Boehmite lattice hydroxyl-mediated selective hydrogenation of cinnamaldehyde via water as hydrogen source

Abstract

Selective hydrogenation of cinnamaldehyde (CAL) to cinnamyl alcohol (COL) using water as the hydrogen source offers a promising route to eliminate traditional H₂ preparation. However, this approach faces a trade-off between concurrently crating abundant active hydroxyls for hydrogenation and readily removing residual oxygen under mild conditions, restricting current development. Here, we report a naturally abundant lattice hydroxyl-mediated selective hydrogenation process over a boehmite-supported gold catalyst (Au/AlOOH), using H₂O as the hydrogen source and CO as the oxygen acceptor. This process achieves 79% CAL conversion and 84% COL selectivity at 90 °C, doubling the efficiency of H₂-based hydrogenation counterpart. In contrast, the OH-free Au/Al₂O₃ shows no activity. Mechanistic studies indicate that the Au/AlOOH boundary provides unsaturated Al³⁺ sites for selective C=O adsorption and lattice hydroxyls for hydrogenation, which are continuously replenished from water. CO adsorbed on Au facilitates oxygen removal, regenerating Al³⁺ sites. This work presents a practical hydrogen transfer strategy that leverages the unique lattice hydroxyls of boehmite to efficiently extract hydrogen from water.