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 pro- cesses.Herein, atom probe tomography (APT) has been used to spatially resolve the 3D compositional changes at the sub- nm length scale in asingle zeolite ZSM-5 crystal, whichhas been partially deactivated by the methanol-to-hydrocarbons reaction using 13 C-labeled methanol. The results reveal the formation of coke in agglomerates that span length scales from tens of nanometers to atomic clusters withamedian size of 30– 60 13 Catoms.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 engineer- ing materials to suppress detrimental coke formation.