Mechanistic Study of Pt–Re/γ-Al₂O₃ Catalyst Deactivation by Chemical Imaging of Carbonaceous Deposits Using Advanced X‑ray Detection in Scanning Transmission Electron Microscopy

Accumulation of carbonaceous deposits (also known industrially as “coke”) on catalytic active sites derived from process conditions has been a long-standing problem in industrial catalysis. Over accumulation of the deposits ultimately lead to deactivation; thus, characterization of coke evolution becomes critical toward developing catalytic materials with improved stability. This study focuses on extending an understanding of how and where coke forms on Pt–Re/γ-Al₂O₃, an industrial catalyst used in reforming processes. With the use of spherical aberration-corrected scanning transmission electron microscopy (C_s-STEM) and enhanced energy dispersive X-ray spectroscopy (EDX), we characterize the Pt–Re metal sites and show, to our knowledge, the first examples of chemically imaged subnanometer particles and also the first to use chemical maps to identify coke location on a catalyst. A two-step mechanism is reported based on the results whereby coke appears to stream from the metal function of the catalyst resulting in heterogeneous coverage