Effective toluene oxidation under ozone over mesoporous MnO_x/γ-Al₂O₃ catalyst prepared by solvent deficient method: Effect of Mn precursors on catalytic activity

In this study, the role of manganese precursors in mesoporous (meso) MnOx/γ-Al₂O₃ catalysts was examined systematically for toluene oxidation under ozone at ambient temperature (20 °C). The meso MnOx/γ-Al₂O₃ catalysts developed with Mn(CH₃COO)₂, MnCl₂, Mn(NO₃)₂.4H₂O and MnSO₄ were prepared by an innovative single step solvent-deficient method (SDM); the catalysts were labeled as MnO_x/Al₂O₃(A), MnO_x/Al₂O₃(C), MnO_x/Al₂O₃(N), and MnOx/Al₂O₃(S), respectively. Among all, MnO_x/Al₂O₃(C) showed superior performance both in toluene removal (95%) as well as ozone decomposition (88%) followed by acetate, nitrate and sulphated precursor MnO_x/Al₂O₃. The superior performance of MnO_x/Al₂O₃(C) in the oxidation of toluene to CO_x is associated with the ozone decomposition over highly dispersed MnO_x in which extremely active oxygen radicals (O²⁻, O₂²⁻ and O⁻) are generated to enhance the oxidation ability of the catalysts greatly. In addition, toluene adsorption over acid support played a vital role in this reaction. Hence, the properties such as optimum Mn³⁺/Mn⁴⁺ ratio, acidic sites, and smaller particle size (≤2 nm) examined by XPS, TPD of NH₃, and TEM results are playing vital role in the present study. In summary, the MnO_x/Al₂O₃ (C) catalyst has great potential in environmental applications particularly for the elimination of volatile organic compounds with low loading of manganese developed by SDM.