Preparation Of Hydrochar Based Catalyst Derived From Water Hyacinth And Its Mechanism For Glucose Isomerization

The abundant aquatic biomass shows great potential for valorization in China.However,current treatments on aquatic plants were inefficient and of low economic value.In addition,the catalysts for biorefinery which converts waste biomass into a variety of high value-added liquid fuels and chemicals,were complex,low efficiency,and high cost.Therefore,exploring new processes to realize the high-value-added utilization of aquatic plants and the efficient isomerization of glucose,which is the crucial step of the biorefinery,is of great significance to our country’s environment and energy structure.This study prepared functional hydrochar derived from the aquatic plant via hydrothermal carbonization.By urea modification and calcination activation,hydrochar-based catalysts with high catalytic activity for glucose isomerization were synthesized.The influence of hydrothermal carbonization,urea modification,and calcination activation on the physical and chemical properties of hydrochar and hydrochar-based catalysts was clarified.Based on machine learning and interpretable methods,the key factors and interaction mechanisms to regulate the efficiency of glucose isomerization catalyzed by hydrochar-based catalysts were analyzed.This study provided a new idea and theoretical basis for the valorization of aquatic biomass and the efficient isomerization of glucose.(1)Preparation of hydrochar derived from aquatic plant and urea modification mechanism.Water hyacinth was transformed to hydrochar via hydrothermal carbonization and was modified by introducing urea.The mechanisms of hydrothermal temperature and urea concentration regulating the physicochemical properties of hydrochar were studied.The results showed that 240℃ was suitable to produce uniform hydrochar rich in pore structures(especially macropores and mesopores).Adding 0.5 mol/L urea during the hydrothermal carbonization was conducive to promoting the nucleation and growth of carbon microspheres which were uniform and in strong monodispersity.Besides,the ammonia and carbon dioxide generated by the decomposition of urea at high temperatures could increase the pores(especially the macropores and mesopores)of hydrochar with the space occupation effect.In terms of chemical properties,introduced urea could increase the active sites on the outer and inner surfaces of hydrochar by promoting the crystallization of endogenous alkaline calcium in water hyacinth and forming highly active nitrogen-containing functional groups(such as amide,quaternary ammonium,etc.).This study proposed a low-cost,environmental-friendly and universal process for the efficient conversion of aquatic plants into high-value functional carbon material.(2)Preparation of hydrochar-based catalyst and its catalytic performance.Hydrochars modified by urea were transformed into hydrochar-based catalysts,which exhibited special micromorphology and excellent physicochemical properties by calcination activation.The mechanisms of calcination temperature and oxygen content in the calcination environment regulating the physical and chemical properties of the hydrochar-based catalyst were analyzed.With glucose isomerization as the indicator reaction,the catalytic performance of the hydrocharbased catalyst was evaluated,and the catalytic site and mechanism were clarified.The results showed that calcination activation further increased the calcium crystals in hydrochar,increasing the number of active centers in the hydrochar-based catalyst.Additionally,it promoted the conversion of calcium oxalate with weak alkaline into calcium carbonate with moderate alkaline enhancing the alkalinity of hydrochar-based catalyst.Most importantly,surface oxygencontaining functional groups were also increased.Since these groups were closely connected with the active sites,the possibility of calcium leaching or catalyst deactivation was significantly reduced.In terms of physical properties,calcination activation could increase the pore number with the uniform micromorphology of hydrochar kept,especially when calcined under ample air.Plenteous large pores and mesopores ensured the accessibility of calcium salt(active site)for reactant.Besides,unique etching on calcium salt caused by calcination activation made the solid active sites hollow out at multiple levels,further increasing the accessibility.The catalyst with the best performance could achieve 31% fructose yield with 89% selectivity within 45 min in water at 120℃,equivalent to the catalysts doped with precious metals.The catalytic activity could maintain at least maintained at least three times.This study provided a new,economic,and highefficiency catalyst for the isomerization of glucose to fructose.(3)Interpretable machine learning-based analysis of mechanism in glucose isomerization catalyzed by hydrochar-based catalysts.Literature on the glucose isomerization catalyzed by hydrochar-based catalysts in the recent five years was compiled,and data sets containing 120 groups of acidic Al-doped catalysts and 52 groups of basic Ca-induced catalysts were formed.Integrated XGBoost was applied to systematically map catalytic results as a function of the preparation parameters and physicochemical properties of catalysts as well as the catalytic conditions.The machine learning model was deeply explained with the key factors and interaction mechanisms of acidic and alkaline hydrochar-based catalysts for glucose isomerization clarified based on partial dependence analysis and SHAP analysis.The results showed that,for the acid Aldoped catalysts,the half peak width of oxygen must be greater than 2.83 e V so that the Al could be transformed into effective catalytic sites.That is to say,effective Al sites were coupled with hydrochar in specific forms.In addition,when Al/C<0.05,the catalytic activity can be improved by appropriately increasing the Al loading.For the alkali Ca-induced catalysts,the side reactions could be effectively reduced with the catalytic temperature lower than 130℃.Besides,the catalytic performance could be improved by increasing the large pores and mesopores and increasing the accessibility of active sites.This study not only proposed a novel idea for the regulation and optimization of hydrochar-based catalysts but also provided a good reference for machine learning applications in biorefinery.