Cobalt-Carbon Catalysts In Confined Nano-Space/Matrix For Aqueous Hydrogenation Of Levulinic Acid

Hydrogenation of levulinic acid?LA?in aqueous phase to?-valerolactone?GVL?is a key step of biomass conversion.Replacement of the precious metal catalyst by cobalt catalysts is important for commercialized application,but the cobalt catalysts are unstable in the aqueous phase reaction.This paper adopts a series of methods such as carbon coating,surface modification of carbon support and nitrogen-doped hollow porous carbon confinement to build a suitable microenvironment at the interface between the support and metallic cobalt,which improves the stability of the catalysts in the aqueous phase reaction.The main conclusions are as follows:?1?We investigated the effect of different solvents on the conversion of levulinic acid to?-valerolactone with Co/Si O₂ catalyst.It was found that water as the solvent GVL has the highest selectivity and low activity.The effect of water on the catalytic hydrogenation reaction of cobalt catalysts was investigated by adding water to pure isopropanol solvent.The introduction of water is detrimental to the reaction process and reduces the hydrogenation activity of the cobalt catalyst,but promotes the formation of the product GVL.?2?A series of Co M/Si O₂ bimetallic catalysts were prepared by the impregnation method.The results show that the introduction of ruthenium can significantly improve the aqueous hydrogenation activity of cobalt catalysts.Moreover,we prepared a catalyst with carbon coating by pyrolyzing the tannic acid and cobalt-ruthenium precursor complexes supported on a silica support?Co Ru@x C/Si O₂?.The surface carbon layer improves the oxidation resistance of metal cobalt in the water phase,reduces the leaching of cobalt,and significantly improves the hydrogenation stability of levulinic acid in aqueous phase.?3?The surface structure of carbon nanotubes was controlled by nitric acid oxidation and high temperature heat treatment.The effects of the surface oxygen-containing groups and defects of carbon nanotubes on the hydrogenation activity and stability of cobalt catalysts in aqueous phase were studied.The conversion rates of Co Ru/CNTs-O and Co Ru/D-CNTs were twice as that of Co Ru/CNTs?untreated?.The method of auxiliary heat treatment can further enhance the interaction between the active component and the support,thereby improving its stability.Co Ru/CNTs-O showed very excellent hydrothermal stability after heat treatment at 700?.?4?On the basis of the ZIF-8 material,we obtained the composite material of ZIF-8@tannis by utilizing the characteristics of polyphenolic hydroxyl groups on tannic acid that are easy to crosslink and polymerize.After pyrolysis,NHPC?nitrogen-doped hollow porous carbon?carbon materials with different inner and outer layer structures were obtained.The performance of Co Ru/NHPC catalyst in aqueous hydrogenation of levulinic acid was studied.The existence of the hollow structure makes it have stronger resistance to metal leaching,and shows excellent stability in the aqueous hydrogenation of levulinic acid.