Elucidating the Reaction Pathways of Veratrylglycero‐β‐Guaiacyl Ether Degradation over Metal‐Free Solid Acid Catalyst with Hydrogen

• Published in: ChemSusChem 2023-03, Vol.16 (6), p.e202202001-n/a
• Main Authors: Ruan, Hao, Xu, Zhangyang, Kumar, Adarsh, Feng, Maoqi, Lipton, Andrew S., Walter, Eric D., Gieleciak, Rafal, Paudel, Hari P., Duan, Yuhua, Yang, Bin
• Format: Article
• Language: English
• Subjects: acid catalysis; Aromatic compounds; Chemical bonds; Cleavage; Degradation; Dehydration; Ethanol; Gas chromatography; Hydrogenolysis; in situ solid-state NMR; lignin degradation; NMR spectroscopy; phenolic monomers; Propylbenzene; β-O-4 cleavage mechanism
• ISSN: 1864-5631; 1864-564X
• DOI: 10.1002/cssc.202202001

Efficient cleavage of β‐O‐4 bonds in lignin to high‐yield aromatic compounds for the potential production of fuels and chemicals is vital for the economics of the modern biorefinery industry. This work is distinct in that a detailed mechanistic analysis of the reaction pathways of veratrylglycero‐β‐guaiacyl ether (VGE) catalyzed by transition‐metal‐free solid acid zeolite in aqueous conditions at high hydrogen pressure has been performed. VGE degradation produced high monomers yields (≈87 %), including guaiacol (48.2 %), 1‐(3,4‐dimethoxyphenyl)ethanol (10.3 %), 1‐(3,4‐dimethoxyphenyl)‐2‐propanol (6.1 %), 3,4‐dimethoxyphenylpropanol (4.7 %), 3,4‐dimethoxycinnamyl alcohol (4.1 %), and 1,2‐dimethoxy‐4‐propylbenzene (2 %). The products were identified and confirmed by the in situ solid‐state magic angle spinning (MAS) 13C NMR spectroscopy in real‐time conditions and the two‐dimensional gas chromatography (GC×GC). A variety of products reveal the crucial role of hydrogen, water, and acid sites for heterolytic cleavage of the β‐O‐4 bond in VGE. Decarbonylation, hydrogenolysis, hydrogenation, and dehydration reaction pathways are proposed and further validated using first‐principles calculations. Cleave the bond: Zeolite depolymerized β‐guaiacyl ether to produce monomers (≈87 %). Identification of various products reveals the crucial role of hydrogen, water, and acid sites in the heterolytic cleavage of the β‐O‐4 bond. Mechanistic analysis reveals that dehydration, decarbonylation, and hydrogenolysis were the main reactions taking place along with demethylation and hydrogenation.