On the Effects of Crystalline Planes and Purities on Working States of Vanadium Oxide Catalysts in CO-oxidation

It was confirmed that the kinetics of CO-oxidation over powdered V2O5 under the condition of (PCO⁄PO2) more than 2 differed clearly from that under the (PCO⁄PO2) less than 2 at 450 °C. The activation energies were 5.6 kcal/mol at 250–410 °C and 13 kcal/mol at 410–490 °C under a reductive condition of (PCO⁄PO2)=4.4, and on the other hand 5.9 kcal/mol at 250–490 °C under an oxidative condition of (PCO⁄PO2)=0.43. On a thin crystalline sample, in which the (010) plane was exposed extensively to the surface, a very rapid process appeared at the initial stage but was soon followed by a steady process. The rapid process was explained well by the Elovich law. On the thin crystalline, cautiously purified, the Elovich process did not appear, but the initial rapid process was kept steadily for 10–20 min and then followed by the other steady process. Accompanied by the change in the kinetics during the reaction, the activation energy changed from 2.3 kcal/mol at 271–410 °C and 17 kcal/mol at 410–480 °C to 29 kcal/mol at 271–480 °C under the (PCO⁄PO2)=2.1. Based on these results, the effects of the crystalline planes and the purities on the working states of V2O5 crystal in CO-oxidation are discussed.