A Study Of Selective Hydrogenolysis C-O Bond Of Biomass Polyols Over Ru-MoO_x/Mo₂C Catalysts

1-hexanol,a linear higher alcohol with a six-carbon chain,is recognized as an important chemical feedstock or intermediate with wide applications in the perfume,medicine,food,textile and polymer industries.The commercial production of 1-hexanol still relies on petroleum-based production routes,including the Ziegler alcohol synthesis and the hydroformylation of n-pentene followed by hydrogenation.Such kind of industrial synthesis faces many problems such as multi-step syntheses,complex separation processes and harsh reaction conditions,making the current approaches neither sustainable nor environmentally friendly.In addition,the conventional Fischer-Tropsch（FT）synthesis has been identified as a potential route for higher alcohol synthesis from syngas directly.However,due to the lack of an effective catalyst with high stability,the low selectivity of 1-hexanol in the products severely limits its large-scale application.Recently,the use of biological fermentation technology to convert glucose into 1-hexanol has attracted people’s attention.However,this technology cannot meet the requirements of industrial production and commercial operation due to the low enzymatic activities,the less toxicity tolerance of microbes,and the low selectivity of 1-hexanol.Therefore,it is necessary to explore a process for efficiently synthesizing 1-hexanol from biomass raw materials.The purpose of this study is to explore the process of selective hydrogenolysis of the C-O bond of sugar alcohols derived from biomass resources into corresponding higher alcohols,Using sorbitol as a model reactant,the hydrodeoxygenation performance of the molybdenum-based catalysts were investigated.Theβ-Mo₂C,Mo₂N,Mo P,molybdenum carbide passivated samples and molybdenum carbide supported metal samples were prepared by TPR（temperature programmed method）.The physical and chemical properties of the catalysts were analyzed by XRD,XPS,HR-TEM,NH₃-TPR,H₂-TPR,DRIFTS and other characterization methods.At the same time,the catalytic activity,process conditions,catalytic stability and sorbitol conversion path of the 2Ru-2MoO_x/Mo₂C catalyst in the selective hydrogenolysis of sugar polyols C-O bond were systematically studied.1.Screening of the molybdenum-based catalysts suitable for selective hydrogenolysis of C-O bond of sorbitol to produce 1-hexanol,and the catalytic activity of six catalysts（2Ru/MoO_x,2Ru/Mo₂N,2Ru/Mo S₂,2Ru/Mo P,2Ru/Mo C,2Ru/Mo₂C）were investigated.The products contained 58.5%1-hexane when Mo₂C was used as the catalyst for deoxygenation and hydrogenation of sorbitol,indicating that Mo₂C could fully break the C-O bond while retaining the original carbon chain.In addition,the performance of the hydrogenolysis activity of different modified molybdenum carbide catalysts indicated that the MoO_x layer on the surface of the catalyst could suppress excessive hydrodeoxygenation of sorbitol,and retaine the terminal hydroxyl groups of sorbitol.2.The effects of reaction parameters were investigated on the catalytic performances,including the loading amount of Ru and MoO_x on the surface of molybdenum carbide,reaction temperature and pressure,concentration of sorbitol,gaseous hourly space velocity（GHSV）and liquid hourly space velocity（LHSV）,and stability of the catalysts.With 2Ru-2MoO_x/Mo₂C as the catalyst,the yield of 1-hexanol reached 28.7%under the optimized conditions of 523 K,6 MPa H₂,20 wt%sorbitol solution,GHSV=514.3 h^-1,and LHSV=0.343h^-1.The characterization results of the catalysts showed that after the introduction of Ru and MoO_x into molybdenum carbide,the content of Mo²⁺and Mo⁴⁺on the surface of the catalyst decreased remarkably,and Mo⁶⁺corresponding to MoO₃became the major species.At the same time,the number of strong acid sites was noticeably shrunk to slightly more than half,while the number of weak acid sites increased significantly.In addition,the adsorption/desorption capacity of C-O on the surface of the catalyst have been weakened.These might explain why 1-hexanol was not further deoxygenated and hydrogenated to 1-hexane.3.The research results of hydrogenolysis of various sugar alcohols on 2Ru-2MoO_x/Mo₂C showed that those polyols such as xylitol,erythritol,glycerol and ethylene glycol could selectively break the C-O bond to generate the corresponding 1-pentanol,1-butanol,1-propanol,ethanol,etc.The reaction path of sorbitol hydrodeoxygenation to 1-hexanol was discussed.Firstly,sorbitol was dehydrated to form isosorbide,then isosorbide underwent a series of deoxygenation and hydrogenation reactions to form polyols,finally the polyols were further hydrodeoxygenated to form 1-hexanol.