Gold single-atom catalysts (SACs) exhibit outstanding reactivity in various reactions, including the hydrochlorination of acetylene to vinyl chloride, but their practical applicability is compromised by (i) current synthesis protocols, using aqua regia as chlorine‑based dispersing agent, and (ii) their high susceptibility to sintering on non‑functionalized carbon supports at > 500 K and/or under reaction conditions. In this study led by the group of Prof. Pérez-Ramírez at ETH Zurich, a sustainable and potentially scalable route for the synthesis of carbon-supported gold nanostructures in bimetallic catalysts was developed by employing a range of transition metal salts as alternative chlorine source, allowing for tailored gold dispersion, ultimately reaching atomic level when using H2PtCl6. By combining kinetic analysis, scanning transmission electron microscopy, and X-ray adsorption analysis at the SuperXAS beamline of the SLS, the degree of gold dispersion and the coordination environment (i.e., Cl-ligands, C/O-defects on the carbon) of the metal sites was assessed as a function of several synthesis parameters (i.e., pH, Cl-content) as well as the choice of metal chlorides. The results indicate the key role of platinum in promoting a chloride-mediated dispersion mechanism, which can be further used to redisperse large gold nanoparticles (>70 nm) on carbon carriers into isolated atoms, having important implications for catalyst regeneration. Another key role of platinum single atoms is to effectively inhibit the agglomeration of their gold-based analogs up to 800 K and during acetylene hydrochlorination, despite their spatial isolation and thus without compromising the high activity of Au(I)-Cl active sites. Accordingly, exploiting cooperativity effects of a second metal is a promising strategy towards practical applicability of gold SACs, opening up exciting opportunities at the frontier of multifunctional single-atom catalysis.
Contact
Dr Adam H. Clark
SuperXAS beamline
Operando spectroscopy group & Laboratory for Synchrotron Radiation and Femtochemistry (LSF)
Swiss Light Source, Paul Scherrer Intitute
5232 Villigen-PSI, Switzerland
Telephone: +41 56 310 58 05
E-mail: adam.clark@psi.ch
Original Publication
Selina K Kaiser, Adam H Clark, Lucrezia Cartocci, Frank Krumeich, Javier Pérez-Ramírez
Small, 12 January 2021
DOI:10.1002/smll.202004599