Fly ash supported vanadia catalyst: An efficient catalyst for vapor phase partial oxidation of toluene in a micro-reactor

Synthesis of a highly active solid oxidative catalyst has been reported by loading of vanadium on mechanically activated fly ash through wet impregnation method. The catalytic activity of prepared catalyst was measured by gas phase, solvent free selective oxidation of toluene using molecular oxygen as oxidant in a vapor phase micro-reactor under normal atmospheric pressure. The effects of vanadium weight fractions (3, 8 and 15 wt.%) and reaction temperature (453–553 K) on catalytic activity were investigated. The prepared catalysts were characterized by XRF, BET surface area analyzer, XRD, FTIR, pyridine adsorbed FTIR, Diffuse reflectance UV–vis and SEM techniques. Monolayer vanadia species (monomeric and polymeric) are responsible for the catalytic activity and selectivity of benzaldehyde and benzoic acid. Therefore, an increase of the vanadium concentration in the catalysts above the monolayer coverage results in the decrease of conversion and selectivity in toluene oxidation due to the partial blockage of active monolayer species by crystalline V2O5 species. The specific surface area, surface roughness and activity of fly ash were increased by mechanical activation which is being used as an effective support comparable to other silica materials. Thus the overall process is a novel, efficient and promising pathway of cost effective heterogeneous oxidations.