The industrial production of monophenols was mainly dependent on fossil resources, due to growing energy demand and escalating environmental issues, more efficient and sustainable strategy, such as utilization of biomass as raw materials to economically produce monophenols, was desired, which could liberate us from the reliance on fossil resource and was of great industrial and social significance. Herein, a novel strategy was reported to produce biomass-derived monophenols from lignin by directly deconstructing C-O bond under mild conditions. A series of NiM-MOFs (M=Co, Mo, and Cu) derived bimetallic catalysts were synthesized via a simple hydrothermal method, which were characterized by XRD , SEM , TEM , XPS and NH 3 -TPD. The synergistic effect between the Ni and Mo greatly improved the catalytic activity and inhibited the transformation to by-products. In addition, we explored a new binary solvents system of MeOH-THF to effectively enhance the selectivity of monophenols. Under optimal catalytic conditions, Ni4Mo1/C-BN catalyst could break the C-O bonds in lignin dimer under 160 ℃ to afford phenol and benzoic acid , and the possible reaction pathway was proposed. The high yield of lignin oil from the oxidation of various realistic lignin also confirmed the superiority of this catalytic system. The lignin depolymerization products were characterized by element analysis, GPC and GC-MS, confirming the presence of mainly guaiacyl-type (G) products, while the highest yield was assigned to vanillin.
By encapsulating metal nanoparticles (NPs), the synergistic effect between the metalloporphyrins and the metal nanoparticles in metalloporphyrin organic frameworks (P-MOFs) can boost its catalytic performance. The self-coupling reaction of terminal alkynes is a kind of important organic reaction and can take place with the aid of the catalyst. A nanorod-like metal-organic skeleton PCN-222(Cu) with carboxy porphyrins as ligands was synthesized as the precursor. By a double-solvent approach, the composite catalysts with varying copper nano-loadings in PCN-222(Cu) pores were obtained. Among them, 1.9 wt% of Cu NPs in Cu@PCN-222(Cu) has excellent catalytic activity and stability for the self-coupling reaction of terminal alkynes. PCN-222(Cu) can stabilize the Cu NPs, control the size selectivity and crystal form. The copper porphyrins and Cu NPs in Cu@PCN-222(Cu) both serve as the catalytic active sites. This strategy, which using porphyrin-structured MOFs to construct dual active sites with the same element, has promising applications in MOFs catalysis.
Ni-based MOFs catalysts are promising candidates that can be used to achieve biomass valorization following the process of selective hydrogenolysis process. Here we report a spherical NiCo-based MOFs catalyst, which provides a larger BET surface to enhance 2-phenoxy-1-phenylethan-1-ol molecules enrichment and promote the hydrogenolysis on spherical NiCo-based MOFs catalyst surface. In addition, the synergistic interaction between Ni and Co species also shows great effect on catalytic hydrogenolysis of 2-phenoxy-1-phenylethan-1-ol molecules and enzymatic lignin. The yields of ethylcyclohexane and cyclohexanol are dramatically improved to more than 90 mol% over Ni3Co1-based MOFs catalyst under nitrogen atmosphere. Various lignin dimers derivatives are investigated over Ni3Co1-based MOFs catalyst, which indicates oxygen-containing functional groups played a critical role in the hydrogenolysis process. Isopropanol is used as solvent in the hydrogenolysis of 2-phenoxy-1-phenylethan-1-ol molecules and enzymatic lignin. 21% of H 2 is observed in the GC/MS, suggesting that it is a catalytic transfer hydrogenolysis process. Catalytic hydrogenolysis of enzymatic lignin is also carried out under 280 ℃ over optimal Ni3Co1-based MOFs catalyst for 6 h, giving highest lignin oil yield (75.6 wt%) and lower O/C ratio (0.17). This work can be extended to different biomass valorizations to promote the catalytic behavior of spherical MOFs catalysts.
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