Layered double hydroxides supported atomically precise Aun nanoclusters for air oxidation of benzyl alcohol: Effects of size and active site structure

Abstract

The effects of size and active site structure on catalytic activity were deeply investigated in air oxidation of benzyl alcohol over a series of Ni3Al-LDH (layered double hydroxides)-supported Aun nanocluster (NC) catalysts Aun/LDH (n = 25, 38, ~127), obtained by modified electrostatic adsorption of atomically precise Au25Capt18, Au38Capt24 and Au~127-Capt (Capt: captopril) NCs followed proper calcination. Detailed characterizations show that the Au25/LDH, Au38/LDH and Au~127/LDH possess ultrafine Au NCs size of 1.2 ± 0.2, 1.4 ± 0.3 and 1.8 ± 0.5 nm, respectively, which are majorly dispersed on the edge sites of the small-sized LDH nanosheets (20–40 nm). All the catalysts exhibit excellent catalytic activities in air oxidation of benzyl alcohol without external base associated with the remarkable size- and active site structure-dependence. The catalyst Au38/LDH shows the highest activity with TOF of 1884 h−1, which can be attributable to the ultrafine bi-icosahedron structure Au38 NCs and the strongest Au38 NCs – Ni-OH (LDH) synergistic effect facilitating the activation of α-CH bond of benzyl alcohol over more negatively charged Au sites upon XPS, CO-DRIFTs and kinetic isotope studies. The findings of the size- and active site structure-dependence of supported Aun cluster catalysts in the oxidation of benzyl alcohol provide important guiding principles for the rational design of supported Aun cluster catalysts.