Activation energies of the reduction of bulk and supported vanadium pentoxide

Abstract

Three methods to evaluate apparent activation energies for reduction from temperature-programmed reduction (TPR) measurements are discussed. Application of the well known method of Gentry results in values of the experimental activation energy, E_e, which are dependent on the heating rate in the region 8–15 K min^–1. Two new approaches are described: the reference method and the curve-fitting method.

Application of a curve-fitting method, by integration of an appropriate nucleation equation, results in an activation energy for the growth of nuclei, E_a, of 60 ± 3 kJ mol^–1 for both bulk and supported V₂O₅.

In the reference method, the onset of a single TPR peak of a sample under investigation is compared to the onset of the TPR peak of a reference sample with a known value of E_e. Activation energies obtained by the reference method are in good agreement for almost all heating rates applied (8–20 K min^–1). Agreement with the activation energy obtained by Gentry's method exists only in a limited region of heating rates.