The conversion of glucose and selectivity into 5‐hydromethylfurfural (HMF) were investigated over various silica–alumina composite (AlSiO) catalysts. The type, amount, and strength of the acidic sites were characterized by using NH3 temperature‐programmed desorption and FTIR spectroscopy and then correlated to the catalytic conversion of glucose into HMF to provide a quantitative relationship between the acidity and product selectivity. Lewis acid sites played an important role in glucose conversion, which can enhance the isomerization of glucose to fructose, whereas Brønsted acid sites had a detrimental effect. HMF selectivity had an almost linear relationship with the weak/total Lewis acid ratio (L*/L), indicating that weak Lewis acids could promote formation of HMF. The medium‐to‐strong Lewis acid sites can enhance the formation of undesired byproducts (levulinic acid, humins). The Brønsted to Lewis acid ratio (B/L) had an influence on the HMF selectivity; at similar L*/L ratios, volcano curves were obtained with the increase of the B/L ratio, but the influence was not as great as that of the L*/L ratio. Nb‐doped AlSiO catalysts were prepared and used in the conversion of glucose into HMF, which also confirmed the above findings. Under the optimized conditions, the HMF selectivity can reach 71 % at 92.6 % conversion of glucose with no clear decline after four catalytic cycles.

The conversion of cellulose from renewable biomass into the key platform chemical, 5hydroxymethylfurfural (HMF), is of fundamental importance to the production of numerous bioproducts and biofuels. Various acidic catalysts have been developed for this process; however, most systems suffer from low efficiency and poor sustainability. Here we report an acid-free conversion of cellulose into HMF in a biphasic system of tetrahydrofuran/concentrated seawater. The yield of HMF reached 48.6%, and this system has excellent reusability and sustainability. We found that the chloridions (Cl -) can promote the isomerization of glucose via a 1,2-hydride shift path and accelerate the dehydration of fructose, thus driving the selective formation of HMF. This simple system is capable of converting raw biomass to furfural and HMF with the lignin residues transformed into useful alkanes via a sequential catalytic upgrading, paving a new economic-viable pathway for the full valorization of lignocellulosic biomass. catalysts with great abundance, easy recovery and, most importantly, reduced acidity to enhance the efficiency, reusability and sustainability, is the key to improve the HMF production. Scheme 1. The reaction pathway for the conversion of cellulose to HMF and the potential application of HMF as a platform chemical.Seawater is the most abundant natural resource in the world and there is an increasing need to improve its utilization. For example, seawater can be readily concentrated by sunlight to extract salts.Herein, we describe the conversion of cellulose to HMF with a high yield of 48.6% catalyzed by concentrated seawater (ca. 30 wt% salts) in a THF/seawater biphasic system in the absence of any external-added acid catalysts. An investigation combining control experiments, DFT calculations and D2-glucose isotopic labeling reveal that the halogen ions, chloridions in this case, play a key role in the cellulose hydrolysis, glucose isomerization and fructose dehydration, resulting in the selective HMF formation. This new process is overall extremely simple, inexpensive, and efficient for the mass production of HMF from renewable woody biomass. Importantly, transformative insight is uncovered to remove the current reliance on the use of dual acids (i.e., Lewis and Brønsted acid) for the conversion of cellulose to HMF.

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Mesoporous AlSiO catalysts have been prepared by a facile sol–gel method with tunable acidity for highly efficient production of HMF.

The direct transformation of lignocellulosic biomass into valuable chemicals and fuels, which is recognized as a promising strategy for easing the present situation of energy depletion, has brought a hot-spot of research. Here we describe the one-pot catalytic conversion of cornstalk into liquid alkylcyclohexanes (from lignin fraction) and polyols (from cellulose and hemicellulose components) over Ru/C catalysts, which are prepared by oxidized commercial Ru/C and then reduced at different temperature. These Ru/C catalysts are well-characterized by the techniques of X-ray photoelectron spectroscopy, H2-TPR, and NH3-TPD correlated with the conversion of cornstalk and products distribution. It is found that the Ru/C catalyst reduced at 300 °C has the best performance for cornstalk conversion; the mole yield of liquid alkylcyclohexanes reached 97.2% (based on lignin monomers in cornstalk) with 52.7% polyols (24.5% sorbitol, 12.2% xylitol, and 16.0% C2–C4 polyols) at 200 °C. The detailed investigations reveal a synergistic effect between Ru and RuO2 species in the conversion of lignocellulosic biomass, where metallic Ru is responsible for hydrogenation and RuO2 species plays crucial roles in cleaving the interlinkages of lignin–carbohydrate (ester and ether linkages) efficiently and in promoting the retro-aldol condensation of carbohydrates. Furthermore, the Ru/C-300 catalyst can be reused for five runs and can be extended to several different raw biomass substrates, indicating that this Ru/C catalysts-based reaction system is promising for the total conversion of lignocellulosic biomass into liquid alkylcyclohexanes and polyols.