Biopolymer-templated aluminum catalysts with high activity and stability for biodiesel synthesis

In this study, the role of biopolymer nature was investigated in the synthesis and catalytic performance of aluminum-based heterogeneous catalysts for biodiesel production. Six biomass/biopolymers were evaluated: pectin, chitin, chitosan, cellulose, starch, and shrimp exoskeleton. Regarding the catalytic activity, all materials showed high fatty acid methyl ester (FAME) conversion except the shrimp-exoskeleton catalyst, whose decalcification produced amorphous phases associated with its poor performance. Among all candidates, pectin and chitin catalysts (AlPec and AlCht) displayed the best activity, reaching up to 96% FAME yield in 1 h at only 1 wt% of catalyst loading. Both catalysts exhibited high stability, retaining 70% (AlPec) and 60% (AlCht) of their initial activity after five reuse cycles. GC–MS confirmed that the biodiesel composition remained unchanged, matching conventional biodiesel. Structural analyses revealed that high activity correlated with the formation of crystalline β-NaAlO₂ phases and the presence of medium/strong basic sites, whereas low performance was linked to amorphous phases and predominance of weak basic sites. The results suggestt hat the chemical nature of the biopolymer directs aluminum phase formation, which in turn dominates catalytic activity. This work provides a promising route for designing efficient biopolymer-templated catalysts for biodiesel production.