(426h) Oxidation of Methanol Using Ozone on Titania-Supported Vanadium Catalyst

Catalytic ozone decomposition of methanol has been conducted at mild temperatures of 100 to 250°C using V2O5/TiO2 catalyst prepared by either sol-gel or wet impregnation methods. The catalysts were characterized using XRD, surface area measurements, and desorption of CH3OH. Gas phase oxidation of methanol with ozone in the absence of a catalyst gave about 30 % conversion at 100 oC. Methanol oxidation over 10 wt% V2O5/TiO2 at 100 oC gave very little conversion with oxygen whereas the conversion increased to 80 % with ozone. Methanol having inlet stream concentration of 15,000 ppmv can be completely oxidized to CO2, with ozone-to-methanol ratio of 0.6, temperature of 200 oC and GHSV of 37,500 h-1. The apparent activation energy with ozone (8.8 kJ/mol) which is much lower than that with oxygen 68 kJ/mol. Temperature program desorption studies of methanol from the V-Ti surface are used to confirm increased catalyst activity above 150 oC. The effects associated with the operating variables of the flow reactor were explained using a mechanistic model which implies that the consecutive reaction adsorbed methanol species and adsorbed atomic oxygen species initiate the formation of HCHO, then to HCOOCH3 and finally to CO2. Decomposition of ozone on catalyst surface provides the active oxygen species (O2-), which allow the oxidation to proceed at lower temperatures, compare to molecular oxygen. Retention time studies showed that reaction proceeds through surface methoxy species formation, producing large amounts of methyl formate at lower temperatures and reaction proceeds to CO2 with increased conversion of methanol. Ozone appears to help in preserving the catalyst active sites at relatively low temperature. Langmuir-Henshilwood expression was used to develop a steady-state kinetics of the oxidation of methanol.