Kinetics of the urea catalytic decomposition reaction in the system (NH2)(2)CO-HNO3-HCOOH were studied in the presence of the catalyst 1% PtSiO2.It was shown that a platinum catalyzed decomposition of urea in 2-8 M HNO3 proceeds in the presence of 0.2-1.5 M formic acid as a result of the reaction with nitrous acid generated in the process of catalytic denitration. The decomposition proceeds according to a "zero"-order with respect to the urea concentration and exhibits an induction period for [HNO3] < 2.5 M. The order of the process with respect to [HCOOH] is 1. The rate of reaction decreases when the concentration of nitric acid is increased that is explained by the hydrogen ions competitive adsorption on the catalyst's surface. The rate-determining step of the urea catalytic decomposition is a reaction of heterogeneous catalytic formation of nitrous acid.It was found that an activity of the Pt/SiO2 catalyst decreases reversibly with the increase of the drying temperature during its regeneration. (C) 2003 Elsevier Science B.V. All rights reserved.