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

• Main Authors: Changzhou Chen, Peng Liu, Haihong Xia, Minghao Zhou, Jiaping Zhao, Brajendra K. Sharma, Jianchun Jiang
• Format: Article
• Language: English
• Published: MDPI AG 2020-04-01
• Series: Molecules
• Subjects: lignin; β-<i>O</i>-4; photocatalyst; Ni/TiO₂; oxidant PCC
• Online Access: https://www.mdpi.com/1420-3049/25/9/2109

It is of great importance to explore the selective hydrogenolysis of β-<i>O</i>-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-<i>O</i>-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-<i>O</i>-4 ether bond in lignin. Mechanism studies suggested that the oxidation of β-<i>O</i>-4 alcohol to β-<i>O</i>-4 ketone by oxidant PCC first occurred during the reaction, and was followed by the photocatalysis of the obtained β-<i>O</i>-4 ketone to corresponding acetophenone and phenol derivates. Furthermore, the system was tested on a variety of lignin model substrates containing β-<i>O</i>-4 linkage for the generation of fragmentation products in good to excellent results.