Quantifying a Heterogeneous Ru Catalyst on Carbon Black Using ADF STEM

Abstract

Ru catalysts are part of a set of late transition metal nanocatalysts that have garnered much interest for catalytic applications such as ammonia synthesis and fuel cell production. Their performance varies greatly depending on their morphology and size, these catalysts are widely studied using electron microscopy. Using recent developments in annular dark field (ADF) scanning transmission electron microscopy (STEM) quantification techniques, a rapid atom counting procedure is utilized to document the evolution of a heterogeneous Ru catalyst supported on carbon black. Areas of the catalyst are imaged for ≈15 min using ADF STEM. When the Ru clusters are exposed to the electron beam, the clusters change phase from amorphous to crystalline. To quantify the thickness of the crystalline clusters, two techniques are applied (simulation and statistical decomposition) and compared. These techniques show that stable face centered cubic crystal structures in the form of rafts, between 2 and 8 atoms thick, are formed after the initial wetting of the carbon support.