Pursuing unprecedented anisotropic morphologies of halide-free Pd nanoparticles by tuning their nucleation and growth

Abstract

In this paper, a highly effective and scalable polyol-based modified procedure is reported, yielding shape-controlled Pd nanoparticles (NPs) formed via two distinct growth mechanisms as a function of apparent pH. Starting from tetraethylammonium tetrahydroxypalladate (TEA)₂[Pd(OH)₄], a halide-free precursor, the resulting shape of the NPs ranged from highly defective worm-like nanostructures to well-defined polyhedra (tetrahedra, octahedra and 5-fold twins) as shown by TEM, HRTEM, and STEM. The effect of the different synthesis parameters was thoroughly investigated, finding that apparent pH – modulated by adding diluted HNO₃ – is the key parameter in determining the final size and shape of Pd NPs, whose evolution was followed during the reaction. A rational explanation of the observed shape modification as a function of apparent pH was proposed. The as-prepared Pd NPs, once dried, were analysed by means of XRD. DRIFT spectroscopy was used to show how CO binds on the Pd NPs after deposition on γ-Al₂O₃ as catalytic support.