Manganese oxide-based catalysts for toluene oxidation

Four different catalysts based on manganese oxide were prepared: a perovskite (LaMnO3), via sol-gelmethod; Mn2O3, rapid method and an Octahedral Molecular Sieve (OMS-2) by two different preparationmethods, via solid state (OMSs) and hydrothermal method (OMSh). The physicochemical properties ofthese catalysts were characterized by X-ray diffraction (XRD), N2adsorption-desorption at -196oC, ther-mogravimetric and differential thermal analysis (TGA/DTA), inductively coupled plasma optical emissionspectroscopy (ICP-OES) and temperature-programmed reduction with hydrogen (H2-TPR). Their catalyticperformances were evaluated in the catalytic oxidation of toluene. Three consecutive catalytic cycles wereperformed for each catalyst in order to reach steady state performances. In order to assess the stability ofthe catalysts under reaction conditions, the catalytic performances were studied upon long term experi-ments running for 24 h at 25% of toluene conversion. For comparison purposes, the catalytic activity of thepresent manganese oxide catalysts was compared with that of typical industrial catalysts such as a com-mercial Pd/Al2O3catalyst containing 0.78% Pd. The crystalline features detected in the XRD patterns, arewell-consistent with the formation of the desired structures. Based on their specific surface area and theirlow-temperature reducibility, the catalysts were ranked as follows: OMSs> Mn2O3> OMSh> LaMnO3. Thistrend was in good agreement with the performances observed in the catalytic removal of toluene. A kineticmodel was proposed and a good agreement was obtained upon fitting with the experimental data.