Isothermal reduction of V2O5 powder using H2 as oxygen carrier: Thermodynamic evaluation, reaction sequence, and kinetic analysis

Abstract

V2O3 was prepared by reducing V2O5 powder using H2 as the oxygen carrier. To initially determine reasonable experimental for the H2-based reduction, oxygen potential and equilibrium calculations were performed. The reaction sequence of the V2O5 powder reduction was predicted by VO phase diagram assessments and was then verified by XRD and XPS measurements under various experimental condition. It was observed that the reduction followed the path of V2O5-VnO2n+1(n = 3 and 6)-VO2-VnO2n-1(n = 7, 6, 5, 4, and 3)-V2O3. Isothermal reduction experiments and kinetic analysis were performed using thermogravimetric analysis (TGA) at 813 K, 823 K, and 833 K, under a pure H2 gas flow. The entire reduction process, from V2O5 to V2O3, obeyed the unreacted shrinking core model (with random instant nucleation and three-dimensional growth of nuclei) and was controlled by chemical reactions. Mathematical fitting showed that the reduction process could be described as G(α) = [−ln(1-α)]1/3, and the apparent activation energy was determined to be 47.11 kJ·mol−1.