Maximizing Hydrogen Efficiency in the Conversion of Biorenewables to Polymer Precursors

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Illustration of catalytic hydrodemethoxylation
The catalytic hydrodemethoxylation of guaiacol and related compounds is achieved under mild conditions using Pd supported on high surface ceria. The reaction takes place with almost quantitative hydrogen mass balance.

The conversion of guaiacol into the nylon precursors, cyclohexanol and cyclohexanone, is catalyzed by palladium supported on high surface area ceria (Pd/HS CeO2) under mild conditions (100 °C, ≤1 bar H2) via sequential hydrodemethoxylation and hydrogenation.

In contrast, the 2-methoxycyclohexanol side product is generated by direct guaiacol hydrogenation.

Reaction selectivity is determined by competing C-O bond hydrogenolysis versus arene hydrogenation.

Hydrogenolysis selectivity increases as H2 pressure decreases, and over 80 % H2 is incorporated into the products at 1 bar H2.

Higher reactivity of guaiacol than anisole implies that the hydroxyl group is essential in Pd/HS CeO2 catalysis.

The combination of near quantitative mass balance of H2, high recyclability, and use of water as a solvent offers a simple, green and efficient conversion of lignin-derived aromatics into commercial products.

Zhou, H., Wang, H., Sadow, A.D., Slowing, I.I. “Toward hydrogen economy: Selective guaiacol hydrogenolysis under ambient hydrogen pressure.” Appl. Catal. B: Environ. 2020, 270, 118890.