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

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 CO2 adsorption. These hybrid catalysts present weak basic sites, with low differential heat of CO2 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 CO2 adsorption of 130 kJ mol−1; interestingly, the CO2 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 CO2 adsorption. This solid is characterized by the presence of the most energetic centers within the hybrid catalysts series with the heat of CO2 adsorption of 90 kJ mol−1 combined with a complete reversibility of the CO2 adsorption.

Template-containing molecular sieves such as [CTA]Si–MCM-48 were shown to possess very weak basic sites by calorimetry, however the CO2 adsorption isotherms are totally reversible. Their catalytic activities in transesterification are comparable to that of strong inorganic bases.Figure optionsDownload high-quality image (190 K)Download as PowerPoint slide