Design And Synthesis Of Cobalt-Based Catalysts And Their Application In Catalytic Conversion Of β-O-4 Ketone Compounds

The lignin structure contains a large number of aromatic units,making it a candidate feedstock for the production of aromatic chemicals.At the same time,the structure also contains lots ofβ-O-4 bonds.Depolymerization of lignin into platform chemicals by crackingβ-O-4 ether bonds efficiently and then further upgrading to various carbon-based chemicals can reduce the dependence on fossil resources,which is of great significance to realize the“carbon peaking and carbon neutrality”goals.Therefore,efficient conversion of lignin into value-added chemicals,especially aromatic chemicals,with high selectivity is of great importance.Among the current transformation methods,hydrogenolysis ofβ-O-4 ether bond is a technical route with important application prospects.Cobalt-based catalysts are important non-precious metal materials,which have attracted much attention in hydrogenolysis reactions due to their low cost and high selectivity.In this paper,two efficient cobalt-nitrogen-doped carbon（NC）composite catalysts were prepared,and the effects of preparation conditions,metal center and pore size of the catalysts on the reaction were systematically studied.The main research contents and innovations of this paper are as follows:（1）Preparation of Co/NC catalysts and their performance for hydrogenolysis ofβ-O-4 ketonesVarious porous NC supported metal nanoparticle catalysts were prepared by hard template method,and their performances were tested for hydrogenolysis ofβ-O-4 ketone lignin model compounds.The results showed that the cobalt-based catalyst（Co/NC-900）obtained by calcining at 900℃in nitrogen atmosphere had the best performance,which could catalyze 2-phenoxyacetophenone to ethylbenzene and phenol effectively,with the yield of 99.0%.Further studies showed that the catalytic system could efficiently convert variousβ-O-4 ketones with methoxy groups and obtained the desired products in high yields.The excellent catalytic performance was related to suitable cobalt nanoparticle size,larger pores and large specific surface area.We proposed corresponding reaction pathways on the basis of control experiments.In addition,the catalyst was quite stable during the reaction,and there was no considerable loss of activity after being reused for five times.（2）Preparation of Co@NC catalysts and their catalytic reductive amination ofβ-O-4 ketonesUsing colloidal SiO₂ as a sacrificial support,NC supported cobalt nanoparticle catalysts（Co@NC）were successfully prepared and used for the reductive amination ofβ-O-4 ketones to primary amines.Research showed that calcination temperature and different ligands had significant effects on the performance of catalysts.The catalyst obtained by calcining at 900°C could achieve efficient reductive amination ofβ-O-4 ketones at a lower temperature（140°C）and a shorter time（6 h）（the yield of primary amine was 90%）.Detailed study indicated that the excellent performance of the catalyst was attributed to the coating of carbon,the uniform distribution of cobalt nanoparticles and the Co-N_x structure.The catalytic system could convert different kinds ofβ-O-4 ketones with methoxy groups to obtain target products efficiently.After repeated use for five times,the product yield did not decrease obviously.Based on the results of control experiments,a possible reaction pathway for the reductive amination process was proposed.