Catalytic oxidation of benzene by ozone over manganese oxides supported on USY zeolite

This paper reports the catalytic behavior toward benzene oxidation in the presence of ozone of manganese oxides supported on a high Si/Al ratio zeolite (SiO₂/Al₂O₃ = 180). The catalysts were characterized by N₂ adsorption, X-ray absorption fine structure (XAFS), and temperature-programmed reduction (TPR). By a conventional impregnation technique, the manganese oxides were highly dispersed in the zeolite Y in the 3+ oxidation state, and they were the active sites for benzene oxidation by ozone. Steady-state activities were obtained at 313-373 K under both dry and humid conditions. Under both of those conditions, a strong correlation was observed among the amounts of ozone consumed, benzene oxidized, and COx formed. Water vapor in the reaction gas enhanced benzene oxidation by promoting by-product compound oxidation by the catalyst, and water vapor thus slightly improved CO₂ selectivity. Fourier-transformed infrared (FTIR) and temperature-programmed oxidation (TPO) studies demonstrated that benzene was oxidized on the catalysts to oxygen-containing by-products such as weakly bound formic acid and strongly bound carboxylates. Although formic acid was steadily formed during the reaction, it was readily oxidized to CO ₂ and CO by the ozone feed. The ratio of ozone decomposition to benzene oxidation was approximately 9-10 and was almost independent of reaction temperature and humidity, indicating that ozone was efficiently consumed through benzene oxidation under the reaction conditions.