On the use of the first-order approximation in the kinetic analysis of TPR profiles

A theoretical investigation was carried out on the analysis of TPR profiles by the power-law kinetic model. Attention was focused on the use of the first-order approximation, with the aim to assess its limits in the procedure for estimating the activation energy of reduction. Numerical simulations performed by solving the non-isothermal mass-balance equations for the gaseous and solid species indicated a high sensitivity of the reduction patterns to the reaction order with respect to the solid. This quantity was found to exert a considerable influence on both the temperature at peak maximum and the peak shape. A large number of TPR profiles was generated, assuming reaction orders other than unity and activation energies ranging from 80 to 100 kJ mol(-1). These profiles were interpreted by means of the first-order power-law model. The results obtained showed that the unjustified assumption of the first-order approximation may introduce significant errors in the estimate of the activation energy. In several cases, real and estimated values differed by more than 30%. In order to provide some guidelines for a correct kinetic analysis, the causes responsible for such misinterpretation were investigated from both a qualitative and quantitative point of view.