Temperature-programmed reduction. Parametric sensitivity and estimation of kinetic parameters

Abstract

The influence of the different experimental operating variables used in temperature-programmed reduction (TPR) measurements on the reduction profiles has been studied using the reduction of nickel oxide as an example. The temperature range and the shape of the resulting TPR profiles were markedly affected by the experimental conditions. A characteristic number, K, is defined to aid in selecting the values for the operating variables which should be chosen in order to obtain optimum reduction profiles. The number relates the heating rate, hydrogen concentration, total flow rate, and the amount of reducible sample in such a way that the operating variables can easily be adjusted. Upper and lower limits are proposed for this characteristic number, and the influence of its variation on the sensitivity of the TPR method is discussed. Different methods for estimating the kinetic parameters of the reduction of nickel oxide from TPR experiments are compared. A peak shape analysis leads to narrower confidence limits for the kinetic parameters than an estimation based on the shift of the temperature of the maximum reduction rate measured for different heating rates. Simple criteria are proposed to check whether TPR measurements are free from mass transfer limitations.