Catalytic oxidation of toluene by ozone over alumina supported manganese oxides: Effect of catalyst loading

This paper investigates effect of manganese loading on total oxidation of toluene by ozone using alumina-supported manganese oxide catalysts. Activities of four loadings of Mn (1, 5, 10 and 20%) were studied in the temperature range of 22–100 °C. Catalysts were characterized by BET, X-ray diffraction (XRD), X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). All catalysts became deactivated at room temperature and their activities were improved by increase of temperature. CHNS and Fourier transform infra red (FT-IR) spectroscopy were used to study catalyst deactivation at room temperature. Alcohols and carboxylic acids were identified as deposited species on the catalysts responsible for catalyst deactivation. A direct relationship between Mn loading and average oxidation state of manganese was found. Catalysts at lower loadings up to 10% were mostly composed of Mn2O3 while a mixture of MnO2 and Mn2O3 were present in catalysts with loadings higher than 10%. It was observed that lower Mn loadings have higher activity in oxidation of toluene. It was proposed that lower oxidation states of manganese are more favorable in decomposition of ozone resulting in higher rate of toluene oxidation.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Oxidation state of Mn depends on loading of Mn on γ-alumina. ► Mn2O3 is formed at Mn loading lower than 10% while MnO2 is dominant MnOx phase at higher loadings. ► Lower oxidation states of Mn in catalysts with lower Mn loading lead to higher rate of toluene oxidation by ozone.