Low-Temperature Benzene Ozonation over Mn/Y-Zeolites: Structure–Activity Relationships for Environmental Applications

Volatile organic compound (VOC) emissions from industrial sources require efficient low-temperature removal technology. Although catalytic ozonation enables benzene oxidation under mild conditions, the effect of the catalyst support properties remains poorly understood. This study investigates the influence of the SiO2/Al2O3 ratio of Y-type zeolite supports (45–193) on the structure and catalytic performance of manganese oxides for benzene ozonation. Manganese oxide catalysts (5 wt % Mn) were prepared by impregnation on Y-type zeolites with varying SiO2/Al2O3 ratios. The catalyst structures were characterized using X-ray absorption fine structure (XAFS) and H2-temperature-programmed reduction (H2-TPR). The catalytic performance was evaluated at 40–70 °C with 150 ppm benzene and 2250 ppm ozone under both dry and humid (0.4% H2O) conditions. XAFS analysis revealed highly dispersed manganese species with oxidation states varying from +2.6 to +3.0. The catalyst with the SiO2/Al2O3 ratio of 45 achieved the highest benzene conversion (85% at 50 °C) under dry conditions, compared to 65% for that of 193. In situ FTIR and TPO analyses demonstrated that lower SiO2/Al2O3 ratios suppressed intermediate accumulation by 30–40%. Water vapor showed dual effects: enhancing activity for moderate SiO2/Al2O3 ratios (100–150) while inhibiting the hydrophilic Mn/ZY45 catalyst. The SiO2/Al2O3 ratio critically controls both manganese speciation and catalytic performance, with the ratio of 45–100 providing optimal activity through balanced hydrophobicity and minimal intermediate accumulation. These findings enable the rational design of zeolite-supported catalysts for practical VOC abatement.