The development of sustainable techniques to convert lignocellulosic materials into value-added chemicals remains a significant challenge. Herein, we report a novel technique to directly convert wheat straw to furan compounds, bio-oils, and phosphate fertilizers. Untreated wheat straw was initially converted into 5-hydroxymethylfurfural (HMF) and furfural in a biphasic reaction system using FePO4 and NaH2PO4 as co-catalyst. The remaining FePO4 in the solid residues was used as the catalyst to pyrolyze the solid residues, producing bio-oils and bio-char-based phosphate fertilizers. This combination of FePO4 and NaH2PO4 co-catalyst exhibited higher selectivity towards HMF and furfural production than using only FePO4 as a catalyst in the conversion of wheat straw. The maximum HMF yield, 44%, was obtained when the reaction was carried out at 160 °C for 60 min, while the highest furfural yield, 92%, was achieved when the reaction occurred at 150 °C for 60 min. This reaction system is one of the most effective reaction systems to date for the conversion of wheat straw. Excessive Brønsted or Lewis acid sites (Fe ions) cannot give high yields of HMF and furfural due to the formation of by-products, indicating that a synergistic combination of Brønsted and Lewis acid sites is critical to obtain high yields of furan compounds. Interestingly, FePO4 could effectively catalyze the pyrolysis of unconverted cellulose into new compounds, such as 5-methylfuran and 2,5-methylfuran, which is not observed in non-catalyzed pyrolysis.

•Under the optimized conditions, yield of fructose higher than 20% were obtained.•Fe/β zeolite catalysts maintained a constant catalytic activity after five consecutive cycles.•Isolated Fe species can be acted as active sites for glucose isomerization into fructose.Herein, the environmentally friendly Fe/β zeolite for glucose isomerization to fructose in aqueous media was reported for the first time. The effects of various reaction conditions including reaction temperature, reaction time, catalyst dosage, etc. on the isomerization reaction over Fe/β zeolite were studied in detail. Under the optimized conditions, yield of fructose higher than 20% were obtained. Moreover, the Fe/β zeolite catalysts were stable and remained constant catalytic activity after five consecutive runs. The possible active Fe species for isomerization of glucose in Fe/β zeolite is also discussed.Download high-res image (222KB)Download full-size image

•A cheap FePO4 catalyst was used to convert cellulose into 5-HMF.•A 5-HMF yield up to 49.5 mol% starting with cellulose was achieved.•The catalyst is readily recovered by precipitation after the reaction.•Soluble iron species derived from the hydrolysis reaction of FePO4 are responsible for the conversion of cellulose.It is of great significance to explore and develop a cost-effective and environmentally friendly way to covert cellulosic materials into 5-hydroxymethylfurfural (5-HMF). An inexpensive FePO4 catalyst, which is insoluble at room temperature but can be partially dissolved and behaves as homogeneous catalyst at elevated temperatures, was used to directly convert cellulose into 5-HMF. The effect of various reaction conditions including reaction temperature, reaction time, cellulose concentration and catalyst amount on the conversion of cellulose and 5-HMF yield was investigated. A 5-HMF yield up to 49.5 mol% was achieved at 160 °C for 60 min with the FePO4 catalyst, which is comparable to the highest yield of 5-HMF obtained in ionic liquid or homogeneous catalysis reaction systems. Moreover, this unique catalyst is readily separated from the aqueous solution via precipitation after cooling to room temperature since it is insoluble at room temperature. The catalyst can be used over five successive cycles although the amorphous FePO4 underwent the structural transformation from an amorphous phase into a new crystalline form of FePO4, evidenced by XRD, IR, and visible Raman spectroscopic results. The soluble iron species, such as Fe3 + species, act as Lewis acid sites catalyzing isomerization of glucose to fructose followed by the dehydration of fructose into 5-HMF catalyzed by H+ ions.

The highly efficient synthesis of 5-hydroxymethylfurfural (HMF) from carbohydrates was achieved using the inexpensive and bi-functional CrPO4 catalyst in a biphasic system. The effect of various reaction conditions, including reaction temperature, time, and solvent, on HMF yields was explored. A HMF yield of up to 83% was obtained using fructose as the reactant at 140 °C for 15 min. A maximum HMF yield of 63% was also achieved from glucose when the reaction was carried out at 140 °C for 30 min. Among the reported catalysts, CrPO4 was shown to be one of the most effective in the conversion of glucose into HMF, which is comparable to an ionic liquid reaction system. Moreover, the CrPO4 catalyst exhibited high activity to convert microcrystalline and lignocellulosic feedstock to HMF without the need for the addition of homogeneous mineral acids. The possible conversion mechanism of carbohydrates into HMF catalyzed by the bi-functional CrPO4 catalyst is discussed.

Catalytic conversion of carbohydrates to 5-hydroxymethylfurfural (5-HMF) provides a way toward obtaining renewable biomass-based fuels and chemicals. Herein, we use an inexpensive FePO4 catalyst, which is insoluble at low temperature but can be partially dissolved and act as a homogeneous catalyst at high temperature, in a one-vessel biphasic reactor to generate 5-HMF from carbohydrates such as fructose, glucose, sucrose, cellulose, and Camellia oleifera shell (a lignocellulosic feedstock) without the addition of homogeneous acids. The effects of various reaction conditions including reaction temperature, reaction time, feedstock types and the amount of catalyst on fructose conversion and 5-HMF yield were investigated. The highest 5-HMF yield (71.5 mol%) starting from fructose feedstock was achieved using this “one-pot” biphasic water/tetrahydrofuran (THF) reactor system at 140 °C for 15 min. More interestingly, at high temperature, the FePO4 catalyst was also highly active in the conversion of cellulose and Camellia oleifera shell, which are very difficult to convert to 5-HMF without the addition of mineral acids. A high 5-HMF yield of 48 mol% starting from microcrystalline cellulose was also obtained using the biphasic reaction system. Moreover, the FePO4 catalyst could be easily separated and recycled from the aqueous solution via precipitation after cooling to room temperature since it is insoluble at low temperature. Possible dehydration reaction mechanisms of these carbohydrates catalyzed by FePO4 were also proposed.

•A direct catalytic conversion of cellulose to EG and 1,2-PG was achieved on Pt/CNTs.•Highly dispersed Pt/CNTs catalysts with particle size less than 5 nm were prepared.•The total yields of up to 71.4% for EG and 1,2-PG were obtained.•A conversion pathway of cellulose to EG and 1,2-PG was proposed.A series of Pt nanoparticles supported on carbon nanotubes (CNTs) were synthesized using the incipient-wetness impregnation method. These catalysts were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman spectroscopy, and transmission electron microscope (TEM) techniques. The characterization results indicate that the Pt nanoparticles were highly dispersed on the surface of the CNTs, and the mean size was less than 5 nm. These catalysts were utilized to convert cellulose to hexitol, ethylene glycerol (EG), and 1,2-propylene glycol (1,2-PG) under low H2 pressure. The total yields were as high as 71.4% for EG and 1,2-PG using 1 Pt/CNTs as the catalyst in the hydrolytic hydrogenation of cellulose under mild reaction conditions.

In this work, Zn/ZSM-5 zeolite catalysts with different Zn contents are prepared by impregnation method. The influences of reaction temperature and time, catalyst dosage and the acidic properties of catalysts on the conversion of γ-valerolactone to aromatic compounds are investigated. The results show that the introduction of Zn into H-ZSM-5 channel could effective modify the components of liquid product and influence the yields of gas, liquid and solid as compared to H-ZSM-5 catalyst and non-catalytic conversion of γ-valerolactone. Zn/ZSM-5 catalyst affords the higher contents of aromatic compounds compared to H-ZSM-5 and silica catalysts in the liquid product under identical reaction conditions. Therefore, Zn species of Zn/ZSM-5 can not only effectively improve the conversion of γ-valerolactone, but also enhance the formation of aromatic compounds, suggesting that Zn species play a key role in the formation of these aromatic compounds.