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).
