The reductive catalytic fractionation (RCF) of lignocellulosic and herbaceous biomass over heterogeneous catalysts has been demonstrated to recover high-yield phenolic monomers and holocellulose-rich solids effectively, and these products could be further used to produce value-added chemicals and second-generation biofuel. Catalyst selection plays a critical role in the performance of the RCF process, and noble metal catalysts (e.g., Pt, Pd, and Ru) with a high loading of 5 wt % have been extensively used to obtain high-yield phenolic monomers and delignified holocellulose-rich solids. In this study, we demonstrated that the RCF of biomass over extremely low Pd loaded on N-doped carbon (CN x ) support catalysts could produce phenolic monomers at approximately theoretical maximum yield and presented high holocellulose-rich solid recovery. When birch wood was converted over the catalyst with 0.25 wt % Pd loaded on CN x (Pd0.25/CN x ) at 250 °C and an initial H2 pressure of 3.0 MPa for 3 h, a lignin-derived phenolic monomer carbon yield and highly delignified holocellulose recovery of 52.7 C % and 84.2 wt %, respectively, were achieved. The Pd0.25/CN x catalyst contained both ultrasmall Pd nanoclusters and single Pd atoms, which were stabilized on the N-functionalized carbon support. The highly activated hydrogenolysis and double-bond saturation that occurred over the Pd0.25/CN x catalyst dominantly produced 4-n-propyl guaiacol/syringol. In contrast, 4-n-propanol guaiacol/syringol with residual −OH groups was the major species obtained over the typical 5 wt % Pd/activated carbon catalyst. The plausible reaction pathways for the production of different types of phenolic monomers were discussed using density functional theory calculations. The excellent RCF performance of the Pd0.25/CN x catalyst was demonstrated using other types of biomass, such as oak, pine, and miscanthus. The successful use of extremely low-Pd-loaded catalysts is advantageous for implementing economically viable RCF techniques.
Catalytic conversion of technical lignin to value-added chemicals and fuels is important for realizing economically viable lignocellulosic biomass refineries. The choice of catalysts and solvents is critical for the effective conversion of the technical lignin to chemicals and fuels by the cleavage of the C−C bonds. In this study, catalytic depolymerization and hydrodeoxygenation of Kraft lignin (KL) were investigated over bimetallic ZnO and Co deposited on N-doped carbon nanotubes (ZnO-Co/N-CNTs) in an aqueous medium. The catalytic activity of ZnO-Co/N-CNTs was compared with those of various noble and non-noble metal-based catalysts. Almost complete KL conversion with a very low solid residue yield (5 wt %), a high bio-oil yield (52 wt %), a high degree of deoxygenation (DOD, 59.0%), and a high monomeric yield (12.1 wt %) was achieved over ZnO-Co/N-CNTs at 350 °C and 6 h reaction time. The monomers mainly consisted of cyclohexanone and its alkyl-substituted derivatives and alkylated phenols. At 400 °C, the monomeric yield and DOD increased to 24.4 wt %and 61.0%, respectively. In addition, the produced bio-oil exhibited high-calorific values of 34.3−37.0 MJ kg −1 because of the high activity of ZnO-Co/N-CNTs for hydrodeoxygenation. ZnO-Co/N-CNTs outperformed most of the metalsupported catalysts including 5 wt % Pd, 5 wt % Ru, 5 wt % Pt, 66 wt % Ni, and CoMo on various supports of activated carbon and alumina. The use of water as the solvent resulted in much higher bio-oil and monomeric yields than those using methanol, isopropyl alcohol, and n-hexane (12−37 and 3.2−4.1 wt %, respectively). The high bio-oil and monomeric yields with a high DOD in water make ZnO-Co/N-CNTs highly attractive in the development of an environmentally friendly technical lignin conversion process.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.