Effect of acidic and red-ox sites over modified ZSM-5 surface on selectivity in oxidation of toluene

The modified HZSM-5 zeolites via alkali-treated with various NaOH aqueous solution and supported iron oxide by impregnation technique was prepared, as proved by XRD, SEM, TEM, XPS, NH3-TPD and ICP-OES to determine their phase structure, composition and surface character. These modified materials were tested for catalyzing solvent-free oxidation of toluene under mild conditions. The experimental results indicated that the alkali-treated HZSM-5 showed higher activity because of reduction of strong acidic sites on the surface. However, the alkali-treated HZSM-5 supported iron material exhibited high selectivity to benzaldehyde via promoting the oxidation of toluene or benzyl alcohol and limiting the further oxidation of benzaldehyde into phenol caused by lowing surface Brönsted acidity and introducing Fe red-ox sites.