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Sodium lignosulfonate (LS) was valorized to low molecular weight (Mw) fractions by combining solvothermal (SF) and catalytic hydrogenolysis/hydrogenation fragmentation (SHF) in a continuous flow system. This was achieved in either alcohol/H2O (EtOH/H2O or MeOH/H2O) or H2O as a solvent and Ni on nitrogen-doped carbon as a catalyst. The tunability according to the temperature of both SF and catalytic SHF of LS has been separately investigated at 150 °C, 200 °C, and 250 °C. In SF, the minimal Mw was 2994 g mol−1 at 250 °C with a dispersity (Đ) of 5.3 using MeOH/H2O. In catalytic SHF using MeOH/H2O, extremely low Mw was found (433 mg gLS−1) with a Đ of 1.2 combined with 34 mg gLS−1. The monomer yield was improved to 42 mg gLS−1 using dual catalytic beds. These results provide direct evidence that lignin is an unstable polymer at elevated temperatures and could be efficiently deconstructed under hydrothermal conditions with and without a catalyst. [ABSTRACT FROM AUTHOR]

Hydrogenation reactions in water at elevated temperatures are challenging for heterogeneous catalysts. Thus, we present a simple, cheap, scalable, and sustainable approach for synthesizing an efficient and stable Ni catalyst supported on highly porous nitrogen-doped carbon (NDC) in pellet form. The performance of this catalyst was evaluated in the aqueous-phase hydrogenation of lignocellulosic biomass-derived compounds, i.e., glucose (Glu), xylose (Xyl), and vanillin (V), using a continuous-flow system. The as-prepared 35 wt% Ni on NDC catalyst exhibited a high catalytic performance in all three aqueous-phase hydrogenation reactions, i.e., the conversion of Glu, Xyl, and V was 96.3 mol%, 85 mol%, and 100 mol% and the yield of sorbitol (Sor), xylitol (Xyt), and 2-methoxy-4-methylphenol (MMP) was 82 mol%, 62 mol%, and 100 mol%, respectively. This high activity was attributed to the high specific surface area of NDC and mainly to the heterojunction effects stabilizing and adjusting the homogenously and highly dispersed Ni nanoparticles (ANi = 20 m2 g−1) on the surface of NDC. Changing the electron density in the nickel nanoparticles allows the high performance of the catalyst for a long time on stream (40 h) with minimized Ni leaching and without the loss in catalytic performance. [ABSTRACT FROM AUTHOR]