Effect of noble metals on activity of MnOx/gamma-alumina catalyst in catalytic zonation of toluene

This work addresses effect of addition of two noble metals, platinum or palladium (1 wt.%), on performance of alumina-supported manganese oxides (10 wt.%) in catalytic ozonation of toluene in the range of 22-100 degrees C. Catalysts were characterized by ICP-MS, BET, X-ray diffraction (XRD), hydrogen temperature programmed reduction (H-2-TPR) and X-ray absorption spectroscopy ((AS) including quantitative X-ray absorption near edge structure (XANES) and qualitative extended X-ray absorption fine structure (EXAFS). It was found that addition of platinum improves activity of manganese oxides leading to complete conversion of toluene at 70 degrees C. Palladium was found to be ineffective in enhancing activity of manganese oxides mainly because of lack of atomic interaction between Pd and Mn. Pt and Mn XANES and EXAFS spectra changed after addition of Pt to manganese oxides implying an atomic interaction between platinum and manganese oxides. It is proposed that the interaction between Pt and Mn occurs via surface oxygen of manganese oxide clusters increasing dispersion of Pt atoms in the presence of Mn. This interaction could increase electron occupancy of Mn 3d orbital which is more favorable in decomposition of ozone and consequently oxidation of toluene. (C) 2012 Elsevier B.V. All rights reserved.