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Enhancing the accessibility to basic sites of as-synthesized silicas applied in catalytic transesterification

Zapelini, Iago W.; Silva, Laura L.; Oliveira, Cristiano L. P.; Cardoso, Dilson

Applied Surface Science, 2020, vol 507pp. 145159

DOI:10.1016/j.apsusc.2019.145159

Abstract

Heterogeneous catalysis for biodiesel production is a current challenge due to the low activity of solid catalysts, especially caused by diffusional resistances. Hybrid silicas, containing SiO?CTA+ provide high conversions in the transesterification of oils and model molecules, but this activity is limited to the external surface area. The generation of surface roughness in the silica particles can increase the external area of the catalysts and expose the catalytic sites. Rough silicas containing cetyltrimethylammonium (CTA+) surfactant were prepared using different [CTABr]/[TEOS] molar ratios in a biphasic system formed by diethyl ether and water. The resulting solids were characterized by FTIR, O1s XPS, TG, SEM, and TEM. These materials were applied as basic catalysts in a model transesterification reaction representing the formation of biodiesel. Increasing the CTA+ content in the synthesis resulted in higher turnover frequencies, due to the smaller particle size and greater surface roughness of the material, which enhanced the accessibility of reagents to the basic siloxy sites.

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