The Research On The Hydrogenation Of Methyl Levulinate And γ-Valerolactone Over Cobalt-based Catalysts

The utilization of low-cost renewable biomass as a carbon source to produce biofuels,organic intermediates,and platform compounds,etc.,is rapidly developing.γ-valerolactone is one of the most promising platform compounds,and the development of an effective catalytic system for the synthesis and conversion ofγ-valerolactone is the focus of research.The traditional noble metal catalytic system has the shortcomings of high cost,difficult separation,and poor stability,so it is very important to develop a cheap,efficient,and stable non-precious metal catalytic system for the synthesis and conversion ofγ-valerolactone.The main work developed in this paper is as follows.（1）A series of Co/La₂O₃-Nb₂O₅catalysts were prepared by precipitation and impregnation.The catalytic activity was evaluated by the hydrogenation of methyl levulinate.Various characterization techniques were applied to analyze the structure and properties of Co/La₂O₃-Nb₂O₅ and discussed their influences on catalytic activity.10 wt%Co/La₁Nb_0.33 showed the best performance in the hydrogenation of methyl levulinate.Under the optimized conditions（150℃,3 MPa H₂,6 h）,a 97.7%yield ofγ-valerolactone at 98%methyl levulinate conversion was obtained.The superior activity can be attributed to the synergistic effect between the highly dispersed Co⁰nanoparticles and the appropriate amount of basic sites.This Co-based catalyst still maintains high activity after 5 consecutive runs（85%γ-valerolactone yield）.（2）A series of Co/Zr O₂-Nb₂O₅catalysts were prepared by adjusting the molar ratio of Zr OCl₂·8H₂O to Nb（HC₂O₄）₅ and the content of Co（NO₃）₂.Their catalytic activity was evaluated in the synthesis ofγ-valerolactone from methyl levulinate by catalytic transfer hydrogenation reaction.A variety of characterization methods were used to reveal the structure-activity relationship of Co-based catalysts.10Co/Zr₈Nb₂exhibited excellent catalytic activity due to its highly dispersed Co⁰ and Lewis acid sites.The reaction was carried out at 180℃for 2 h using isopropyl alcohol as both solvent and hydrogen donor,and resultantly gave a 99.3%yield ofγ-valerolactone at full methyl levulinate conversion.Notably,the 10Co/Zr₈Nb₂ catalyst exhibited remarkable catalytic stability after 10 consecutive runs（95%γ-valerolactone yield）.（3）The catalytic performance of CoCu/Al₂O₃catalysts was evaluated in synthesizing 2-methyltetrahydrofuran by selective catalytic hydrogenation ofγ-valerolactone.The result showed that the 5Co10Cu/Al₂O₃ catalyst presented the highest catalytic activity.A 98.8%yield of 2-methyltetrahydrofuran at fullγ-valerolactone conversion was obtained under 4.5 MPa H₂ at 200℃,for 6 h.The high activity is due to the synergistic effect between Co and Cu.The catalyst has good stability,and the yield of 2-methyltetrahydrofuran can reach over 90%after being recycled 5 times.In conclusion,the green catalytic process of cobalt-based catalytic preparation ofγ-valerolactone was realized,and the preparation ofγ-valerolactone by isopropanol as both solvent and hydrogen donor was achieved,which solved the self-sufficiency of hydrogen source within the reaction system and completed the catalytic synthesis of2-methyltetrahydrofuran by further hydrogenation ofγ-valerolactone.