Cobalt-glycerolates derived Co@C-T catalysts for the catalytic transfer hydrodeoxygenation of lignin-derived vanillin

The hydrodeoxygenation of lignin-derived bio-oil is the key to its upgrading into biofuels. Currently, the catalytic transfer hydrodeoxygenation (CTHDO) has been widely studied due to the avoidance of the use of hydrogen gas. In this work, cobalt-glycerolates nanospheres derived Co@C-T catalysts were synthesized via the solvothermal method, followed by the carbothermic method at different calcination temperatures in a nitrogen atmosphere. The obtained Co@C-450 catalyst exhibited the best vanillin CTHDO performance and afforded nearly 100 % conversion of vanillin and 87 % yield of 2-methoxy-4-methylphenol (MMP) under the conditions of 140 °C, 1 MPa N₂ and 3 h using isopropanol as H-donor. Based on the various characterizations, the Co@C-450 catalyst possessed the appropriate metallic Co⁰ sites, acid sites (Co(II)), and carbon defects, and the high catalytic activity was attributed to the synergistic effects of them. During the CTHDO process, the Co⁰ sites were responsible for carbonyl hydrogenation of vanillin to generate 4-(hydroxymethyl)-2-methoxyphenol (HMP) and the generation of active hydrogen species from isopropanol, while the acid sites (Co(II)) were responsible for the cleavage of the CO bond in HMP to form MMP. In addition, the Co@C-450 catalyst had good applicability to other lignin-derived monomers, and its performance did not decrease after 11 runs. This work could provide some insights for upgrading bio-oil.