THERMOGRAVIMETRY OF WO3 REDUCTION IN HYDROGEN - KINETIC CHARACTERIZATION OF AUTOCATALYTIC EFFECTS

Chemical and autocatalytic events occurring during the hydrogen-reduction of WO3 were observed and characterized by thermogravimetry, X-ray diffractometry and a kinetic analysis. The results indicated that WO3 is completely reduced to W-degrees near 800-degrees-C, via the formation of WO2.72 (at 520-degrees-C) and WO2 (at 600-degrees-C) as intermediate products. Kinetically, the initial stage of the reduction was found to be dominated by the formation of WO2, and to be influenced by strong autocatalytic effects associated with the commencement of formation of W-degrees. These results fulfil the requirements of a consecutive autocatalytic kinetic model, whereby the dissociative adsorption of H-2 on freshly generated W-degrees surfaces is considered the rate determining step. Arrhenius plot based on the initial rate as a function of temperature data resulted in an activation energy value of 118+/-5 kj mole-1.