Removal of toluene using ozone at room temperature over mesoporous Mn/Al2O3 catalysts.

ABSTRACT

The catalytic oxidation of toluene with ozone at room temperature was carried out over hierarchically ordered mesoporous catalysts (CeO2 (meso), Mn2O3 (meso), ZrO2 (meso), and γ-Al2O3 (meso)) and Al2O3 with various textural properties and phases (γ-Al2O3 (meso), γ-Al2O3 (13 nm), and α-Al2O3) to examine the effects of the nature of the catalyst on the catalytic activity. The catalysts were characterized by N2-physisorption measurements, powder X-ray diffraction, temperature programmed reduction, X-ray photoelectron spectroscopy and scanning transmission electron microscopy with energy dispersive spectroscopy. Among the ordered mesoporous catalysts, γ-Al2O3 (meso) had the highest toluene removal efficiency because of its highest surface area and pore volume, which in turn was selected for further investigation. Manganese (Mn) was introduced to various Al2O3 to improve the toluene removal efficiency. Comparing the Mn-loaded catalysts supported on various Al2O3 with different crystalline phases or pore structures, Mn/γ-Al2O3 (meso), had the highest catalytic activity as well as the highest CO2/CO ratio. The higher activity was attributed to the larger surface area, weaker interaction between Mn and Al2O3, and larger portion of Mn2O3 phase. The increase in ozone concentration led to an improvement in the carbon balance but this enhancement was insufficient due to the deposition of by-products on the catalyst. After long term tests at room temperature, the reaction intermediates and carbonaceous deposits of the used catalysts were identified.