Study On Selective Hydrolysis Of Sorbitol To Higher Alcohols Over Ru-Mo/CMK-3 Catalyst

Nowadays,higher alcohols(C₂₊alcohols)are more desirable products,as neat alcohol fuels,fuel additives,and fine chemicals,than methanol.The main technical routes for the production of C₂₊alcohols include catalytic synthesis via syngas and biological fermentation.However,these synthetic routes also face many great challenges.Despite the conversion ofsyngas to many different products,such as hydrocarbons and methanol,has been widely applied in the large-scale industrial production,the catalytic synthesis of C₂₊alcohols is severely limited on the small-scale studies due to lack of suitable catalysts.From acommercial point of view,the catalytic activity,selectivity and yield of C₂₊alcohols for current transition metal catalysts are fairly poor,and significant improvements should be achieved to make this synthetic route more attractive.Meanwhile,as a fuel additive,ethanol has spurred the people's particular interest because it can be produced by biological fermentation from renewable biomass-derived sugars.Nevertheless,the fermentation process requires to consume a large number of biomass feedstock,e.g.corn and sugar cane,so as to result in the problem of a rapid rise in the price of sugars and food during the extensive application of ethanol.Moreover,compared with the alcoholic fermentation,it is difficult to produce C₅₊alcohols with high yield by yeastmetabolism during the fermentation process,and the C₅₊alcohols selectivity is highly dependent of the genus,specie and strain of yeast and the specific nutrients?nitrogen and amino acids?.Low conversion rate of raw material and low concentration of C₅₊alcohols lead to high production cost,which cannot meet the requirements of industrial production and commercial operation.Actually,in the higher alcohols,C₅₊alcohols are even more remarkable due to its utilization as high value-added fine chemicals and its high heating values as diesel additives.Accordingly,how to furtherly improve the proportion of C₅₊alcohols in the total alcohol products is extremely challenge.The purpose of our present research is to explore such a process capable of converting sugar alcohols derived from biomass resources to higher alcohols by catalytic hydrogenolysis,and preferably with high selectivity to higher value C₅₊alcohols.Our previous works mainly focused that the transformation of sugar polyols to renewable C₅-C₆alkanes over Ru-Mo/C catalysts by the selective dissociation of C-O bonds and suppressing the excessive cleavage of C-C bonds.In contrast,in order to produce C₂₊alcohols,the C-O bonds in sorbitol should be selectively cleaved,while the excessive dissociation of C-O bonds to form alkanes should be efficiently prohibited.As a typical ordered mesoporous carbon material,the superior performance of CMK-3 has been widely known in aqueous catalysis as a water-tolerant support,owing to high surface areas,periodic mesopores,uniform pore size,adequate pore volume and high hydrothermal and chemical stabilities.Presently,we effectively designed the Ru Mo bi-functional catalysts supported on the mesoporous carbon CMK-3,and successfully applied them in the catalytic hydrogenolysis of sorbitol.It was found that the synergetic effect of Ru and Mo species,different Ru precursors and the mesoporous channel effect of CMK-3 were the key factors for direct hydrogenolysis of sorbitol to higher alcohols.At present,we have effectively designed a mesoporous carbon cmk-3 supported Ru Mo bifunctional catalyst and successfully applied it to the catalytic hydrolysis of sorbitol.Taking them as research objects,the effects of pore structure,chemical properties and catalytic performance of Ru-Mo/CMK-3 catalyst and its causes were explored by combining various methods of catalyst characterization?N₂physical adsorption,XRD,TEM,SEM,H₂-TPR,XPS,etc.?.At the same time,the effects of different reaction temperature and air speed on the performance of catalyst wereinvestigated.In the temperature range of 473 K-553 K,the yield of C₂₊alcohol increased significantly with increasing temperature.The low temperature leads to a low conversion rate of sorbitol,and also leads to the formation of intermediate oxygen compounds.High temperature is conducive to the cracking and hydrogenation activity of the C-O bond on the Ru-Mo?acac?/CMK-3 catalyst,so sorbitol is most likely to be converted to C₁-C₆ alkane.As the reaction temperature further increases,the content of C₂₊alcohol gradually decreases.The product distribution shifts to lower-carbon alkanes,thereby forming a deep hydrodeoxygenation,which may be due to the acceleration of the C-C bond breakage due to the excessively high temperature of Ru metal.Therefore,an appropriate reaction temperature can increase the reaction rate,promote the hydrogenolysis reaction,and maximize the C₂₊alcohol.It can be seen that proper temperature can promote incomplete dehydration and hydrogenation to form oxygenated compounds,resulting in a lower yield of gaseous products.Therefore,too high or too low temperature will reduce the catalytic performance of the catalyst.When the pressure increases,it has a positive effect on the production of C₂₊alcohol,but excessively high H₂ pressure will increase the concentration of H₂ in the metal active site,which is beneficial to the hydrogenation reaction,causing carbon to transfer from the aqueous phase to the gas phase,resulting in the production of C₂₊alcohol The rate fell sharply.In addition,the effect of reaction time was also investigated.As the reaction time increases,the yield of C₂₊alcohol gradually increases,but as the reaction time continues to increase,the yield of C₂₊alcohol is lower.Since the longer reaction time will lead to the hydrohydrolysis of sorbitol,the product distribution becomes gaseous alkanes.The support of CMK-3 carrier has a significant effect on the performance of sorbitol hydrogenolysis to C₂₊alcohol,which may be due to the ordered mesoporous pores and larger pore diameter of CMK-3,which is conducive to the adsorption/desorption of reactants and Diffusion of intermediate compounds in the sorbitol hydrodeoxygenation reaction.In addition,different Ru precursors have a significant effect on catalytic performance.In the presence of different Ru precursors,the Ru-Mo?acac?/CMK-3 catalyst can greatly inhibit the excessive cleavage of C-C bonds and C-O bonds,making the yield of gaseous alkanes very low.By introducing metal Mo into the ruthenium-based catalyst,the Ru-Mo?acac?/CMK-3catalyst can further suppress deep hydrodeoxygenation,and the yield of C₂₊alcohol is greatly increased.On the other hand,it shows lower production of C₁-C₆ alkanes,which is almost negligible.This shows that the synergy of Ru and Mo is very important.The introduction of a suitable metal Mo with partial reduction state?Mo O₃-x?can selectively cleave the C-O bond,effectively converting multiple biomass-derived oxygenates into C₂₊alcohols.In order to further understand the reaction mechanism and catalytic mechanism of the research on the aqueous catalyst for the preparation of higher alcohols from biomass sugar alcohols,the end of the thesis provides prospects and suggestions for future research work.