The performance of denitration catalysts is usually evaluated according to the concentrations of No-3(-), NO2- and NH4+ ions. Catalytic conversion is conventionally calculated from the decrease of NO3- and NO2- in the reaction solution. In this study, batch experiments were performed by contacting NO2- with Pt/Al2O3 under the presence or absence of H-2 flow. Significant amounts of NO2- in the reaction solution disappeared even in the absence of H-2, i.e., under conditions where reduction did not occur. This phenomenon is explained by NO2-adsorption onto Al2O3. The equilibrium amount of adsorbed NO2- showed a linear decrease with the increase of Pt particles. The adsorption of NO2- onto Al2O3 should be considered when the performance of denitration catalysts is evaluated. In addition, utilizing the high adsorption capacity of Al2O3 for NO2- may realize its potential as a scavenger for the removal of NO2- ions in waste water. (C) 2009 Elsevier B.V. All rights reserved,