Bimetallic AuPd Nanocluster Catalysts with Controlled Atomic Gold Distribution for Oxidative Dehydrogenation of Tetralin

A simple and versatile method for the preparation of bimetallic AuPd nanoclusters (NCs) with controlled atomic gold distributions and stabilization by poly(vinyl-2-pyrrolidone) is demonstrated. The dropwise injection of ethanolic HAuCl4 and the strong acidic reaction environment assist the control of the distribution of gold atoms on preformed Pd NCs. These bimetallic NCs are highly active and selective catalysts for the dehydrogenative aromatization of tetralin into naphthalene. Several AuPd NC catalysts have been tested, and these results demonstrate that AuPd NCs with the lowest gold content have higher catalytic activity. Characterization, including extended X-ray absorption fine structure and X-ray absorption near-edge structure analyses, reveals that AuPd NCs with the lowest gold content have more Au-Pd heterobonds, which play a key role in the dehydrogenative aromatization reaction. In contrast, transmission electron microscopy and high-resolution TEM analyses show that AuPd NCs with a greater gold content have island-like morphologies, where nanocrystalline gold is deposited on the surfaces of the Pd NCs, which reduces the number of Au-Pd bond active sites on the Pd NC surfaces. Our study reveals that tuning of the Au-Pd bond on the surface of the Pd NCs with a very low content of gold results in high synergy in catalytic activity and may be expected to be applicable to a wide variety of bimetallic NCs.