Keggin type dilacunary phosphotungstate anchored to different acidic supports: design, characterization and its catalytic evaluation for the synthesis of fuel additives with kinetic study†

This study consists of the synthesis of sustainable heterogeneous catalysts comprising dilacunary phosphotungstate and different acidic supports (zeolite HY and hydrous zirconia) via the incipient wet impregnation method. The catalysts were characterized by various physicochemical techniques and evaluated for solvent-free cleaner synthesis of n-butyl levulinate, a promising biofuel additive, under mild conditions. By undertaking a detailed optimization study, an outstanding selectivity of n-butyl levulinate (≥93%), as well as exceptional turnover numbers (>1300), was achieved. The reaction kinetics and order were investigated for both catalytic systems, revealing adherence to a true chemical step. The effect of the support was studied to compare the activity of the catalysts. The selected best catalyst was regenerated and recycled for multiple runs. Its versatility was explored in the esterification of a range of bio-based molecules into various biofuel additives with remarkable selectivity. Interestingly, it achieved over 90% selectivity for a range of C1–C7 straight-chain alcohols, marking a significant accomplishment. A high-gravity approach and scale-up reactions were also explored to ensure the practical relevance of the findings, emphasizing the potential of the catalyst for broader application.