalyst and a co-catalyst. The embodiments of the present invention also includes a system for decomposing contaminants including a substrate, and a photocatalytic composition comprising at least a photocatalyst and a co-catalyst; and a method using the system.

Provided is a p-type TiO.sub.2/n-type WO.sub.3 heterojunction catalyst and a preparation method and use thereof. The catalyst comprises p-type TiO.sub.2 and n-type WO.sub.3 supported on a surface of the p-type TiO.sub.2.

An object of the present invention is to provide a catalyst capable of improving the selectivity of unsaturated aldehydes and unsaturated carboxylic acids, and a catalyst containing molybdenum, antimony, bismuth, and iron, wherein an atom ratio of the antimony to the molybdenum on a surface of the catalyst is greater than an atom ratio of the antimony to the molybdenum in the entire catalyst is provided.

An object of the present invention is to provide a catalyst capable of improving the selectivity of unsaturated aldehydes and unsaturated carboxylic acids, and a catalyst containing molybdenum, antimony, bismuth, and iron, wherein an atom ratio of the antimony to the molybdenum on a surface of the catalyst is greater than an atom ratio of the antimony to the molybdenum in the entire catalyst is provided.

The present invention relates to a method for producing a support at least micrometric in size, photocatalytically active and at least in the visible range, containing nanocrystals each composed of from 80 to 100 mol % of TiO.sub.2 and from 0 to 20 mol % of at least one other metal or semi-metallic oxide, comprising the following steps, from an acidic aqueous reaction medium, at a heating temperature of between 20 and 60° C.: a step of adding the titanium oxide precursor, or a mixture of the titanium oxide precursor and the precursor of the other oxide, in the acidic aqueous reaction medium, and a condensation step on or inside the support, by spraying onto the support or immersing the support in the aqueous reaction medium, for a specific period of condensation, a heating step, the support allowing the nanocrystals to be crystallized, without using surfactant, in the aqueous reaction medium, a step of rinsing with water and a recovery step on the one hand of the support on which the crystallization took place, these nanocrystals being attached by covalent bonds to the support, and on the other hand of a residual solution.

Provided is a composition for catalyst production which is used in the production of a catalyst for gas phase catalytic oxidation reaction or a catalyst for gas phase catalytic ammoxidation reaction, wherein the composition for catalyst production is an aqueous solution containing a niobium compound and hydrogen peroxide and optionally containing an organic acid, a molar ratio (organic acid/Nb) of a concentration of the organic acid to a Nb concentration is 0.00 or more and 2.00 or less, and a molar ratio (hydrogen peroxide/Nb) of a concentration of the hydrogen peroxide to a Nb concentration is 0.01 or more and 50 or less.

Provided is a composition for catalyst production which is used in the production of a catalyst for gas phase catalytic oxidation reaction or a catalyst for gas phase catalytic ammoxidation reaction, wherein the composition for catalyst production is an aqueous solution containing a niobium compound and hydrogen peroxide and optionally containing an organic acid, a molar ratio (organic acid/Nb) of a concentration of the organic acid to a Nb concentration is 0.00 or more and 2.00 or less, and a molar ratio (hydrogen peroxide/Nb) of a concentration of the hydrogen peroxide to a Nb concentration is 0.01 or more and 50 or less.