Ceramic honeycomb monoliths were washcoated with cryptomelane-type manganese oxides and their catalytic performance was evaluated in the oxidation of ethyl acetate. The effect of a mixture of ethyl acetate with toluene and of the presence of water vapour was also assessed.Different coating parameters, namely size of catalyst particles, number of immersions in the washcoating solution, presence of an initial coating with alumina, calcination temperature of this coating, as well as the amount of binding agent and ethanol in the washcoating solution were studied and optimized based on the catalytic activity of the structured catalyst. Small particles are required for a correct impregnation; however, since the smallest particles are less active, an intermediate size achieved the best catalytic results. Increasing the number of immersions over 3 did not significantly increase the catalytic activity of the structured catalyst. The presence of an initial coating with alumina and a binding agent (colloidal alumina) in the washcoating solution was found essential to increase the activity, whereas increasing the calcination temperature after the initial alumina coating above 500°C decreased the activity of the catalyst. The presence of ethanol in the washcoating solution did not significantly improve the activity of the structured catalyst.The optimized structured catalyst presented high catalytic activity in the removal of ethyl acetate (90% conversion into CO2 at 256°C) and high stability during 100 h of reaction. The addition of toluene or water vapour in the feed gas did not significantly affect the activity of the coated monolith.
Keywords: Low-temperature catalytic oxidation; ceramic monolith; ethyl acetate; manganese oxides; volatile organic compounds.