Atomically Dispersed Precious Metal Species on Various Oxide Supports for Catalytic Hydrogen Upgrading and Emission Control

Sir Hugh Stott Taylor first defined the concept of “catalytic active sites” in 1925 as the place where the catalytic reaction occurs. In a homogeneous phase, the active sites are uniquely defined, but on a heterogeneous catalyst surface, it is always challenging to identify the active sites; the latter often change with the operating conditions and are disguised by the presence of nanoparticles (NPs), which typically contain many metal atoms that do not catalyze the reactions [1]. Prior work at Tufts has established that sub-nm Au and Pt species (undetectable by regular TEM) catalyze the low-temperature water-gas shift (WGS) reaction [2, 3]. The concept of single-site heterogeneous catalysts may bring together homogeneous and heterogeneous catalysis. In the heterogeneous catalysts systems, how to best identify the exact active sites at the atomic scale, and to maximize the exact structures so that they remain stable under the reaction conditions is challenging. In the present work, it is shown that atomically dispersed single-site Pt and Au species can be prepared on various support oxides to meet diverse fuel gas processing reaction scenarios (Figure 1). Aberration-corrected high-angle annular darkfield STEM imaging is particularly useful for characterizing single-atom catalyst dispersions.