Zeolitic acidity as a promoter for the catalytic oxidation of toluene over MnOx/HZSM-5 catalysts

Series of 10% MnO x /HZSM-5 catalysts with different zeolitic Si/Al ratios were prepared by an incipient impregnation method and evaluated for the catalytic oxidation of toluene. Characterization results indicated that all catalysts exhibited similar textural and redox properties but variable surface acidity. Catalytic testing results showed that the catalytic activities over these catalysts followed a descending order of 10% MnO x /HZSM-5-25 > 10% MnO x /HZSM-5-50 > 10% MnO x /HZSM-5-75, where 10% MnO x /HZSM-5-25 exhibited the optimum catalytic activity and excellent catalytic durability under dry condition and good water-resistant ability under humid condition. A good linear relationship between the toluene conversion efficiency (TOF Mn ) and the total acidity over MnO x /HZSM-5 catalysts was obtained, which revealed the crucial role and promotional effect of zeolitic acidity acting as a promoter on the catalytic activity for toluene oxidation.