Hydroconversion Of Cellulose To Hexitols Over Pt/γ-Al₂O₃

Cellulose is the most abundant biomass in nature, and catalytic conversion ofcellulose efficiently to fuels and fine chemicals has the vital significance to ease theenergy crisis. γ-Al2O3as an important catalyst support has a wide range ofapplications. We have synthesized γ-Al2O3with different pore structure andPt/γ-Al2O3catalyst. The influence of pore structure, property of surface and Pt particlesize on cellulose hydrogenation were investigated.Firstly, ordered mesoporous γ-Al2O3(MA) was synthesized via one-potevaporation-induced self-assembly method using pluronic P123block copolymer as asoft template and aluminum iso-propoxide as metal precursor. X-ray diffraction(XRD), N2adsorption-desorption (BET), transmission electron microscopy (TEM)and thermal analysis techniques (TGA) were used to characterize their properties. Theresults reveal that alumina possess a highly ordered2D hexagonal mesostructure,which is resistant to high temperature up to800°C. And the crystalline structure ofAl2O3was converted to γ-Al2O3phase after further treatment at800°C. After calcinedat1000°C, the mesoporous structure has collapsed and diffraction peaks of-Al2O3phase appear in the wide-angle XRD pattern. With Pt/MA as catalyst, we investigatedfactors including calcination temperature, reaction temperature, reaction time andamount of catalyst. The reusability and deactivation of catalyst was also investigated.According to the analysis of reaction results, the catalyst, with the catalyst supportprepared at800°C and the catalyst prepared at temperatures ranging from400to600°C, revealed a good performance. The optical reaction conditions for the celluloseconversion was operated at200°C for4h, resulting a better hexitols selectivity whichin the case of the yield of hexitols reached to27.59%with35.14%celluloseconversion.Hierarchically mesoporous-macroporous Al2O3(HMMA) was prepared byself-formation phenomenon with aluminum sec-butoxide as metal precursor.Pt/γ-Al2O3catalysts were prepared by impregnation method. SEM results revealedgood thermal stability of the hierarchically mesoporous-macroporous structure ofalumina. TGA, TEM and NH3-TPD results showed that hydroxyl density and totalacid sites of Al2O3reduced with the increasing calcination temperature, while Pt particle size increased with the increasing calcination temperature. With Pt/HMMA ascatalyst, we also investigated factors including calcination temperature, reactiontemperature, reaction time and amount of catalyst and so on. The optimal conditionwas that0.16g cellulose,0.068g Pt/HMMA-400catalyst,24h and190°C. Thecellulose conversion was54.95%and the yield of hexitols reached to38.99%. Theresults of catalysts reusability showed that γ-Al2O3was unstable and converted into ahydrated boehmite (AlOOH) phase in hot liquid water. We could reduce thedeactivation of catalyst by shortening the reaction time.