| 其他摘要 | Conversion of biomass feedstocks towards value-added chemicals is an important route to establish the sustainable industry and economy. Lignocellulose, the most abundant non-food biomass, could be easily degraded to sugars. Herein, a highly efficient catalytic conversion of biomass-derived sorbitol which could be largely obtained from the hydrogenation of glucose, the largest biomass-derived sugars, into glycerol and glycols was studied in detail.A highly active metal-base bifunctional catalyst system for the hydrogenolysis of sorbitol towards glycerol and glycols was designed and investigated to solve the thorny issues as reported previously, like the liquid alkalis added and the harsh conditions needed. MgO, carbon nitride (CN) and hydrotalcite (HT) supported Ni, Cu and Co catalysts were prepared by impregnation and coprecipitation, respectively, and employed in sorbitol hydrogenolysis without the addition of basic promoters. From the detailed studies in the influences of solid base carriers, preparation methods, active metal species, metal content, calcination temperature and reduction temperature on the catalytic performance, the best catalyst of Ni-MgO prepared by coprecipitation with 35% Ni content, calcined and reduced at 500 °C was obtained. The reaction parameters were optimized as 200 °C, 4 MPa initial H2 pressure and 4 h reaction time, under which a 67.8% conversion with a 86.5% total selectivity of glycerol, 1,2-propylene glycol and ethylene glycol was obtained. The higher temperature enhanced sorbitol consumption and product degration, whereas sorbitol conversion and glycerol yield were increased and the deep degradation of glycols was accelerated with the increasing H2 pressure or the prolonged reaction time.The bifunctional effect of metal-base catalysts on sorbitol hydrogenolysis was also investigated with the employment of Ni-MgO catalyst chosed. The results of sorbitol hydrogenolysis over Ni catalysts loaded on a series of carriers with varying basicities and in the Ni-MgO catalyst system with modulated basicity by NaOH added or Al2O3 dopped showed that, the stronger and appropriate basicity in catalysts favored the higher activity and the alkaline additive was not necessary but harmful for Ni-MgO catalyst. Raney Ni catalyst with MgO added exhibited poorer performance than Ni-MgO catalyst, and the degradation of catalytic activity was observed in the Ni-MgO catalyst recycling texts owing to the aggregation of Ni particles as MgO was partly eroded, indicating that the well-dispersed Ni particles was also essential. The results of hydrogenolysis experiments and catalyst characterization suggested that, the synergistic effect between active Ni metal sites and basic sites should exist when Ni nanoparticles were in close proximity with the size-comparable MgO particles. Hence, the retro-aldol condensation with C-C scission and the hydrogenolysis reaction should be catalyzed together by Ni metal sites and basic sites in Ni-MgO catalyst, which showed the bifunctional catalytic effect on sorbitol hydrogenolysis. The promoted effect of catalytic additives of NaOH and non-alkaline metal oxides like WO3 and MoO3 on Ru/C catalysts for sorbitol hydrogenolysis were also studied, respectively. These preliminary studies revealed that WO3 played the biggest but still limited role in the promotion. |
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