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In this study, microwave irradiation is employed for the phenolation of acid-insoluble Klason lignin. Microwave irradiation significantly reduces the reaction temperature (180 → 100 °C) and time (6 h → 10 min) without noticeable differences in the chemical structure of the phenolated lignin compared with the products prepared using a conventional heating method. As the reaction temperature increases (100 → 150 °C), lignin decomposition and crosslinking occur simultaneously, as did phenolation. Upon increasing the phenol-to-lignin ratio, the fragmentation of lignin is enhanced, while the crosslinking reaction is inhibited, leading to a decrease in the molecular weight and glass transition temperature of the phenolated lignin. Density functional theory is applied to elucidate the thermal and non-thermal effects of the electromagnetic field on the phenolation of Klason lignin. The solubility of Klason lignin in tetrahydrofuran and methanol is highly enhanced after phenolation, which allows for its adhesive application on glass, polyethylene naphthalate, and polyimide substrates. [ABSTRACT FROM AUTHOR]

In this study, we explored the catalytic hydrocracking of pyrolytic lignin (PL) under supercritical methanol conditions. This approach aimed to minimize coke formation and prevent solidification of bio-oil, thus improving its manageability and upgrade potential in subsequent steps. Hydrocracking of PL at 250°C for 2 h with HZSM-5, Ni/HZSM-5, and Ni-Ru/HZSM-5 catalysts revealed a dominance of repolymerization over hydrocracking. Consequently, the methanol-soluble oil portion decreased to <37.8 wt%, accompanied by an increase in product molecular weight. However, by co-depositing Ni and Ru on ceria-impregnated HZSM-5 catalysts, the yield of methanol-soluble oil increased to 48.5–56.1 wt%, while the molecular weight decreased. By optimizing reaction parameters using Ni-Ru/Ce-HZSM-5 (NRC4H) at 300°C for 1 h, a methanol-soluble yield of 52.5 wt% was achieved, along with a substantial reduction in molecular weight. The interaction of Ni, Ru, and Ce elements on the catalyst's acidic surface led to smaller Ni and Ru particles and improved reducibility, resulting in a suitable acid-base balance that effectively suppressed repolymerization and enhanced hydrocracking. Furthermore, the detection of methane in the gas product served as an indicator of the hydrogenation reaction of double bonds during the hydrocracking process. • Bimetallic Ni Ru catalyst showed higher yields of methanol-soluble compounds. • Ce deposition in Ni-Ru/HZSM5 impacted dispersion of metals and catalyst properties. • Methane formation was a descriptor for Ni-catalyzed olefin hydrogenation. [ABSTRACT FROM AUTHOR]

Lignin is a natural polymer contained in lignocellulose and is a potential feedstock for the production of phenolics or small aromatic molecules. However, lignin depolymerization is typically performed using low lignin concentrations and insufficiently active catalysts, which hinders industrial applications. To address this issue, we herein investigated the depolymerization of concentrated kraft lignin and oak-extracted organosolv lignin promoted by supported bifunctional metal (palladium)-acid catalysts and elucidated the roles of acid and metal sites. In addition to acid sites, which are known to be critical for lignin degradation, metal sites were found to be required to initiate lignin depolymerization. Palladium atoms promoted depolymerization even in the absence of acid sites, while acid site–promoted depolymerization required the presence of surface palladium atoms. Catalysts with bulk palladium particles were much more active than those with highly dispersed palladium particles, which suggested that efficient depolymerization required the bulky lignin polymer to be adsorbed on the palladium surface in a multidentate fashion. Thus, our work provides valuable insights into the mechanism of catalytic lignin depolymerization and paves the way to the industrial-scale application of this process. [Display omitted] • Lignin depolymerization by bifunctional metal (Pd)-acid catalysts is studied. • Roles of acid and metal sites in this depolymerization are elucidated. • Bulk Pd particles are more active than highly dispersed Pd particles. • Depolymerization requires multidentate lignin adsorption on the Pd surface. [ABSTRACT FROM AUTHOR]

The production of cellulose-derived biofuels and biochemicals, such as bioalcohols and bioplastics, from lignocellulose requires the isolation of cellulose by lignin removal or delignification processes. While the remaining lignin and its phenolic fragments have been reported to inhibit the biological conversion of cellulose, we observed that the catalytic hydrolysis of cellulose also can be inhibited most likely because of an associative interaction between cellulose and lignin. The associative interaction between cellulose and the functional groups of lignin was proven by gel-permeation-chromatography measurement of regenerated mixtures of lignin and cellulose which simulate the lignocellulose-derived cellulose containing lignin as an impurity. Chemical bonds between cellulose and lignin were hypothesized using lignin model compounds containing known functionalities such as hydroxyl, methoxy, phenyl, allyl, and carboxyl groups in order to explain the effects of lignin on the hydrolysis of cellulose. The yield of glucose from cellulose dropped when carboxylic and hydroxyl groups were present possibly because of the formation of ether and ester bonds between the lignin and cellulose. These observations may help develop the chemical processes and therefore convert the inedible biomass resource of lignocellulose-based cellulose containing lignin and its derivatives to the valuable fuels and chemicals. [ABSTRACT FROM AUTHOR]

or sugar-derived compounds were used as environmentally friendly additives for the depolymerization of Kraft lignin waste and organosolv lignin prepared from Miscanthus giganteus. The yields of the aromatic monomers obtained from Kraft lignin increased from 5.1 to 49.2% with the addition of mannitol, while those obtained from organosolv lignin increased from 44.4 to 83.0% with the addition of sucrose. This improved lignin depolymerization was also confirmed by gel permeation chromatography and nuclear magnetic resonance spectroscopy. The above results clearly indicate the beneficial effects of carbohydrate derivatives on the lignin depolymersization process, more specifically, suggesting that the presence of carbohydrates improve the lignin depolymerization of lignocellulose, as observed for the raw lignocellulose feed. Image 1 • Carbohydrate-derived additives were used in the depolymerization of lignin. • The aromatic monomer yields from Kraft lignin and organosolv lignin increased. • Mannitol and sucrose were found to most improve the aromatic monomer yields. • Carbohydrates improved the lignin depolymerization of lignocellulose. • The improved depolymerization was confirmed by GPC and NMR studies. Main finding: The addition of carbohydrate derivatives improved the catalytic depolymerization of lignin waste to phenolic compounds. [ABSTRACT FROM AUTHOR]

A calcium carbonate (CaCO 3)-supported Ru catalyst (Ru/CaCO 3) prepared by a wet impregnation method was used for the hydrodeoxygenation (HDO) of eugenol, a lignin model compound representing coniferyl alcohols, and was shown to surpass Ru supported on neutral (ZrO 2) and basic supports (MgAlO x , hydrotalcite, and MgO) in terms of deoxygenation activity. The production of deoxygenated compounds was observed during the batch reduction of eugenol with H 2 (room-temperature-equivalent pressure = 50 bar) over Ru/CaCO 3 at 250 °C, and the yields of compounds with no oxygen atoms (0-O) and one oxygen atom (1-O) were determined as 25.5 and 48.2%, respectively. X-ray photoelectron spectroscopy revealed that the improved hydrodeoxygenation activity could be ascribed to the increased electron density of catalytically active Ru species because of electron donation from the support. Unlabelled Image • Ru/CaCO 3 as a base-supported metal catalyst for the upgrading of bio-oil. • Improvement of HDO performance by the presence of CaCO 3. • Electron rich Ru particles formed by CaCO 3. [ABSTRACT FROM AUTHOR]

The improved catalytic activity of Rh nanoparticles deposited on the swollen and pillared zeolites was observed in the hydrodeoxygenation (HDO) reactions of 1,3,5-trimethoxybenzene (1,3,5-TMB), a bulky lignin model compound, and guaiacol, one of the most frequently used lignin model compounds. As the high dispersion of metal nanoparticles increases HDO activity, the swelling/calcination and pillaring of crystalline MCM-22 zeolites increased the dispersion of Rh metal nanoparticles on the external surface area, and thus the corresponding HDO activity with respect to 1,3,5-TMB. On the contrary, although the mesopores in the amorphous MCM-41 and silica-alumina aerogel (SAA) supports accommodated higher Rh dispersion, overall, the resulting catalysts suffered from mass transfer limitation, and thus showed poor HDO reaction activity for 1,3,5-TMB. Finally, the Rh nanoparticles supported on the pillared zeolite showed the highest HDO activity for guaiacol, mainly due to the higher Rh dispersion and acid sites on the external surface among the zeolite-supported Rh catalysts. [ABSTRACT FROM AUTHOR]

• TiO 2 -supported Ni catalysts fabricated for selective hydrodeoxygenation (HDO) • Selective conversion of alkyl methoxyphenols to saturated cyclic alcohols achieved. • Strong metal-support interaction was tuned by adding Fe. TiO 2 -supported Ni catalysts are promising candidates that can be used to achieve biomass valorization following the selective hydrodeoxygenation (HDO). Their catalytic activity can be tuned and they are characterized by strong metal–support interaction (SMSI). The SMSI observed at the interfaces of Ni nanoparticles (NPs) and the TiO 2 support was tuned by adding Fe and subjecting the synthesis system to hydrothermal treatment conditions. The prepared catalysts promoted the selective conversion of alkyl methoxyphenols, including lignin-derived guaiacol, to saturated cyclic alcohols. The low Fe content (∼1.5 wt%) in Ni/TiO 2 significantly promoted the formation of cyclohexanol from guaiacol (rate: 183 mol cyclohexanol ·mol Ni −1·h−1; selectivity: 85%). Alkyl methoxyphenols present in the biomass pyrolysis oil could be effectively converted into cyclic alcohols (yield: 71%). It was observed that the interfacial sites of highly dispersed NiFe-FeO x core–shell structures on the TiO 2 support promote the demethoxylation of reactant to selectively produce cyclic alcohols. [ABSTRACT FROM AUTHOR]

• Lignin pyrolysis oil or lignin oil was hydrocracked to less-viscous liquid products. • Oligomers and oxygen functionalities were removed over CoMo/Hβ or CoMo/Al 2 O 3. • Low viscosity (3.2 cP), high yield (72.3%), and low coke yield (1.2%) were obtained. • Hydrocracked liquid dissolved lignin oil with the high solubility. • Continuous flow reaction was successful using lignin oil in hydrocracked liquid. The development of solvent-free lignin pyrolysis processes is highly desirable, because these processes would allow the depolymerized product to be used directly as a renewable energy source and chemical feedstock, without removal of solvnets. However, this product is typically highly viscous and cannot be used in continuous-flow reaction systems. In this study, lignin pyrolysis oil was prepared from Kraft lignin using bench-scale fixed-bed batch pyrolysis and then hydrocracked to produce less-viscous liquid products. Oligomers were degraded into smaller molecules via reactions involving hydrogen (hydrocracking) using CoMo/Hβ and CoMo/Al 2 O 3 as catalysts. A low viscosity of 21 cP, a liquid yield of 76.6%, and a low coke yield of 1.6% were successfully attained using a reaction temperature of 400 °C, a reaction time of 60 min, and the CoMo/Hβ catalyst. Thus, these conditions were selected to achieve the highest liquid yield with sufficient fluidity, although the lowest viscosity of 3.2 cP was achieved after 240 min. When 30 wt% of the resulting hydrocracked oil was used, it dissolved sticky raw lignin pyrolysis oil, significantly reducing its viscosity from 751 cP to 111 cP, which is sufficient to ensure flow in a typical petroleum pipeline. Using the hydrocracked/raw lignin pyrolysis oil mixture, the proposed continuous-flow hydrodeoxygenation successfully produced petroleum-replacing deoxygenated fuels. [ABSTRACT FROM AUTHOR]

Five carbon materials, including multi-walled carbon nanotubes (MWCNT), carbon aerogel (CARF), carbon black (Vulcan carbon), activated carbon (AC), and graphite, were used as supports of the carbon-supported Ru catalysts, and the hydrodeoxygenation of lignin-derived monomers and lignocellulose pyrolysis oil was performed. Ru/MWCNT exhibited the highest deoxygenation activity, and the origin of the improved catalytic activity was studied. The metal dispersion, the acidity as measured by means of temperature-programmed desorption, the pore structure, and the surface area were investigated in an effort to understand the catalysis results. We observed that the quantity of accessible Ru nanoparticles on the mesopores determined the hydrodeoxygenation activity. [ABSTRACT FROM AUTHOR]

Highlights: [•] Two-step catalysis of lignin dimer produced high carbon number cyclic hydrocarbons. [•] Isomerization of ether to alcohol without cracking was suggested. [•] Brönsted acids activated the catalytic isomerization of an α-O-4 compound. [•] NH3-TPD, pyridine-FT-IR, and NMR elucidated the active sites. [ABSTRACT FROM AUTHOR]

Abstract: Hydrodeoxygenation of the lignin monomer guaiacol was performed on the bifunctional catalysts of noble-metals supported on acidic matrices. The catalytic roles of metal nanoparticles and acidic supports were elucidated using the acid-site-measurement-dependent catalysis results, which demonstrated that metals were responsible for the hydrogenation of aromatic rings while metal-deposited acidic supports were indispensable to the deoxygenation of oxygenates. Among various combinations of metals and supports, Rh/SiO2-Al2O3 and Ru/SiO2-Al2O3 exhibited the highest cyclohexane yields. [Copyright &y& Elsevier]