Hydrochar Functionalized Loaded Aluminum And Its Mechanism In Glucose To Fructose Isomerization

The suite for alternative approaches to chemical production using non-petrochemical and renewable resources has been increasing because of the continuing energy crisis,environmental pollution,and global warming over the years.And in the cascade reactions of biorefinery,the challenge to isomerize glucose to fructose（Glu-Fru）limits the conversion efficiency of glucose to value-added chemicals.A great deal of effort has tried to develop various catalysts for the efficient isomerization of Glu-Fru.In this study,hydrochar loaded Al-oxide nanoparticles catalysts were prepared for efficient Glu-Fru isomerization.1)Effect of swelling pretreatment on properties of cellulose based hydrochar.In this study,both trifluoroacetic acid（TFA）and phosphorous acid（PA）under low temperature were used as swelling solvents to disrupt the cellulose（CEL）crystalline structure within 1 h with distinct physicochemical properties.The results showed that the TFA and PA swelling pretreatment significantly enhanced the dehydration and deoxidation of cellulose through HTC process.The H/C value and O/C value of swelled cellulose are lower than non-swelled by more than 4%at 220°C,demonstrating that the dehydrogenation reaction is enhanced during the hydrothermal process of swollen cellulose.Particle size as well as microscopic arrangement of hydrochars were distinctly different due to swelling cellulose.The particle size of hydrothermal carbon microspheres increases by the swelling process at the same hydrothermal carbonization temperature.TFA-HC have an estimated diameter of 0.2μm at 220°C,which is equivalent to the size of CEL-HC-280.This study illustrates the mechanism for hydrothermal carbonization of TFA and PA swollen cellulose,and provides a novel route for the directionally regulating hydrothermal carbon microspheres and developing carbon-based catalyst support.2)Glucose isomerization catalyzed by swollen cellulose derived aluminum-hydrochar.Since efficient isomerization of Glu-Fru is vital for valorizing cellulose fraction of biomass to value-added chemicals,an approach of engineering aluminum-hydrochar catalyst by impregnating aluminum on swollen cellulose derived hydrochar has been studied.The results showed that Al-hydrochar calcinated at 300℃achieved fructose yield of 26.3%in acetone/H₂O reaction medium.It was found that the amorphous Al structures with nano-size on the surface of the carbon microspheres were the major contributor of the catalytic activity on Glu-Fru isomerization,while the formation of Al crystal had an inhibition effect on glucose isomerization.The deactivation study of Al-hydrochar catalysts showed the exfoliation of colloidal carbon containing aluminum active catalytic sites.3)Insights into the glucose isomerization mechanism of Al-hydrochar catalyst probed by Al-oxide species transformation.This study proposed one-pot hydrothermal carbonization as an eco-friendly and facile approach to engineer aluminum（Al）-hydrochar catalyst for effective Glu-Fru isomerization.Different hydrothermal temperatures for in-situ loading Al-oxide species on hydrochar support and the catalytic active sites modification via calcination in oxygen were investigated.The transformations mechanism of Al-oxide species at varying hydrothermal and calcination temperatures was explored.The results showed that nano-size Al-containing species were uniformly loaded on carbon support via hydrothermal carbonization below 200℃and the prepared Al loaded hydrochar at 180℃after calcination at 300℃yielded 39.5%fructose with92.6%selectivity in acetone/water reaction medium at 160℃for 20 min.The catalysts prepared at a hydrothermal temperature below 200℃facilitated the formation of an amorphous Al-containing structure less than 0.5 nm,and calcination at 300℃under aerobic conditions formed the effective active sites.4)Facile one-pot synthesis of aluminum nanoparticles loaded on hydrochar spheres for glucose to fructose isomerization.Corn stover derived hydrochar doped with aluminum nanoparticles was synthesized through the facile one-pot hydrothermal carbonization for Glu-Fru isomerization.Amorphous aluminum nanoparticles with crystalline size less than 0.5 nm were uniformly loaded on hydrochar.The phase of the Al nanoparticles was tailored through aerobic/anaerobic calcination.The results showed that the amorphous aluminum nanocrystals with six coordinated Al structure were formed under oxygen calcination,which facilitated the high catalytic activity and selectivity of glucose isomerization.It was found that catalysts prepared at hydrothermal temperature of 180℃and further calcinated at 300℃under aerobic condition(Al/HC₁₈₀-300/O)achieved a fructose yield of 42.6%and a selectivity of 83.6%at 180°C for 5 min.The kinetics,catalytic mechanism,and the deactivation mechanism of the Glu-Fru were further studied.This study provides an efficienct and low metal loading carbon-based catalysts synthetic approach for biorefinery.