Preparation Of HZSM-5 Supported Fe-Pd Bimetallic Catalyst And Its Application In Hydrogenolysis Of Lignin

Lignin is a biomass resource with rich aromatic structure in earth.Catalytic conversion of lignin into high-value fine chemicals and fuels is of great significance for solving the energy shortage and environmental pollution to achieve global sustainable development.However,the efficiency of lignin depolymerization and the yield of aromatic monomers are still low due to the complex and stable structure of lignin.Therefore,developing an efficient way to depolymerize lignin with high yield of aromatic monomers remains one of the most important topics to the scientific world.In this work,monometallic Fe/HZSM-5 and Pd/HZSM-5 and bimetallic Fe-Pd/HZSM-5catalyst were prepared by using impregnation method.The effects of Fe content?5.0wt%¹5.0 wt%?,Pd content?1.0 wt%⁵.0 wt%?,calcination temperature?450⁶50 ^oC?and reduction temperature?600⁸00 ^oC?on the morphology and catalytic performance of the prepared catalysts were investigated.The results indicate that the optimal calcination temperature and reduction temperature are 550 ^oC and 650 ^oC,respectively,and the optimal loading contents of Fe and Pd are 9.0 wt%and 1.0 wt%respectively in monometallic Fe/HZSM-5 and Pd/HZSM-5 catalysts.In the bimetallic Fe-Pd/HZSM-5 catalyst,Fe mainly exists in the form of oxidative state,and Pd mainly exists in the form of pure metal.The presence of FeO_x is beneficial to the dispersion of Pd nanoparticles,and the presence of Pd facilitates the reduction of FeO_x.The synergistic effect of FeO_x and Pd can effectively both improve the catalytic activity to depolymerize lignin and reduce the dosage of noble metal Pd.In addition,the existence of FeO_x inhibits the over hydrogenation of aromatic monomers,which is beneficial to the retention of aromatic ring;on the other hand,it promotes the weakening of aryl C-O bond,which is beneficial to break the unit bond of lignin.On this basis,Fe-Pd/HZSM-5 catalyst prepared under optimal conditions was used as the catalyst to investigate the effects of temperature,catalyst dosage,reaction time and hydrogen pressure on hydrogenolysis of sugarcane bagasse lignin to prepare aromatic monomers.GC-MS,GPC and ¹H-NMR were used to analyze the composition,structure and distribution of degradation products.The results indicates that the optimal reaction temperature,catalyst dosage,reaction time and pressure are 320 ^oC,0.08 g_cat/0.1 g_ligin,120 min and 1.0 MPa,respectively.In this condition,the yields of aromatic monomers and bio-oil are 27.92%and78.50%,respectively,and the degradation rate of lignin reaches 98.17%.