Platinum is applied on a carrier such as graphite to form a platinum catalyst. The catalyst becomes poisoned with a metal as a result of use of the catalyst in preparation of hydroxylammonium salts. A method of regenerating the catalyst dissolves the platinum and the metal in an acid. The method also adds ammonium sulfate to the acid to precipitate the platinum. The ammonium sulfate is a by-product of a commercial process to synthesize a caprolactam. Also, the method precipitates the platinum onto the carrier for reuse in the preparation of the hydroxylammonium salts and in preparation of the caprolactam.