Methanol oxidation using ozone on titania-supported vanadia catalyst.

ABSTRACT

Ozone-enhanced catalytic oxidation of methanol has been conducted at mild temperatures of 100-250 degrees C using a V2O5/ TiO2 catalyst prepared by the sol-gel method. The catalyst was characterized using XRD, surface area measurements, and temperature-programmed desorption of methanol. The oxidation of methanol with ozone in the absence of a catalyst gave about 30% conversion at 100 degrees C. Methanol oxidation over a V2O5/TiO2 catalyst at 100 degrees C gave very little conversion with oxygen, whereas the conversion increased to 80% with ozone. Methanol, having an inlet stream concentration of 15 000 ppmv, can be completely oxidized to CO(x) with an ozone-to-methanol ratio of 1.2, a temperature of 150 degrees C, and a gas hourly space velocity (GHSV) of 60 000 h(-1). The apparent activation energy with ozone was calculated to be ca. 40 kJ/mol, which is much lower than that calculated with oxygen (60 kJ/mol). At low methanol conversion methyl formate was the main product, whereas higher conversions favored oxidation to CO(x). The results imply a consecutive reaction of adsorbed methanol species, favoring selectivity toward methyl formate at lower temperatures and ozone-to-methanol ratios and CO(x) at higher temperatures and ozone-to-methanol ratios. Langmuir-Hinshelwood kinetics was used to model the reaction with and without ozone in the feed. The model parameters were obtained using least-squares fit to a selected set of experimental data, and the model was subsequently compared to all experimental data obtained in this study.