Alloying nickel and cobalt with iron on ZSM-5 for tuning competitive hydrogenation reactions for selective one-pot conversion of furfural to gamma-valerolactone.

One-pot conversion of furfural, a biomass-derived platform chemical, to gamma-valerolactone (GVL), a fuel additive and green solvent, involves multiple steps of hydrogenation. Among these reactions, the deep hydrogenation of the furan ring in furfural interrupts GVL formation over Ni or Co-based catalysts. In this study, a method of alloying Ni and Co with Fe over a ZSM-5 support was proposed for tackling excessive activity of the catalyst for hydrogenation. The results indicated that the formation of binary NiFe and CoFe alloys in Ni-Co-Fe/ZSM-5 enhanced the dispersion of metallic species, reduction of metal oxides, formation of more Lewis acidic sites, and the adsorption of the C-O functionality of the furan ring, while lowering the capability for adsorption/activation of H2 and the adsorption of the CC group of the furan ring. These factors together reduced the activity for the hydrogenation of the furan ring in furfural, but enhanced the hydrogenation of the CO in ethyl levulinate (EL). The kinetic study confirmed that the hydrogenation of EL was the rate-determining step. The coordination of the dual alloys, NiFe and CoFe, in the bifunctional Ni-Co-Fe/ZSM-5 catalyst rendered superior activity for selective one-pot conversion of furfural to GVL with a yield of 85.7%.

Pyrolysis of cellulose: Correlation of hydrophilicity with evolution of functionality of biochar.

Biochar is a carbonaceous material from pyrolysis of biomass, the application of which is governed by its various properties such as the distribution of the functionalities and the associated hydrophilic/hydrophobic nature. This study particularly focused on the correlation of functionalities of biochar with its polarities by conducting the pyrolysis of cellulose from 200 to 700 °C and the characterization of the biochar. The results demonstrated that -OH, instead of CO or C-O-C, played decisive roles in formation of the biochar with hydrophilic surface. The results showed that the maximum of -OH abundance and the aliphatic CH was reached at 440 °C. The significant transition of oxygen-rich functionalities to carbon-rich functionalities occurred in the temperature from 460 to 700 °C. The dominance of aromatization process above this temperature range resulted in the significant increase of hydrophobicity of the biochar. The hydrophilic surface was of importance for the use of biochar as support for promoting the dispersion of Cu in Cu/biochar by generating the bonding sites for chelating with Cu2+.

Crystal facet-dependent activity of h-WO3 for selective conversion of furfuryl alcohol to ethyl levulinate.

The use of WO3 as an acid catalyst has received extensive attention in recent years. However, the correlation between the catalytic activity and the predominantly exposed surface with varied acidic sites needs further understanding. Herein, the effects of the Brønsted and Lewis acid sites of different crystal facets of WO3 on the catalytic conversion of furfuryl alcohol (FA) to ethyl levulinate (EL) in ethanol were investigated in detail. A yield of EL up to 93.3% over WO3 with the (110) facet exposed was achieved at 170 °C, while FA was mainly converted to polymers over (001) faceted nanosheets and nanobelts with exposed (002) and (100) facets. This was attributed to the different distribution of the acidic sites on different exposed crystal facets. The (110) faceted WO3 possessed abundant and strong Brønsted acid sites, which favored the conversion of FA to EL, while the (100) faceted WO3 with stronger Lewis acid sites and weaker Brønsted acid sites mainly led to the formation of polymers. In addition, the (110) faceted WO3 showed excellent sustainability in comparison with the (100) faceted counterpart.

Impacts of temperature on evolution of char structure during pyrolysis of lignin.

This study investigated the pyrolysis of lignin pyrolysis in a temperature region from 200 to 800 °C, aiming to understand influence of pyrolysis temperature on evolution of structures of the resulting char. The results showed that fusion of the ring structure initiated at 200 °C, where the C/H ratio in the char was equal to that in naphthalene (two fused rings). The C/H ratio in the char obtained at 350 °C corresponded to that in pyrene (four fused rings), while the char produced at 550 °C was equivalent to 20 fused benzene rings in terms of C/H ratio. The increasing pyrolysis temperature also shifted the oxygen-containing functionalities such as the carbonyl, esters, ketones in the bio-oil to the ether functionality that had a higher thermal stability. The DRIFTS study of pyrolysis of lignin showed that drastic changes of the functionalities and the internal structure of the char occurred in a narrow temperature region from 520 to 530 °C. The carbonyl functionality and the aliphatic structure were eliminated, and new conjugated π-bond systems formed.

Dewatering of sewage sludge via thermal hydrolysis with ammonia-treated Fenton iron sludge as skeleton material.

In this study, the alkaline hydrothermal ferric carbon (AHFC), which was prepared by hydrothermal liquefaction method using Fenton iron sludge with NH3·H2O, was used as a skeleton materials for the dewatering of sewage sludge (SS) via thermal hydrolysis. NH2 functional group presented in the AHFC and nano-sized γ-Fe2O3 was anchored on the surface of AHFC. The NH2 functional group notably promoted thermal hydrolysis of SS from the increasing of TOC and TN value. γ-Fe2O3 showed adsorption effect to the water, resulting in decline of the dewatering rate of SS in present condition. When 100% of AHFC was added, dewatering rate of SS was decreased by 19.93% (at 160 °C), 4.50% (at 180 °C) and 8.34% (at 200 °C) respectively. 3D-EEM results showed that the degree of hydrolysis was deepened when AHFC was added for the intensity of soluble microbial products decline. AHFC promoted the decomposition of protein to form heterocycle compounds in the resulting cake according to in situ FTIR results. The nano γ-Fe2O3 catalysis to cake also can be observed for the activation energy was lower than blank in the range of 40˜60%. The study demonstrated concept and the effectiveness the reuse/recycle of the Fenton iron sludge for dewatering of SS.

Structural differences of the soluble oligomers and insoluble polymers from acid-catalyzed conversion of sugars with varied structures.

In this paper, acid-catalyzed conversion of nine sugars (xylose, glucose, fructose, galactose, sucrose, maltose, lactose, raffinose, and ß-cyclodextrin) with different sizes, steric structures and functionalities were investigated and impacts of the varied sugars on structures of resulting polymers were focused. Under similar reaction conditions, the yields of the carbon materials (insoluble polymers) formed followed the order: xylose ¼ lactose > galactose > ß-cyclodextrin > maltose > sucrose > fructose > glucose > raffinose. Increasing temperature enhanced transformation of soluble oligomers into insoluble ones. Morphologies of the carbon materials were closely related to sugar structures. Diameters of carbon materials (microsphere form) obtained from the disaccharides and oligosaccharides were larger than that of monosaccharides. Furthermore, the microspheres from oligosaccharides had a higher affinity to each other, resulting from continued polymerization as some reactive functionalities were retained in carbon materials. In addition, graphite structure was formed in the carbon materials, even at 160 °C.

Hydrothermal liquefaction of cellulose in ammonia/water.

In order to obtain the N-containing organics from cellulose under mild conditions, hydrothermal liquefaction of cellulose in the presence of ammonia was conducted in this study. The results showed that the increasing reaction temperature and prolonging time facilitated the conversion of cellulose in hydrothermal liquefaction (HTL) with NH3·H2O and decreased the amount of solid residue. Reaction temperature showed more influence than reaction time on solid residue formation. The components of bio-oil were significantly affected by reaction temperature and reaction time. Electrospray ionization-Fourier transform-ion cyclotron resonance-mass spectrometry (ESI FT-ICR MS) provided an insight for understanding the distribution of the different kinds of N-heterocycle compounds in the bio-oil. The possible reaction pathway of N-heterocycle compounds formation from cellulose during hydrothermal liquefaction with NH3·H2O was proposed.