On the understanding of the remarkable activity of template-containing mesoporous molecular sieves in the transesterification of rapeseed oil with ethanol

Abstract

Ordered mesoporous molecular sieves of the M41S family, containing their organic template, were evaluated as-synthesized in a basic catalyzed reaction, the transesterification of rapeseed oil with ethanol. These materials [CTA]Si–MCM-48, [CTA]Si–MCM-50, [CTA]Si–MCM-41 (CTA stands for cetyltrimethylammonium cation), which still possess their organic template occluded in the silica pores, were characterized by calorimetry of CO 2 adsorption. These hybrid catalysts present weak basic sites, with low differential heat of CO 2 adsorption between 70 and 90 kJ mol −1; however, the adsorption phenomena were disclosed to be totally reversible at 30 °C. Surprisingly, these hybrid catalysts were shown to be remarkable catalysts for the transesterification of rapeseed oil with ethanol in mild temperature conditions, 79 °C: a total oil conversion was achieved in 1 h with the [CTA]Si–MCM-48, while in equivalent conditions, one of the most efficient mineral solid base, ZrOCs, gave only a conversion of 65%. ZrOCs is considered as a solid base of higher strength, characterized by the heat of CO 2 adsorption of 130 kJ mol −1; interestingly, the CO 2 adsorption is totally irreversible at 30 °C. The most active material in the hybrid molecular sieves series, [CTA]Si–MCM-48, possesses active sites in intermediate position between physisorption and chemisorption in regard to CO 2 adsorption. This solid is characterized by the presence of the most energetic centers within the hybrid catalysts series with the heat of CO 2 adsorption of 90 kJ mol −1 combined with a complete reversibility of the CO 2 adsorption.