1. Field of the Invention
The present invention relates to a method for preparing a catalyst used in producing methacrolein and methacrylic acid by the gas-phase catalytic oxidation of isobutylene or tert-butanol.
2. Description of the Prior Art
A large number of catalysts are known in regard to the production of methacrolein and methacrylic acid by the gas-phase catalytic oxidation of isobutylene or tert-butanol. Also, a large number of methods for producing the catalysts have been proposed. For example, Japanese Patent Application Kokai No. 57 12827 discloses that, in producing a multicomponent catalyst comprising molybdenum, bismuth, lead and antimony used in the ammoxidation of propylene, an aqueous slurry is adjusted to a pH of 7 or less. Further, U.S. Pat. No. 4,224,193 discloses that, in producing a multicomponent catalyst comprising molybdenum, bismuth, iron and an alkali metal (e.g. potassium, rubidium) used in the oxidation of propylene or isobutylene, it is preferred to finally adjust the pH of an aqueous slurry to 1 to 5. However, the above methods are complicated and expensive in producing a catalyst industrially. Further, since these methods require nitric acid or ammonia as a pH controlling agent, they have a problem that a large amount of NOx is generated when drying and baking the catalyst.