Photocatalytic Cleavage of β-O-4 Ether Bonds in Lignin over Ni/TiO2

Abstract

It is of great importance to explore the selective hydrogenolysis of β-O-4 linkages, which account for 45–60% of all linkages in native lignin, to produce valued-added chemicals and fuels from biomass employing UV light as catalyst. TiO2 exhibited satisfactory catalytic performances in various photochemical reactions, due to its versatile advantages involving high catalytic activity, low cost and non-toxicity. In this work, 20 wt.% Ni/TiO2 and oxidant PCC (Pyridinium chlorochromate) were employed to promote the cleavage of β-O-4 alcohol to obtain high value chemicals under UV irradiation at room temperature. The Ni/TiO2 photocatalyst can be magnetically recovered and efficiently reused in the following four consecutive recycling tests in the cleavage of β-O-4 ether bond in lignin. Mechanism studies suggested that the oxidation of β-O-4 alcohol to β-O-4 ketone by oxidant PCC first occurred during the reaction, and was followed by the photocatalysis of the obtained β-O-4 ketone to corresponding acetophenone and phenol derivates. Furthermore, the system was tested on a variety of lignin model substrates containing β-O-4 linkage for the generation of fragmentation products in good to excellent results.

Photophysics of Perylene Diimide Dianions and Their Application in Photoredox Catalysis

“…Chemie strates 4-8 was previously explored with different photocatalysts, [40] among them at ype of heteroleptic cyclometalated iridium(III) complex for which subsequent mechanistic studies demonstrated that in the presence of large excess of tertiary amine as sacrificial electron donor, the initial iridium-(III) complex is first converted to another iridium(III) compound, [40b] which is then the actual catalytically active species. [8,42] Here,i nt he case of the PDI dianions,t he lignin model substrate photocleavage seems to occur via am ore straightforward mechanism.…”

Catalytic Conversion of Lignin to Liquid Fuels with an Improved H/Ceff Value over Bimetallic NiMo-MOF-Derived Catalysts

“…Thus, moderate amounts of methoxy-substituted aromatic rings were detected, which was consistent with the results in Table . β-O-4 model compounds with γ-OH could represent the lignin typical realistic segment . Therefore, 2-(2-methoxyphenoxy)-1-(4-methoxyphenyl)­propane-1,3-diol was selected as a model compound and tp afford 42, 40, and 8% yields of 1-methoxy-4-propylcyclohexane, 2-methoxycyclohexan-1-ol, and cyclohexanol, respectively (Table entry 6).…”

Photophysics of Perylene Diimide Dianions and Their Application in Photoredox Catalysis

“…[39] To test this concept, we investigated the visible-light-mediated C a À Ob ond cleavage in small molecules resembling the lignin biopolymer (Table 3). This reaction requires fairly negative reduction potentials, [40] and it is of interest from an application-oriented perspective in which the controlled depolymerization of lignin would lead to useful commodity products. [40b,41] Substrates 4-8 (Table 3) were dissolved along with 1mol %o fP DI(H)-dipp in acetonitrile,a nd then am ixture of Na 2 S 2 O 4 (3 equivalents) and tetra-n-butylammonium chloride (TBACl, 0.2 equivalents) in water was added under oxygen-free conditions (SI page S38).…”

“…Forschungsartikel strates 4-8 was previously explored with different photocatalysts, [40] among them at ype of heteroleptic cyclometalated iridium(III) complex for which subsequent mechanistic studies demonstrated that in the presence of large excess of tertiary amine as sacrificial electron donor, the initial iridium-(III) complex is first converted to another iridium(III) compound, [40b] which is then the actual catalytically active species. [8,42] Here,i nt he case of the PDI dianions,t he lignin model substrate photocleavage seems to occur via am ore straightforward mechanism.…”