Catalytic oxidation of toluene over binary mixtures of copper, manganese and cerium oxides supported on γ-Al2O3

The catalytic oxidation of toluene has been investigated over binary mixtures of copper, manganese and cerium oxides supported on high surface area γ-Al2O3 in comparison with the corresponding single metal oxide components. Catalysts were synthesized with the impregnation method and were characterized with respect to their specific surface area (BET method), phase composition and mean crystallite size (XRD technique), reducibility (H2-TPR) and adsorption/desorption characteristics toward toluene (TPD followed by TPO). Results obtained using a feed composition consisting of 1000 ppm toluene in air showed that the catalytic performance of mixed oxide catalysts can be improved significantly by proper selection of metal oxide (MxOy) loading and composition. The intrinsic activity of optimized catalysts, measured under differential reaction conditions, was found to be significantly higher compared to that of their single-component counterparts. This has been attributed to the better dispersion of the active MxOy phases, their increased reducibility (reactivity of surface oxygen), and their lower tendency to form coke deposits under reaction conditions. Addition of a second VOC (propane) or water vapor in the feed affected differently the activity of optimized-mixed oxide catalysts. As a general trend, inhibition by the presence of propane was more pronounced for CeO2-containing samples whereas the presence of H2O affected mainly the CuOx-containing catalysts. It is concluded that the VOC oxidation activity of Al2O3-supported mixed oxide catalysts is determined by the reducibility of the dispersed active phases, which may be controlled by proper selection of MxOy nature, loading and composition.

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► Combustion activity of mixed oxide catalysts depends on MxOy type, loading and composition.
► Activity of optimized catalysts is higher than that of single-component counterparts.
► Enhancement of activity is due to the increased reducibility of active MxOy phases.