Abstract: Pd catalysts supported on various supports have been studied for the oxidant-free dehydrogenation of alcohols. The Pd catalyst loaded on hydrotalcite (HT), which is an acid-base bifunctional support, demonstrates superior benzyl alcohol conversion and benzaldehyde selectivity. Detailed studies using the Pd/HT catalyst reveal that the best performance can be obtained over the catalyst with w(Pd) = 0.32%–0.55%. The Pd/HT can be used repeatedly without significant deactivation and can efficiently catalyze the dehydrogenation of various alcohols including the substituted benzylic alcohols, 2-thiophenemethanol, α,β-unsaturated alcohols, and cyclic aliphatic alcohols. The characterization results show that the Pd(II) species over the HT are transformed into Pd nanoparticles or nanoclusters with mean size of 2.0–2.5 nm during the reaction. The highly dispersed Pd(II) species in the catalyst precursors can lead to the formation of smaller Pd nanoparticles, favoring the catalytic performance. We speculate that the basicity of the catalyst may promote the activation of the O-H bond of alcohol to form a Pd-benzyl alcoholate intermediate, which undergoes β-H abstraction by Pd nanoparticles, and the Brönsted acid sites on the catalyst surface may facilitate the release of H2 by the interaction with the formed hydride species on Pd nanoparticles.

Key words: green catalysis, alcohol, dehydrogenation, hydrotalcite, palladium, nanoparticle, acid-base bifunctionality