Coke Formation in a Zeolite Crystal During the Methanol-to-Hydrocarbons Reaction as Studied with Atom Probe Tomography

Understanding the formation of carbon deposits in zeolites is vital to developing new, superior materials for various applications, including oil and gas conversion processes. Herein, atom probe tomography (APT) has been used to spatially resolve the 3D compositional changes at the sub‐nm length scale in a single zeolite ZSM‐5 crystal, which has been partially deactivated by the methanol‐to‐hydrocarbons reaction using 13C‐labeled methanol. The results reveal the formation of coke in agglomerates that span length scales from tens of nanometers to atomic clusters with a median size of 30–60 13C atoms. These clusters correlate with local increases in Brønsted acid site density, demonstrating that the formation of the first deactivating coke precursor molecules occurs in nanoscopic regions enriched in aluminum. This nanoscale correlation underscores the importance of carefully engineering materials to suppress detrimental coke formation. Al have a coke: Atom probe tomography (APT) has been used for the first time to probe the nanoscale distribution of coke deposits within a single zeolite ZSM‐5 crystal used in the methanol‐to‐hydrocarbons reaction. Cluster analysis of the 13C, Al, and Si APT data has identified isolated clusters of approximately 30–60 13C atoms that are intimately correlated with sub‐nm increases in Brønsted acid site density. Possible coke species present in the 13C clusters are shown.