The reaction products and the stoichiometry of the urea catalytic decomposition in the system HNO3-HCOOH-Pt/SiO2 were studied with an application of the IR spectroscopy, the mass spectroscopy methods and chemical analysis. It was found that in the presence of 0.1g ml(-1) 1% PtSiO2, the 0.1-0.4 M (NH2)(2)CO decomposes at 50-90 degreesC in the solutions of 2.5-6.4 M HNO3 containing 0.25-1.5 M HCOOH according to a stoichiometric equation:3(NH2)(2)CO + 3HCOOH + 5HNO(3) --> 2N(2) + N2O + 2NH(4)NO(3) + NH2CHO + 5CO(2) + 6H(2)O.Soluble reaction products-the ammonium nitrate and the formamide-undergo further a gradual degradation under the conditions of a catalytic denitration reaction that starts when the urea decomposition is completed. (C) 2003 Elsevier Science B.V. All rights reserved.