Engineering the Band Gap of a g-C3N4 Catalyst by the Incorporation of Organic Acid for Efficient Biodiesel Production

초록

Interest in the exploration of renewable energy sources is increasing due to energy scarcity and growing environmental concerns. Biodiesel is one of the most potential renewable alternatives to fossil fuels and is commonly manufactured by esterification of refined vegetable oils with heterogeneous acid/base catalysts. In this study, we have systematically investigated various acid-doped graphitic carbon nitride (g-C3N4)-based heterogeneous catalysts for biodiesel production using first-principles calculations. The reaction pathways for catalyzing the esterification of free fatty acids (FFA) over these catalysts were analyzed to achieve the formation of methyl butyrate (biodiesel). The calculated results showed a significant reduction in the kinetic energy barriers (to 0.90 eV and 0.41 eV) in the presence of acid-doped (OH and Al-OH) g-C3N4 catalysts, in contrast to the kinetically unfavorable esterification process using the commercial Amberlyst-15 catalyst. Additionally, the enhanced product selectivity was achieved by the Al-OH-doped g-C3N4 catalyst, attributed to strong orbital hybridization between the O-2p orbitals of the potential-determining intermediate and the Al-3p orbital of the acid catalyst in the VB region. In addition, the greater electron density redistribution between the stable tetrahedral intermediate (TS) and Al-OH-doped g-C3N4 catalysts demonstrated an improvement in the kinetics of the esterification reaction. This study emphasizes the importance of incorporating organic acid dopants into g-C3N4 catalysts, revealing their significant impact on the electronic structure and reaction barriers during the esterification process. The present findings open up new perspectives for the design of superior heterogeneous catalysts for efficient biodiesel production application.

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