Direct Synthesis Of Hexitols From Microcrystalline Cellulose And Birch Over Ni/ZrP_x And The Mechanism Study

Under the background of "carbon peaking" and "carbon neutrality",it is more and more urgent to develop efficient "carbon neutralization technology".Biomass is the only renewable and abundant sustainable organic carbon source in the world.Among them,lignocellulosic biomass is a renewable biological resource with the widest distribution,the most variety,the widest source,and the lowest cost in the world.Therefore,the development and utilization of lignocellulosic biomass resources is an important part of the road to "carbon neutrality".Lignocellulosic biomass is mainly composed of cellulose,hemicellulose and lignin,in which the elements of C,H,and O account for more than 99%of the total element content,and the fine or bulk chemicals required for economic and social development are mainly composed of C,H,and O.Therefore,using lignocellulose resources to partially replace fossil resources to produce high value-added chemicals has good atomic economy and large-scale application prospects.Sorbitol,as one of the twelve most potential platform molecules derived from biomass,is widely used in drug synthesis,food processing,cosmetics preparation and other fields.As the main component of lignocellulose,direct and selective conversion of renewable cellulose to sorbitol is of great significance.However,due to the strong structure of cellulose,it is difficult to convert and utilize cellulose,which usually needs to be completed under harsh conditions of high temperature and high pressure.There are few studies to obtain single products including sorbitol with high selectivity from cellulose,mainly because the macromolecules obtained from cellulose hydrolysis are not easy to contact the active site on the catalyst surface,and the cellulose conversion is more complicated.Using cellulose as a substrate to produce sorbitol,most of the reported catalysts used Pt,Ru,Ir,Rh,Pd and other precious metals,or used ball-milling to pretreat cellulose to reduce the difficulty of cellulose conversion.This reduces the economics of cellulose conversion.Ni was the most widely used non-noble metal catalyst in the conversion of cellulose to sorbitol,but the yield of sorbitol obtained in most systems was low.Based on the present situation,it is necessary to design a strategy that convert cellulose or raw biomass into sorbitol in one pot with high selectivity under mild conditions.Herein,a series of phosphate solid acids were prepared and loaded with Ni(Ni/ZrPx)for cellulose conversion to produce high value-added sorbitol.Zirconium phosphate(ZrP2)exhibited the best catalytic activity among the screened catalysts.To explore the structure-function relationship for sorbitol production,systematic characterization studies including XRD,TEM,AAS,HADDF-STEM-EDS,XPS,FT-IR,NH3-TPD,and H2-TPD and comparative experiments were carried out.It was found that the precise regulation of the acid site and the hydrogenation site of the catalyst was crucial to inhibit humin formation and improve the yield of sorbitol.Using Ni/ZrP2 as the catalyst,60.8%yield of sorbitol was achieved when microcrystalline cellulose(1 wt%concentration)was used as the substrate.When the substrate concentration was increased to 5 wt%,50.8%yield of sorbitol was still produced.In addition,we also tested the direct depolymerization performance of the catalyst for raw biomass.40.2%yield of sorbitol and 67.9%yield of xylitol were obtained directly from birch wood.Through the systematic study and discussion of this work,the mechanism and regulation of cellulose transformation as well as the main influencing factors will have a clearer understanding,which has potential to promote the diversification of cellulose and even raw biomass conversion in the future.