Tailoring the coordination environment of Co-Sn active sites via zinc aluminate spinel support for highly chemoselective hydrogenation of methyl oleate

The chemoselective hydrogenation of methyl oleate to oleyl alcohol was investigated over Co-Sn catalysts supported on zinc aluminate (ZnAl2O4). The ZA-M support, synthesized via a methanol-mediated solvothermal route, provided a high specific surface area (296.8 m²/g) and an optimized mesoporous structure. Sequential NaBH4 and H2 reduction finely tuned the coordination of active sites, enabling the optimized 2Co4SnBH/ZA-M catalyst to achieve a superior oleyl alcohol yield (33.58%) and a high selectivity (65.39%) at a conversion level of 51.36% via a direct hydrogenation pathway. Based on bulk and surface characterizations, a fraction of cobalt was found to remain in a cationic state, stabilized within a network of interfacial Co-O-Sn complexes and framework CoAl2O4. These species are proposed to function as bifunctional active centers, where the Snⁿ⁺/Sn⁰ species and neighboring Co²⁺ sites cooperatively enhance the chemoselectivity toward C=O reduction. Furthermore, the optimized catalyst demonstrated reasonable structural stability and reusability over four cycles, maintaining its catalytic viability despite a minor extent of metal leaching. These findings underscore the efficacy of spinel-supported ionic-metallic ensembles for the highly chemoselective and efficient hydrogenation of long-chain fatty acid methyl esters.