Acid properties of SiMCM-41 mesoporous molecular sieve

The SiMCM-41 mesoporous molecular sieve was synthesised by the hydrothermal method. The physicochemical characterisation by infrared spectroscopy, X-ray diffraction and thermogravimetry, showed that the material presents a well-defined structure. In this study, the determination of the total acidity and relative strength of the acid sites of the SiMCM-41, was performed by desorption of adsorbed n-butylamine combined with thermogravimetric measurements. The total acidity, determined by means of the amount of amine desorbed normalised by mass of solid, was equivalent to 0.927 mmol g(-1), in the temperature range from 96 to 235 degrees C. By using the Flynn and Wall integral kinetic model, at 5, 10 and 20 degrees C min(-1) heating rates, it was determined that the activation energy to desorb n-butylamine was 90.7 kJ mol(-1), in the same temperature range, evidencing that SiMCM-41 presents only weak acid sites on its surface.