Abstract: This invention provides a method of reactivating a catalyst for methacrylic acid production, which catalyst is used in production of methacrylic acid through vapor-phase oxidation of methacrolein or vapor-phase oxidative dehydrogenation of isobutyric acid, contains P and Mo, and exhibits reduced activity. The process comprises treating the catalyst, whose activity level has dropped (deteriorated catalyst), with a gas containing a nitrogen-containing heterocyclic compound (e.g., pyridine, piperidine, piperazine, quinoline).

Abstract: The invention provides a method for regenerating with high efficiency a deteriorated catalyst of reduced activity, said catalyst originating from a heteropolyacid catalyst containing heteropolyacid formed of molybdophosphoric acid and/or molybdovanadophosphoric acid, or a salt thereof, to a heteropolyacid catalyst which exhibits approximately equivalent activity level to that of the fresh catalyst. Said method comprises mixing a deteriorated catalyst and a nitrogen-containing heterocyclic compound under the conditions whereunder ammonium ions and nitrate anions are present at such ratio that the amount of total ammonium ions per mol of total nitrate anions does not exceed 1.7 mols, drying the mixture and calcining the same.

Abstract: A novel method for preparing a heteropolyacid catalyst containing a heteropolyacid composed of molybdophosphoric acid and/or molybdovanadophosphoric acid, or a salt of the heteropolyacid, is provided.