Beyond flower-like structure – The synergy within Pd/Ni-Al hydrotalcite for base-free oxidation of benzyl alcohols

Abstract

A highly efficient supported metal catalyst, Pd/Ni-Al hydrotalcite with flower-like structure was synthesized and applied for catalytic oxidation of benzyl alcohols; affording >99 % conversion and 94–100 % selectivity in a base-free solution. The surface basicity and cation-oxygen mode in the layer of hydrotalcite were found to be pronouncedly associated with the changes of morphologies of the Ni-Al hydrotalcites. Compared to negligible activity by Ni-Al hydrotalcite itself, low efficiency by Pd nanoparticles or its simple mixture with Ni-Al hydrotalcite, a significant enhancement in the catalytic activity by the Pd deposited on flower-like Ni-Al hydrotalcites suggested a synergistic effect occurred between Pd and well-structured Ni-Al hydrotalcite. A plausible mechanism for the catalytic reaction involving the formation of metal-alkoxide and metal-hydroperoxide intermediates was postulated based on the control reactions, FTIR and XPS analysis and Hammett experiment.