Effective toluene oxidation under ozone over mesoporous MnOx/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/gamma-Al2O3 catalysts was examined systematically for toluene oxidation under ozone at ambient temperature (20 degrees C). The meso MnOx/gamma-Al2O3 catalysts developed with Mn(CH3COO)(2), MnCl2, Mn(NO3)(2.4)H2O and MnSO4 were prepared by an innovative single step solvent-deficient method (SDM); the catalysts were labeled as MnOx/Al2O3(A), MnOx/Al2O3(C), MnOx/Al2O3(N), and MnOx/Al2O3(S), respectively. Among all, MnOx/Al2O3(C) showed superior performance both in toluene removal (95%) as well as ozone decomposition (88%) followed by acetate, nitrate and sulphated precursor MnOx/Al2O3. The superior performance of MnOx/Al2O3(C) in the oxidation of toluene to COx is associated with the ozone decomposition over highly dispersed MnOx in which extremely active oxygen radicals (O2-, O-2 (2-) 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 MnOx/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.

Automated summary

The study systematically examined the role of manganese precursors in mesoporous MnOx/gamma-Al2O3 catalysts for toluene oxidation under ozone at ambient temperature, with MnOx/Al2O3(C) showing superior performance in toluene removal and ozone decomposition. The superior performance of MnOx/Al2O3(C) is attributed to the highly dispersed MnOx facilitating ozone decomposition and the vital role of toluene adsorption over the acid support. The study highlights the importance of properties such as Mn3+/Mn4+ ratio, acidic sites, and particle size in the catalytic performance.