MoO3/ZnMoO4 Composite Obtained in a One-Pot Reaction and Applied in the Production of Biodiesel from Acid Feedstocks

Abstract Despite being widely recognized within the scientific community, the synthesis of biodiesel from acidic feedstocks remains challenging. In this work, a heterogeneous catalyst comprising molybdenum trioxide and zinc molybdate (MoO3/ZnMoO4) was synthesized via the modified Pechini method and characterized to assess its structural, morphological, and chemical properties. The catalytic performance of MoO3/ZnMoO4 in esterification, transesterification, and simultaneous esterification-transesterification reactions (SET) at different temperatures and times of reaction was evaluated. α-MoO3 and ZnMoO4, with high crystallinity, were obtained, exhibiting Lewis acid sites and a negatively charged surface across all pH values. Heterogeneous morphology identified by SEM/EDS, including ribbon-like and prismatic particles characteristic of α-MoO3, alongside irregular micrometric particles attributed to the ZnMoO4 phase. The composite exhibited strong catalytic activity in transesterification, achieving conversion of 76.61% at 160 °C/120 min and 82.84% at 200 °C/120 min─both exceeding values reported for pristine ZnMoO4. In esterification, conversions ranged around 96% and 97%, with limited dependence on temperature and reaction time, suggesting that milder conditions are sufficient for high efficiency. In the SET reaction, conversions of about 90% were obtained using oil acidified with 10% or 20% oleic acid, and 96.22% conversion was achieved with crude palm oil, demonstrating strong tolerance toward acidic feedstocks. Moreover, the material kept its catalytic activity after 4 reuse tests. The superior performance of the composite is primarily attributed to the synergistic interaction between ZnMoO4 and MoO3.