The synthesis of high-efficiency and low-cost catalysts for hydrodeoxygenation (HDO) of waste lignin to advanced biofuels is crucial for enhancing current biorefinery processes. Inexpensive transition metals, including Fe, Ni, Cu, and Zn, were severally co-loaded with Ru on HY zeolite to form bimetallic and bifunctional catalysts. These catalysts were subsequently tested for HDO conversion of softwood lignin and several lignin model compounds. Results indicated that the inexpensive earth-abundant metals could modulate the hydrogenolysis activity of Ru and decrease the yield of low-molecular-weight gaseous products. Among these catalysts, Ru-Cu/HY showed the best HDO performance, affording the highest selectivity to hydrocarbon products. The improved catalytic performance of Ru-Cu/HY was probably a result of the following three factors: (1) high total and strong acid sites, (2) good dispersion of metal species and limited segregation, and (3) high adsorption capacity for polar fractions, including hydroxyl groups and ether bonds. Moreover, all bifunctional catalysts proved to be superior over the combination catalysts of Ru/Al O and HY zeolite.

Hydrodeoxygenation (HDO) of two dilute acid flowthrough pretreated softwood lignin samples, including residual lignin in pretreated solid residues (ReL) and recovered insoluble lignin in pretreated liquid (RISL), with apparent different physical and chemical structures, was comprehensively studied. A combination of catalysts (HY zeolite and Ru/Al2O3) was employed to investigate the effects of lignin structures, especially condensed structures, on the HDO upgrading process. Results indicated that the condensed structure and short side chains in lignin hindered its HDO conversion under different reaction conditions, including catalyst loading and composition, hydrogen pressure, and reaction time. In addition to lignin structure, HY zeolite was found crucial for lignin depolymerization, while Ru/Al2O3 and relatively high hydrogen pressure (4 MPa) were necessary for upgrading unstable oxy-compounds to cyclohexanes at high selectivity (>95 wt %). Since the lignin structure essentially affects its reactivity during HDO conversion, the yield and selectivity of HDO products can be predicted by detailed characterization of the lignin structure. The insights gained from this study in the fundamental reaction mechanisms based on the lignin structure will facilitate upgrading of lignin to high-value products for applications in the production of both fuels and chemicals.

A New Lignin BioJet: Jet fuel-range hydrocarbons (C7–C18) can be produced directly from biomass-derived lignin by selective C–O–C bond cleavage and simultaneous hydrodeoxygenation using combinations of noble metal catalysts (Ru/Al2O3) and acidic zeolites (H+-Y) in the aqueous phase.

Selective cleavage of C–O–C bonds in lignin without disrupting the C–C linkages can result in releasing aromatic monomers and dimers that can be subsequently converted into chemicals and fuels.

No abstract

No abstract

GRAPHICAL ABSTRACT | High catalytic efficiency of lignin depolymerization over low Pd-zeolite Y loading at mild temperature. This article reported a novel low-temperature process for aromatics production through lignin depolymerization catalyzed by 0.1 wt% Pd-zeolite Y catalyst prepared by a facile method. Under the same reactive condition, the as-prepared Pd-zeolite Y catalysts exhibited much higher catalytic efficiency than zeolite Y or commercial Pd/Al2O3-zeolite composites. The selectivity of the Pd-zeolite Y toward lignin depolymerization was also much higher than the other commercial zeolite-based catalysts. With the presence of hydrogen, aromatics were the predominant products with high yields of phenols and dimers (over 99%). The as-obtained aromatics can be promising feedstock for production of fuels or chemicals for various applications. Results revealed that the Pd-zeolite Y catalyst is a highly active catalyst for the cleavage of lignin interlinkages, especially the C-O-C bonds by hydrogenolysis.

Efficient cleavage of β-O-4 bonds in lignin to high-yield aromatic compounds for the potential production of fuels and chemicals is vital for the economics of the modern biorefinery industry. This work is distinct in that a detailed mechanistic analysis of the reaction pathways of veratrylglycero-β-guaiacyl ether (VGE) catalyzed by transition-metal-free solid acid zeolite in aqueous conditions at high hydrogen pressure has been performed. VGE degradation produced high monomers yields ( � 87 %), including guaiacol (48.2 %), 1-(3,4-dimethoxyphenyl)ethanol (10.3 %), 1-(3,4-dimethoxyphenyl)-2-propanol (6.1 %), 3,4-dimethoxyphenylpropanol (4.7 %), 3,4-dimeth-oxycinnamyl alcohol (4.1 %), and 1,2-dimethoxy-4propylbenzene (2 %). The products were identified and confirmed by the in situ solid-state magic angle spinning (MAS) 13 C NMR spectroscopy in real-time conditions and the twodimensional gas chromatography (GC × GC). A variety of products reveal the crucial role of hydrogen, water, and acid sites for heterolytic cleavage of the β-O-4 bond in VGE. Decarbonylation, hydrogenolysis, hydrogenation, and dehydration reaction pathways are proposed and further validated using first-principles calculations.