Decomposition of lignin model compounds by Lewis acid catalysts in water and ethanol

The conversion of benzyl phenyl ether, diphenyl ether, diphenyl methane and biphenyl as representative model compounds for a–O4, 5–O4, a 1 (methylene bridges) and 5–5' lignin linkages was investigated. We compared the use of metal chlorides and acetates. The reactions were studied in sub- and supercritical water and supercritical ethanol between 300-400 °C. At low temperature in water, Lewis acids mainly catalyzed condensation of hydrolysis products of the dimeric model compounds. At higher temperature, mono-aromatic products were formed. The yield of monomeric products was higher in ethanol than in water. The preference for ethanol is due to extensive alkylation of the mono-aromatic products, which inhibits their condensation into larger products. The highest yields of deoxygenated mono-aromatics were obtained using Lewis acid catalysts at 400 °C in supercritical ethanol. The preferred Lewis acid catalysts were Fe, Cu, Ni and Al chlorides

Lewis acid-catalyzed depolymerization of soda lignin in supercritical ethanol/water mixtures

The depolymerization of lignin model compounds and soda lignin by super Lewis acidic metal triflates has been investigated in a mixture of ethanol and water at 400 °C. The strong Lewis acids convert representative model compounds for the structure-forming linkages in lignin, namely a–O–4, 5–O–4 (C–O–C ether bridge), and a–1 (methylene bridge). Only the 5–5' C–C linkage in biphenyl was unaffected under the given reaction conditions. Full conversion of soda lignin was achieved without char formation. Lignin was converted into a wide range of aliphatic and aromatic hydrocarbons. Ethanol was involved in the alkylation of the lignin depolymerization products. These alkylation reactions increased the product yield by inhibiting repolymerization of the products. The resulting organic phase consisted of aliphatic hydrocarbons (paraffins and olefins), aromatic hydrocarbons (extensively alkylated non-oxygenated mono-aromatics, mainly alkylbenzenes as well as mono-aromatic oxygenates, mainly phenolics), condensation products (mainly naphthalenes) and saturated oxygenates (ketones and carboxylic acids). Although complete product analysis was not possible, the data suggest that the dominant fraction of lignin was converted into monomeric units with a small fraction with molecular weights up to 650 g/mol

Hollow core mesoporous shell carbon supported Pt electrocatalysts with high Pt loading for PEMFCs

The aim of this study is to synthesize mesoporous carbon supports and prepare their corresponding electrocatalysts with microwave irradiation method and also increasing the Pt loading over the carbon support by using some additional reducing agents. Pt loadings on hollow core mesoporous shell (HCMS) and commercial Vulcan XC72 carbon supports up to 34% and 44%, respectively, were achieved via polyol process with microwave irradiation method. When hydrazine or sodium borohydride was used in addition to ethylene glycol, Pt loading over the HCMS carbon support was increased. Characterization of the prepared electrocatalysts was performed by ex situ (BET, XRD, SEM, TGA and Cyclic Voltammetry) and in situ (PEM fuel cell tests) analysis. PEM fuel cell performance tests showed that 44% Pt/Vulcan XC72 and 28% Pt/HCMS electrocatalysts exhibited improved fuel cell performances. The results revealed that as the Pt loading increased PEM fuel cell performance was also increased. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved

Hydrodeoxygenation of mono- and dimeric lignin model compounds on noble metal catalysts

The influence of reaction conditions (temperature, acidity) on the catalytic performance of supported Pt, Pd and Ru catalysts for the aqueous phase hydrodeoxygenation (HDO) of lignin model compounds was systematically investigated. Phenol conversion proceeds via hydrogenation of the aromatic ring resulting in cyclohexanone, which is subsequently converted to cyclohexanol and cyclohexane. Although aromatic ring hydrogenation has a higher rate for Pt and Pd-based catalysts, the rate of hydrogenation of the polar C=O moiety in cyclohexanone is faster for Ru/C. The complete HDO of phenol to cyclohexane on noble-metal catalysts can only be achieved in the presence of a Brønsted acid co-catalyst. In guaiacol conversion, efficient demethoxylation and ring hydrogenation can be achieved within 0.5 h on Pt/C. Under acidic conditions, selectivity of nearly 90% to cyclohexane at a conversion of 75% was achieved in 4 h. To get an insight into the possibility to cleave covalent linkages between aromatic units in lignin under HDO conditions, the reactivity of dimeric model substances such as diphenyl ether, benzyl phenyl ether, diphenyl methane and biphenyl was investigated. Although dimeric oxygen-bridged model compounds such as benzylphenyl ether and diphenyl ether can be readily converted to monomeric species in the presence of noble metal catalysts, cleavage of C–C bonds in diphenyl methane and biphenyl was not observed. Plausible reaction mechanisms are proposed

Parasite-induced alteration of plastic response to predation threat: increased refuge use but lower food intake in Gammarus pulex infected with the acanothocephalan Pomphorhynchus laevis.

6 pagesInternational audienceLarvae of many trophically-transmitted parasites alter the behaviour of their intermediate host in ways that increase their probability of transmission to the next host in their life cycle. Before reaching a stage that is infective to the next host, parasite larvae may develop through several larval stages in the intermediate host that are not infective to the definitive host. Early predation at these stages results in parasite death, and it has recently been shown that non-infective larvae of some helminths decrease such risk by enhancing the anti-predator defences of the host, including decreased activity and increased sheltering. However, these behavioural changes may divert infected hosts from an optimal balance between survival and foraging (either seeking food or a mate). In this study, this hypothesis was tested using the intermediate host of the acanthocephalan parasite Pomphorhynchus laevis, the freshwater amphipod Gammarus pulex. We compared activity, refuge use, food foraging and food intake of hosts experimentally infected with the non-infective stage (acanthella), with that of uninfected gammarids. Behavioural assays were conducted in four situations varying in predation risk and in food accessibility. Acanthella-infected amphipods showed an increase in refuge use and a general reduction in activity and food intake. There was no effect of parasite intensity on these traits. Uninfected individuals showed plastic responses to water-borne cues from fish by adjusting refuge use, activity and food intake. They also foraged more when the food was placed outside the refuge. At the intra-individual level, refuge use and food intake were positively correlated in infected gammarids only. Overall, our findings suggest that uninfected gammarids exhibit risk-sensitive behaviour including increased food intake under predation risk, whereas gammarids infected with the non-infective larvae of P. laevis exhibit a lower motivation to feed, irrespective of predation risk and food accessibility

Hydrodeoxygenation of mono- and dimeric lignin model compounds on noble metal catalysts

The influence of reaction conditions (temperature, acidity) on the catalytic performance of supported Pt, Pd and Ru catalysts for the aqueous phase hydrodeoxygenation (HDO) of lignin model compounds was systematically investigated. Phenol conversion proceeds via hydrogenation of the aromatic ring resulting in cyclohexanone, which is subsequently converted to cyclohexanol and cyclohexane. Although aromatic ring hydrogenation has a higher rate for Pt and Pd-based catalysts, the rate of hydrogenation of the polar C=O moiety in cyclohexanone is faster for Ru/C. The complete HDO of phenol to cyclohexane on noble-metal catalysts can only be achieved in the presence of a Bronsted acid co-catalyst. In guaiacol conversion, efficient demethoxylation and ring hydrogenation can be achieved within 0.5 h on Pt/C. Under acidic conditions, selectivity of nearly 90% to cyclohexane at a conversion of 75% was achieved in 4h. To get an insight into the possibility to cleave covalent linkages between aromatic units in lignin under HDO conditions, the reactivity of dimeric model substances such as diphenyl ether, benzyl phenyl ether, diphenyl methane and biphenyl was investigated. Although dimeric oxygen-bridged model compounds such as benzylphenyl ether and diphenyl ether can be readily converted to monomeric species in the presence of noble metal catalysts, cleavage of C-C bonds in diphenyl methane and biphenyl was not observed. Plausible reaction mechanisms are proposed. (C) 2013 Elsevier B.V. All rights reserved

Lewis-acid catalyzed depolymerization of Protobind lignin in supercritical water and ethanol

The use of metal acetates, metal chlorides and metal triflates as Lewis acid catalysts for the depolymerization of soda lignin under supercritical conditions was investigated. The reactions were carried out at 400 degrees C in water and ethanol. Lignin conversion in supercritical water led to formation of insoluble char and resulted in low yields of monomeric products. When the reaction was performed in supercritical ethanol, char formation was inhibited and higher yields of low molecular-weight organic products were obtained. The ethanol solvent was also converted in two ways. Firstly, the lignin depolymerization products were alkylated by ethanol. Secondly, ethanol was converted into a range of higher hydrocarbons including paraffins and olefins. Possible mechanisms of the lignin and ethanol conversion reactions are discussed. (C) 2015 Elsevier B.V. All rights reserved

Decomposition of lignin model compounds by Lewis acid catalysts in water and ethanol

The conversion of benzyl phenyl ether, diphenyl ether, diphenyl methane and biphenyl as representative model compounds for alpha-O-4, 5-O-4, alpha(1) (methylene bridges) and 5-5' lignin linkages was investigated. We compared the use of metal chlorides and acetates. The reactions were studied in sub- and supercritical water and supercritical ethanol between 300 and 400 degrees C. At low temperature in water, Lewis acids mainly catalyzed condensation of hydrolysis products of the dimeric model compounds. At higher temperature, mono-aromatic products were formed. The yield of monomeric products was higher in ethanol than in water. The preference for ethanol is due to extensive alkylation of the mono-aromatic products, which inhibits their condensation into larger products. The highest yields of deoxygenated mono-aromatics were obtained using Lewis acid catalysts at 400 degrees C in supercritical ethanol. The preferred Lewis acid catalysts were Fe, Cu, Ni and Al chlorides. (C) 2015 Elsevier B.V. All rights reserved