Study On Synthesis Of Ti-W-Ni Catalyst Based On MIL-125(Ti)and Their Catalytic Abilities For The Conversion Of Cellulose To Higher Alcohols

With the rapid development of human society,the shortage of fossil fuels and the problem of environmental pollution have become increasingly serious.From the perspective of sustainable development,more and more attention has been paid to the research on green and clean renewable resources.The conversion of lignocellulose biomass into sustainable chemicals and fuels is of great significance to reduce the dependence on fossil fuels.As the most abundant biomass resource,cellulose can be converted to higher alcohols（ethylene glycol,1,2-propanediol and etc）over catalyst,which is an efficient way to utilize biomass resources and has broad application prospects.The tungsten-based catalyst has excellent catalytic activity for the retro-aldol condensation reaction in the process of catalytic conversion of cellulose to lower alcohols,while Ni is proved to possess great catalytic ability in hydrogenation.In this paper,Ni and W components were supported on MIL-125（Ti）by impregnation method and then the composite was calcined in argon atmosphere.Finally,the Ti-W-Ni catalyst based on MIL-125（Ti）was prepared by hydrogen reduction.The catalytic activity of as-prepared samples was then evaluated in the hydrogenolysis process of cellulose to prepare higher alcohols.The single-factor control method was adopted to investigate the influences of active component loading,catalyst preparation conditions,and experimental conditions on the catalytic activity of Ni-W/M catalyst for the preparation of higher alcohols from cellulose.The results show that the highest yield of higher alcohols can be obtained using the catalyst with Ni and W loading amounts of20 wt%,which was prepared under the conditions of calcination temperature of 500 ^oC and calcination time of 4 h.The overall yield of higher alcohols achieved 83.9%and the conversion of cellulose was 100%over the catalyst under the optimized reaction conditions（initial H₂pressure of 4 MPa,reaction time of 2 h and reaction temperature of 245 ^oC）.Among them,the yield of ethylene glycol was 68.7%,and the yield of propanediol was 6.5%.The chemical structure,micro-morphology,elemental valence states,chemical bonds and acid sites of the catalyst were studied by means of BET,XRD,SEM,TEM,XPS,Raman and NH₃-TPD,which can well analyze the structural advantages of Ni-W/M catalyst.The results show that the Ni-W/M catalyst can maintain the original MOF framework without collapse and form Ti-O-W bonds on the catalyst surface,possessing the advantages of large specific surface area（102.77 m²/g）,appropriate average pore diameter（6.35 nm）,uniform dispersion of various active components,and abundant acid sites.The results of stability test of Ni-W/M catalyst show that the active component tungsten on the Ni-W/M catalyst is connected with Ti O₂ support through the Ti-O-W bonds,which reduces the loss of the active component tungsten in the reaction process,thus effectively maintaining the catalytic activity.The structure of Ni-W/M catalyst shows no obvious change after reaction,indicating that it has a stable structure.In the circulation experiment,the cellulose conversion rate and the yield of ethylene glycol did not decrease significantly,which demonstrated that the cellulose conversion rate remained at 100%and the target product ethylene glycol yield was still higher than 67.1%.Based on the analysis of the results,the main reaction routes for the preparation of higher alcohols from cellulose catalyzed by Ni-W/M catalyst was proposed.Firstly,cellulose was hydrolyzed to glucose under the combined effect of strong acidic site of Ni-W/M catalyst and H⁺produced by high-temperature water;then glucose was converted to glycolaldehyde through retro-aldol condensation under the effect of active component W;finally,the hydrogenation reaction was carried out under the catalysis of Ni to produce glycol and other higher alcohols.This work provides a new idea for catalyst design and preparation,through which people can well improve the catalytic performance and stability of the designed catalysts.