Effect of Fe/Mn Ratio on the Catalytic Oxidation of Toluene over Porous γ-Al₂O₃ Supported Fe and Mn Bimetal Catalysts

Reflux-coprecipitation method is used to synthesize porous γ-Al₂O₃ supported Fe and Mn bimetal catalysts, and then the as-obtained porous Fe_xMn_y/Al₂O₃ with different Fe/Mn ratio are measured by BET, XRD, SEM, TEM, XPS, and H₂-TPR. Meanwhile, effects of Fe/Mn ratio on the adsorption and catalytic oxidation properties of toluene by the as-obtained porous Fe_xMn_y/Al₂O₃ are experimentally studied in a micro fixed-bed reactor, and then the structure–activity relationship of the porous Fe_xMn_y/Al₂O₃ catalysts for toluene removal are obtained. Finally, the adsorption and oxidation mechanism of toluene over these porous Fe_xMn_y/Al₂O₃ is proposed based on the in-situ FTIR analysis. Results indicate the Fe/Mn ratio has a significantly influence on the toluene oxidation activity of the porous Fe_xMn_y/Al₂O₃ catalysts, among which porous Fe₁Mn₂/γ-Al₂O₃ exhibits the highest toluene conversion with T₉₀ of 238 °C as well as the lowest activation energy of 32.68 kJ/mol under WHSV of 80,000 mL/g^/h. However, the porous Fe₁Mn₂/γ-Al₂O₃ with different Fe/Mn ratios exhibit similar toluene adsorption capacities, and the Bangham model is well fitted with toluene adsorption over all these porous Fe_xMn_y/Al₂O₃. In situ FTIR results reveal that adsorbed oxygen and lattice oxygen simultaneously react with the adsorbed toluene, which results in promoting the oxidation of methyl in toluene and facilitating the breakage of aromatic C = C to form CO₂.