New Approach to the Investigation of Mechanisms and Apparent Activation Energies for the Reduction of Metal Oxides Using Constant Reaction Rate Temperature-Programmed Reduction

Abstract

A new system has been developed for the study of both bulk and surface metal oxides by temperature programmed reduction (TPR) under both conventional linear heating and constant rate thermal analysis (CRTA) conditions. It is shown that constant rate temperature-programmed reduction (CR-TPR) is capable of producing higher resolution of overlapping events, provides more insight into reduction mechanisms, and allows easier quantification of reduction processes than conventional TPR. The CR-TPR curves for both bulk and supported copper oxides confirmed that reduction followed a nucleation or autocatalytic mechanism. Bulk nickel oxide was found to reduce via a similar mechanism. Advantages of the CR-TPR “rate-jump” technique to determine reaction energetics are illustrated by investigation of the apparent activation energy (Ea) of CuO reduction, and the results are compared with those obtained under linear heating conditions. Both approaches yield reasonable values of Ea under the appropriate experimental cond...