A novel solid base catalyst for transesterification of triglycerides toward biodiesel production: Carbon nanohorn dispersed with calcium ferrite

Carbon nanohorn (CNH) dispersed with a calcium ferrite Ca2Fe2O5 (Ca2Fe2O5-CNH) was synthesized as a new catalyst, and its superior catalytic activity to convert a triglyceride to a fatty acid methyl ester via transesterification reaction was demonstrated. The process to prepare this catalyst has three steps as follows. For the first step, Fe-dispersed CNH (Fe-CNH) was synthesized by a gas-injected arc-in-water method. For the second step, the oxidation treatment in diluted CO2 or in air was performed on Fe-CNH to transform Fe nanoparticles dispersed in Fe-CNH to Fe3O4 or Fe2O3, respectively. For third step, Fe3O4-dispersed CNH (Fe3O4-CNH) or Fe2O3-dispersed CNH (Fe2O3-CNH) was co-calcined with Ca (NO3)(2), resulting to the formation of Ca2Fe2O5-CNH. The powdery catalysts of Ca2Fe2O5-CNH can be recovered by magnetic field for recycled use. In the transesterification experiment, tricaprylin was converted to methyl caprylate. The reaction rate of this transesterification using Ca2Fe2O5-CNH catalysts was obviously higher than using conventional CaO catalyst. Also CNH supporting CaO without including Fe (CaO-CNH) was prepared, and this catalyst exhibited a high catalytic activity for this transesterification. However, CaO-CNH did not have the property for magnetic recovery. Among the catalysts prepared here, Ca2Fe2O5-CNH prepared using Fe3O4-CNH as precursor exhibited the highest reaction rate for the transesterification. The hybridization of the calcium ferrite possessing basic sites with hydrophobic CNH was considered to be the key factor for its high catalytic performance. (C) 2016 Elsevier B.V. All rights reserved.