科研之友
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摘要
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/gamma-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.
