Dual-Function Heterogeneous Catalyst PMo11@MIL-101(Cr) for Efficient CO2 Fixation and Sustainable Biodiesel Synthesis

A multifunctional noble-metal-free catalyst, PMo11@MIL-101(Cr), was developed by encapsulating monolacunary phosphomolybdate (PMo11) into the mesoporous MIL-101(Cr) framework across varying loadings, and evaluated for two sustainable catalytic reactions: CO2 cycloaddition with epoxides and esterification of oleic acid. Structural integrity and successful incorporation were confirmed through PXRD, N2 adsorption/desorption, FT-IR, ICP-OES, FE-SEM, and TEM analyses. Among the tested compositions, the 35%PMo11@MIL-101(Cr) catalyst achieved 95% conversion and a turnover frequency (TOF) of 3007 h–1 for CO2 fixation under solvent-free conditions and without any cocatalyst. The catalyst maintained 85% activity over six consecutive cycles, highlighting its durability. For esterification, 20%PMo11@MIL-101(Cr) delivered optimal performance with 80% conversion and a TOF of 263 h–1, retaining 65% activity after 11 cycles. Py-FTIR spectroscopy, used to identify the nature and concentration of surface acid sites, revealed a notable enhancement in total acidity upon incorporation of PMo11, with the composite showing significantly higher acidity compared to pristine MIL-101(Cr). This rise in acidity, correlated with reduced surface area and pore volume, confirms the successful integration of PMo11 and its influence on the material’s acidic character. Notably, the coexistence of Bro̷nsted and Lewis acid sites played a pivotal role in both reactions, facilitating epoxide activation and CO2 insertion, as well as carbonyl protonation and ester formation. Together, these findings establish PMo11@MIL-101(Cr) as a versatile and sustainable catalyst platform for CO2 utilization and biodiesel production, contributing meaningful solutions to global energy and environmental challenges.