Cerium–Impregnated Rice Husk–Derived Catalysts for Fatty Acid Esterification Using Methyl Acetate

Abstract

This study reports the synthesis and characterization of heterogeneous acid catalysts derived from rice husk biochar, modified by sulfonation and Ce(NO₃)₃·6H₂O (cerium (III) nitrate hexahydrate) impregnation, for fatty acid esterification using methyl acetate as a glycerol-free reaction route. The research aims to valorize agricultural residues as renewable and sustainable precursors for solid acid catalysts, reducing the dependence on fossil-based materials and supporting cleaner energy technologies. The sulfonation process effectively introduced Brønsted and Lewis acid sites, whereas cerium incorporation enhanced the structural and acidic properties of the material. Comprehensive physicochemical characterization through XRF, FTIR, BET, and SEM analyses confirmed the successful incorporation of both sulfonic and cerium species and revealed an improvement in surface area, porosity, and active site distribution. Among the synthesized catalysts, the one with 10 wt% Ce exhibited superior catalytic performance, achieving a Fatty Acid Methyl Esters (FAME) content of 85.71 wt% after 6 h of reaction at 240 °C in the esterification of oleic acid. The catalyst also demonstrated good structural stability and reusability over four reaction cycles, with minimal loss of activity. These results highlight the potential of agrowaste–derived materials for developing low–cost and efficient, and reusable acid heterogeneous catalysts, with relevance for glycerol-free FAME production and future biodiesel-related applications.