Nanocatalysts for sustainable biodiesel production: Reaction parameters, catalyst performance, and future prospects

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The depletion of fossil fuel supplies and growing environmental concerns have accelerated the hunt for sustainable alternatives, such as biodiesel produced through the transesterification process. Even though biodiesel is renewable, biodegradable and environmentally friendly, conventional catalysts used in transesterification often result in low catalytic efficiency, difficult recovery, limited reusability, soap formation and high-energy requirement. The present review critically evaluates the role of nanocatalysts in overcoming these encounters, highlighting on the influence of particle size, surface functionalization, morphology, catalyst stability and reaction conditions in biodiesel production. It covers recent literature analysis which specifies that nanocatalysts significantly improve biodiesel synthesis owing to the particle size ranging from10-100 nm and an increased surface-to-volume ratio of 50-300 m 2 g −1 as compared to (<50 m 2 g −1 ) from conventional catalysts size. This research reviews the methods in the synthesis of nanocatalysts, comparative analysis of nanocatalysts, catalytic performance in biodiesel production and effects on reaction parameters. It compares data from different papers and experiments in order to show the reaction kinetics that provide the best yield and energy efficiency. The review also deliberates on how metal oxide maintains yields above 90% in terms of performance in comparison to, magnetic, supported, bifunctional, immobilized enzymes and carbon-based nanocatalysts. It further outlines the number of cycles (>3) the nanocatalysts can achieve because of the morphology and surface functionalization of the catalysts. Results show high biodiesel conversion from 90-99% under optimised relative conditions of ( 45- 65°C , 1-3 h , 2-6 wt% catalyst loading, and oil-to-methanol ratio of 1:6 -1:15) and > 5 reusability cycles using nanocatalysts . This biodiesel yield is compared to conventional heterogeneous catalyst recording even below 90% yield, with longer reaction time of 3 h, high reaction temperatures up to 80°C and high catalyst loadings above 6 wt% and low reusability (<2 cycles). Despite these advantages, highlights pose emerging challenges including nanoparticle agglomeration, which lowers the reactive surface area by 20-60%, with biodiesel yield losses of 5-20% depending on catalyst composition and reaction conditions. Issues of catalyst leaching, high synthesis costs, scalability constraints and environmental concerns continue to limit commercial application. This review opens a gap for future perspectives to focus on development of hybrid nanocatalyst systems using cost-effective synthesis routes to enhance stability and reusability.