Magnetically Separable Catalysts for Sustainable Synthesis of Trimethylolpropane Trioleate with Excellent Tribological Performance

To address the challenges in green synthesis and efficient catalyst separation for high-grade polyol ester lubricants, a Fe 3 O 4 –SnO-SiO 2 composite catalyst with high activity, magnetic separability, and cycling stability was designed for efficient esterification of trimethylolpropane trioleate (TMPTO). Characterizations, including XRD, VSM, SEM-EDS, XPS, and BET, confirm that Fe 3 O 4 provides magnetic separation, SnO offers Lewis acid sites, and SiO 2 improves dispersion and structural stability, realizing the integration of efficient catalysis, fast magnetic separation, and stable recycling. At 200 °C for 4 h, the TMPTO conversion reaches 91.3% and remains 87.8% after 5 cycles. The product shows no byproducts and improved structural regularity. Tribological tests exhibit a stable coefficient of friction (0.08–0.10), with wear volume and rate about one-third of the uncatalyzed system, reaching or exceeding commercial products. DFT and FTIR reveal that Sn 2+ acts as the active center to activate oleic acid and reduce the energy barrier. This work provides a new catalyst system and theoretical basis for green industrial production of high-end ester lubricants.