Kinetics of Thermal Dissociation of Ammonium Metavanadate

Abstract

The solid products of thermal decomposition of ammonium metavanadate can be used as catalysts in many important processes, and a knowledge of the dynamics of these processes is therefore essential. The thermal dissociation of ammonium metavanadate was studied under non-isothermal conditions in air atmosphere. This process occurred in three steps under the applied experimental conditions, and was associated with the elimination of ammonia and water below 330°C and with the formation of nitrogen oxides above 330°C. The kinetics of particular stages of (NH4)2OV205 decomposition was evaluated from the dynamic mass loss data by means of the integral method, with applycation of the Coats and Redfern approximation. The first stage of decomposition to ammonium hexavanadate is governed by a random nucleation model, the second step by a three-dimensional diffusion or contracting volume model, and the last stage again by a random nucleation model. The apparent activation energies found for the particular stages were 144.97, 378.31 or 184.40 and 260.65 kJ mol−1, respectively.