Studies On Chemical Synthesis Of Ethanol From Cellulose Catalysed By Zirconium Oxide Supported Platinum Catalyst And Tungstic Acid

The catalytic transformation of biomass,the only renewable organic carbon resource in nature,into value-added oxygenates such as ethanol is a promising route for biomass utilization.Since biomass,in particular lignocellulosic biomass,contains abundant oxygen,the transformation of it into oxygen-containing chemicals agrees well with the atomic economic.As a key chemical,ethanol is mainly produced by fermentation of carbohydrates such as glucose.However,these biological methods employ edible biomass as the feedstock.Moreover,the enzyme is expensive and requires to be operated under strict reaction conditions.Thus,the development of a new route for the production of ethanol is of great importance and highly desirable.In this context,we developed a chemical catalytic approach for the direct transformation of cellulose,the most abundant in-edible biomass,to ethanol and obtained the following results:By combining tungstic acid and a supported metal catalyst,we performed the conversion of cellulose into ethanol under hydrothermal conditions in hydrogen.The catalytic performances of Pt nanoparticles loading on various metal oxides(e.g.ZrO2,SiO2,TiO2,Al2O3,MgO,CeO2 etc.)and ZrO2 supported different metals(e.g.Pt,Pd,Ru etc.)were carefully compared,and among these catalysts Pt/ZrO2 exhibited the highest yield to ethanol.Under the reaction conditions of 250 ?,P(H2)=4 MPa,5 h,tungstic acid and Pt/ZrO2 could afford more than 30%of ethanol from cellulose reaction.Mechanic studies suggest that tungstic acid and Pt/ZrO2 played different roles in the reaction.Under the hydrothermal conditions,the in-situ formed reversible protons and tungstic acid could catalyze the hydrolysis of cellulose to glucose,which was then activated by tungstic acid and converted to glycoaldehyde via retro-aldol fragmentation for cleaving C2-C3 bond.Next,Pt/ZrO2 catalyzed the hydrogenation of glycoaldehyde to ethylene glycol in the presence of H2.The further hydrogenolysis of ethylene glycol gave rise to ethanol.Beside this pathway,the formed glucose could undergo isomerization and form fructose,which was subsequently converted to C3 intermediates such as dihydroxylacetone through retro-aldol fragmentation.The hydrogenation of hydrogenolysis of C3 compounds finally yielded propanol,dihydroxyl propanol,and even ethanol.The correlation of the performances and characterizations of the catalysts indicates that the unique ability of Pt/ZrO2 for hydrogenation is the key for the formation of ethanol in the cellulose reaction.The specific surface areas and the acidity only exerted limited effect on the performances of the catalysts.