Utilization of a PILC-Al obtained from Uruguayan clay as support of mesoporous MnOx-catalysts on the combustion of toluene

Abstract

Catalytic oxidation is considered one of the best methods to remove volatile organic compounds. One of the main advantages of catalytic combustion is the low emissions of minor contaminants released to the atmosphere and low operative cost, followed by high removal properties for pollutants, compared to adsorption and incineration. The purpose of this paper is to review the behaviour of a group of catalysts extracted mainly from the location of Cerro Largo (Bañado de Medina), Uruguay, through evaluation of the total combustion of toluene. The montmorillonite was pillared with a polycation of Al13, with a Keggin-like structure using conditions to ensure a molar ratio OH−/Al3+ of 2 and then the resulting pillared clay was washed, calcined, and used as support of the active catalytic phase. The catalysts contain manganese oxide (as Mn2O3) which was obtained from Mn(CH3COO)2.4H2O. Catalysts were obtained by incipient wetness impregnation method and heated from room temperature to 550 °C, then maintained at this temperature for 4 h in air atmosphere. The resulting catalysts and support were characterized by thermogravimetric analysis, X-ray diffraction, N2-physisorption at 77 K, temperature programmed reduction, elemental analysis, scanning electron microscopy and transmission electron microscopy. The catalytic tests were performed in a fixed bed reactor using 0.5 g of sample, operating at atmospheric pressure and a feed of a mixture consisting of 192 cm3/min of Ar, 8 cm3/min of O2 and 2000 ppmv of toluene. Catalytic tests were carried out using a ramp mode from 200 °C to 500 °C with a heating rate of 1 °C/min. Samples from the reactor outlet stream were taken every 50 min and the reaction products were analyzed by gas chromatography. Based on the results of the X-ray analysis, the manganese found in the catalysts is in the form of Mn2O3. All the catalysts were active, and the gaseous by-products were CO2 and H2O in all cases. The best catalytic performance was obtained with the catalyst containing 40% of Mn2O3 on the pillared clay (90% conversion at 300 °C). No decrease in catalytic activity was observed when analysing the stability test for 24 h. Thus, it is possible to conclude that the catalyst obtained shows good catalytic performance and high stability in the combustion of toluene.