Jinxu Xi

Direct conversion of carbohydrates to 5-hydroxymethylfurfural using Sn-Mont catalyst

5-Hydroxymethylfurfural (HMF) is a very important intermediate in the fine chemical industry. This study aims to investigate the direct conversion of glucose or glucose-based carbohydrates, such as sucrose, cellobiose, inulin, starch and cellulose, to HMF by using a Sn-Mont catalyst. With the use of this catalyst, a HMF yield of 53.5% was achieved from glucose in a mono-phase medium of tetrahydrofuran (THF)/dimethylsulfoxide (DMSO) at 160 °C for 3 h. The success of one-step conversion of glucose to HMF is attributed to the Sn-Mont catalyst containing two types of acid sites, Lewis acid and Bronsted acid sites. The former one plays a crucial role in the isomerization of glucose to fructose and the latter one is active in the dehydration of generated fructose to HMF. Furthermore, Sn-Mont catalyst also demonstrated excellent activity in the conversion of disaccharides and polysaccharides and as high as 39.1% HMF was directly obtained from cellulose in a THF/H2O–NaCl bi-phasic system.

High-yield production of levulinic acid from cellulose and its upgrading to γ-valerolactone

Direct catalytic conversion of cellulose to levulinic acid (LA) by niobium-based solid acids and further upgrading to γ-valerolactone (GVL) on a Ru/C catalyst were realized through sequential reactions in a reactor. Firstly, using aluminium-modified mesoporous niobium phosphate as a catalyst, cellulose can be directly converted to LA with as high as 52.9% yield in aqueous solution, even in the presence of the Ru/C catalyst. To the best of our knowledge, this is the best result over a heterogeneous catalyst so far. It was found that the type of acid (Lewis and Bronsted acids) and acid strength had an influence on the yield of LA; the doping of aluminium can enhance the strong Lewis and Bronsted acids, especially the strong Lewis acid, thus resulting in the increase of LA yield from cellulose as well as from glucose and HMF. Such an enhancement by a Lewis acid on LA yield from HMF was further confirmed by adding lanthanum trifluoroacetate [(TfO)3La], a strong Lewis acid, in the catalytic system (HCl, (TfO)3H, niobium phosphate), indicating that a suitable ratio of Lewis/Bronsted acid is important for higher selectivity to LA from HMF, as well as from cellulose. Then, after replacing N2 with H2, the generated LA in the reaction mixture can be directly converted to γ-valerolactone through hydrogenation over the Ru/C catalyst without further separation of LA.

Recent advances in the catalytic production of glucose from lignocellulosic biomass

Recently, research on the catalytic production of glucose, the first platform chemical in biorefinery, has become attractive in catalysis studies and the chemical/fuel industry owing to its broad applications. It opens up a new route for achieving sustainable chemical production and energy supply. From this viewpoint, this contribution attempts to overview the recent advances in the catalytic routes for the synthesis of glucose from lignocellulosic biomass over various homogeneous and heterogeneous catalysts.

Production of methyl levulinate from cellulose: selectivity and mechanism study

The alcoholysis of cellulose into methyl levulinate (ML) in methanol media was investigated in the presence of several kinds of acid catalyst. One of the synthesized solid niobium-based phosphate catalysts was found to be highly efficient for the generation of ML, reaching an ML yield as high as 56%, higher than the LA yield (52%) in aqueous solution with the same reaction conditions as those used in our previous study (Green Chem., 2014, 16, 3846–3853). More interestingly, in water, very strong Lewis acid promoted the formation of LA; but in methanol, Bronsted acid enhanced the formation of ML. In-depth investigation showed that the mechanism and type of intermediates of cellulose alcoholysis in methanol were different from those in water and a high Bronsted/Lewis acid ratio (known as B/L acid ratio) of solid catalysts is needed to prevent the generation of by-products, namely, methyl lactate and 1,1,2-trimethoxyethane. This new-proposed reaction mechanism affected by the B/L acid ratio was very helpful for the design of efficient catalysts.

Selective One‐Pot Production of High‐Grade Diesel‐Range Alkanes from Furfural and 2‐Methylfuran over Pd/NbOPO4

A one-pot method for the selective production of high-grade diesel-range alkanes from biomass-derived furfural and 2-methylfuran (2-MF) was developed by combining the hydroxyalkylation/alkylation (HAA) condensation of furfural with 2-MF and the subsequent hydrodeoxygenation (HDO) over a multifunctional Pd/NbOPO4 catalyst. The effects of various reaction conditions as well as a variety of solid-acid catalysts and metal-loaded NbOPO4 catalysts were systematically investigated to optimize the reaction conditions for both reactions. Under the optimal reaction conditions up to 89.1 % total yield of diesel-range alkanes was obtained from furfural and 2-MF by this one-pot method.

Energy-efficient production of 1-octanol from biomass-derived furfural-acetone in water

An energy-efficient catalytic system for the one-pot production of 1-octanol from biomass-derived furfural-acetone (FFA) under mild conditions in water was developed, by sequential hydrogenation/hydrogenolysis over a hydrophilic Pd/NbOPO4 catalyst. A strategy of creating an intentional “phase problem” has been employed to prevent the over-hydrogenolysis of 1-octanol into n-octane and therefore increased the selectivity to 1-octanol. The effects of reaction conditions as well as a variety of noble-metal loaded bifunctional catalysts have been systematically investigated to maximize the yield of 1-octanol. Moreover, the addition of liquid acids to the catalytic system further enhanced the selectivity towards the formation of 1-octanol. There is a strong correlation between the acid strength of an acidic additive and the sum yield of 1-octanol and octane. With the addition of TfOH, the highest yield of 1-octanol (62.7%) was obtained from one-pot conversion of biomass-derived FFA over Pd/NbOPO4.

Recent advances in heterogeneous catalytic conversion of glucose to 5-hydroxymethylfurfural via green routes

With concerns of diminishing fossil fuel reserves and environmental deterioration, great efforts have been made to explore novel approaches of efficiently utilizing bio-renewable feedstocks to produce chemicals and fuels. 5-Hydroxymethylfurfural (HMF), generated from dehydration of six-carbon ketose, is regarded as a primary and versatile renewable building block to realize the goal of production of these high valued products from renewable biomass resources transformation. In this review, we summarize the recent advances via green routes in the heterogeneous reaction system for the catalytic production of HMF from glucose conversion, and emphasize reaction pathways of these reaction approaches based on the fundamental mechanistic chemistry as well as highlight the challenges (such as separation and purification of products, reusing and regeneration of catalyst, recycling solvent) in this field.