Soluble Cello-Oligosaccharides Produced by Carbon-Catalyzed Hydrolysis of Cellulose

Cello-oligosaccharides are biologically important molecules that can elicit a defensive immune response in plants and improve the health of animals. Cellulose, a polymer of glucose linked by beta-1,4-glycosidic bonds, is an ideal feedstock for synthesis of cello-oligosaccharides. However, cello-oligosaccharides rapidly degrade under the conditions used for cellulose hydrolysis. Here, cellulose was hydrolyzed over a carbon catalyst in a semi-flow reactor to achieve a high yield of cello-oligosaccharides (72 %). The excellent activity of the oxidized carbon catalyst, the adsorption of cellulose on the catalyst, and the high space velocity of products in the reactor were essential. Moreover, a method for quantification of individual cello-oligosaccharides was developed, which suggested a reduction in the rate of hydrolysis with a reduction in chain length

Unraveling the hydrolysis of beta-1,4-glycosidic bonds in cello-oligosaccharides over carbon catalysts

Carbon catalysts having weakly acidic groups are uniquely active for hydrolysis of cellulose to produce cello-oligosaccharides and glucose. Although adsorption of cellulose molecules on carbon is considered as the cause for this behavior, the effect of adsorption on the reaction is not well understood. In order to understand the underlying mechanism, we investigated the hydrolysis of cello-oligosaccharides with varying chain lengths over different catalysts. Carbon catalysts favored hydrolysis of larger oligosaccharides with an 11-fold increase in the reaction rate constant from cellobiose to cellohexaose. The activation energy required to cleave the glycosidic bonds was reduced concurrently with the increase in molecule size. Based on these data, in conjugation with the stronger affinity of adsorption for larger oligosaccharides, we propose that axial adsorption within the micropores of carbon causes conformational change in the structure of cello-oligosaccharide molecules, resulting in reduction of activation energy required to cleave the beta-1,4-glycosidic bonds. Consequently, this translates to the higher rate of reaction for larger cello-oligosaccharides and explains the high reactivity of carbon catalysts towards cellulose hydrolysis

Study on crystal growth of Ge/Si quantum dots at different Ge deposition by using magnetron sputtering technique

Abstract We investigated the growth and evolution of Si-based Ge quantum dots (Ge/Si QDs) under low Ge deposition (1.2–4.4 nm thick) using magnetron sputtering. The morphology and structure of QDs were analyzed with the help of an atomic force microscope (AFM), scanning electron microscope, transmission electron microscope, Raman, surface energy theory and dynamics theory, the photoelectric properties of QDs were characterized by photoluminescence (PL) spectra. The results showed that the growth mechanism of QDs conformed to Stranski–Krastanow mode, but the typical thickness of the wetting layer was nearly three times higher than those derived from conventional technologies such as molecular beam epitaxy, chemical vapor deposition, solid phase epitaxy and so on. Meanwhile, the shape evolution of QDs was very different from existing reports. The specific internal causes of these novel phenomena were analyzed and confirmed and reported in this paper. In addition, the AFM, Raman, and PL tests all indicated that the QDs grown when 3.4 nm Ge was deposited have the most excellent morphology, structure, and optoelectronic performance. Our work lays a foundation for further exploration of the controllable growth of QDs at high deposition rates, which is a new way to realize the industrialization of QDs used for future devices

Catalytic depolymerization of the hydrolyzed lignin over mesoporous catalysts

In this work, the mesoporous SBA-15 and a series of modified catalysts based on it, such as Al-SBA-15 and Ni/Al-SBA-15, were synthesized and used for eliminating the char formation during the depolymerization of hydrolyzed lignin. The temperature, time and solvent effects on the lignin depolymerization were also investigated. Results showed that the repolymerization was effectively suppressed over SBA-15 due to its well-ordered pore structure and large pore size. The addition of Al and Ni elements in SBA-15 could improve the lignin depolymerization performance and saturate the instable intermediates. Ethanol was found to be more effective in suppressing repolymerization than other solvents. 81.4% liquefaction degree and 21.90 wt% monomer yield was achieved, and no obvious char was observed after the depolymerization of hydrolyzed lignin in ethanol solvent at 300 degrees C for 4 h over Ni/Al-SBA-15(20) catalyst. (C) 2016 Elsevier Ltd. All rights reserved

Synergistic effects of highly active Ni and acid site on the hydrodeoxygenation of syringol

The hydrodeoxygenation of syringol was explored with novel step by step precipitated Ni/SiO2-Al2O3 catalyst under mild conditions. Demethoxylation and dehydroxylation occurred in the first step, followed by the hydrogenation of benzene. Cyclohexane was formed eventually. Ni/SiO2-Al2O3 catalyst possessed high nickel dispersion and high amounts of acid sites. The synergistic effects of highly active Ni and acid site were the key to realize the occurrence of deoxygenation. These specialties resulted in the complete conversion of syringol at 200 degrees C, with the cyclohexane selectivity up to 97.8%, much better than the hydrodeoxygenation performances of single Ni/SiO2 and Ni/Al2O3. (C) 2016 Published by Elsevier B.V

Mild Hydrogenation of Lignin Depolymerization Products Over Ni/SiO2 Catalyst

Many efficient methods have been proposed to realize lignin depolymerization, while effective usage of lignin depolymerization products at mild conditions is still a big challenge. Conversion of them to stable products in thermal and chemical properties is a necessary step. Herein, a mild hydrogenation process of lignin depolymerization products over Ni/SiO2 catalyst was proposed. Model compound of 2,3-dihydrobenzofuran exhibited a good reaction result. Nearly 100% conversion was obtained at 130 degrees C, and the selectivity of 2-ethylcyclohexanol product reached 94.6%. The lignin depolymerization products also had a good hydrogenation result, in which not only the hydrogenation of unsaturated groups but also the cleavage of beta-O-4 bonds occurred. Stable products in thermal and chemical properties were formed, which possessed high heated value and low molecular weight. This treatment is conducive to suppressing the occurrence of condensation and favorable for the further catalytic conversion

Insight into the solvent, temperature and time effects on the hydrogenolysis of hydrolyzed lignin

The aim of this study is to explore the reaction mediums and conditions for producing high yield of valuable monomers from concentrated sulfuric acid hydrolyzed lignin. The solvent, temperature and time effects on the hydrogenolysis of hydrolyzed lignin were investigated under the catalysis of Pd/C and CrCl3. Supercritical methanol exhibits the best depolymerization performance, because of its unique diffusion, dissolution and acid-base properties. Afterwards, the influence of reaction temperature and time on depolymerization, repolymerization and coking during hydrogenolysis was examined in methanol. The high temperature is found to favor the depolymerization, with the beta-O-4 linkages cleaved significantly. However, the repolymerization is promoted simultaneously, and a high amount of beta-beta groups form. These reactions are in constant competition with each other and the repolymerization is preferred at excessive high temperature, producing bulk char residues, that is coking. This study will provide a beneficial reference for the maximization of lignin waste valorization. (C) 2016 Elsevier Ltd. All rights reserved

Hydrogenolysis process for lignosulfonate depolymerization using synergistic catalysts of noble metal and metal chloride

A novel hydrogenolysis process for lignosulfonate depolymerization was proposed using a noble metal catalyst cooperated with metal chloride in methanol. Hydrogenolysis performance was significantly affected by the catalysts, via a synergistic catalytic effect between the Lewis acid (metal chloride) and the noble metal. Reaction conditions were also optimized, with 8.6% aliphatic alcohols and 9.2% monomers obtained at 280 degrees C for 5 h over Pt/C cooperated with CrCl3. Analysis of the depolymerized products indicated that CrCl3 had a catalytic promoting effect on cleavage of beta-O-4 bonds with the synergistic catalytic effect of Pt/C. Meanwhile, the noble metal catalysed saturation of the depolymerized products and suppressed them from condensing into residues. The sulfonic groups of lignosulfonate were cleaved and they did not cause Pt/C poisoning. The catalyst showed good recyclability, with no significant loss of catalytic activity after three runs