Recent trends in sustainable biodiesel production using heterogeneous nanocatalysts: Function of supports, promoters, synthesis techniques, reaction mechanism, and kinetics and thermodynamic studies

Abstract

Biodiesel is a biofuel that has several benefits over petroleum diesel. In recent years, the utilization of biodiesel produced from oil-bearing edible biomasses has grown significantly. Although the first choice is edible feedstocks, they will not be sustainable due to the increasing global prices, energy demand, and greenhouse gas emissions. Hence, inedible biomasses are claimed to be potential feedstocks for biodiesel production via catalyzed transesterification. In contrast to homogeneous and heterogeneous catalysts, the nanocatalysts are much favoured owing to their simple separation from the final products and retention of catalytic activity in reuse for consecutive cycles. Hence, nanocatalysts are crucial in biodiesel production due to their efficacious catalytic productivity. In particular, nanocatalysts can be excellent substitutes for conventional catalysts owing to their distinct characteristics including high active surface area, high reusability, better catalytic performance, high biodiesel conversion, and environmental friendliness. Biodiesel production can be enhanced by using non-edible biomasses and nanocatalysts like zirconium oxide (ZrO2), nano CaO, nano CaCO3, titanium-doped zinc oxide, etc. These nanocatalysts are efficacious with an approximately 80–98 wt% biodiesel conversion under optimum operating conditions, indicating that this strategy is a viable route for biodiesel synthesis. This review article extensively discusses the role and significance of advanced nanocatalysts on the biodiesel yield/conversion along with the insights into the reaction mechanism. The function of supports and promoters on the nanocatalytic activity and performance in the biodiesel synthesis is also discussed. To add, renewable feedstocks, synthesis routes, and characterization techniques of nanocatalysts are studied. Moreover, the kinetics and thermodynamic studies together with the effect of kinetic and thermodynamic parameters on the nanocatalyzed transesterification process have been reviewed. Also, this paper entails the process simulation and multi-objective optimization of heterogeneous nanocatalyzed biodiesel production. Finally, this review provides substantial information to researchers in developing and fabricating cost-effective nanocatalysts for the sustainable biodiesel production.