Utilizing operando catalyst regeneration to uncover insights in the methanol-to-hydrocarbons process

The methanol-to-hydrocarbons (MTH) catalyst deactivation is reversible, and deactivating coke molecules can be removed via regeneration experiments. Regeneration of small-pore zeolite SSZ-13 first leads to the elimination of polyaromatic deactivating compounds, leaving the active aromatic intermediates intact. Partial regeneration experiments can provide an alternative approach to study small-pore zeolites by mimicking co-feeding of aromatic intermediates. Catalyst properties and reaction intermediates were followed with operando UV-visible spectroscopy and X-ray diffraction. It was shown that all the coke is formed within the zeolite cages and that the lattice expansion is due to the formation of hydrocarbon molecules. Additionally, indications for separate reaction mechanisms to produce ethylene and propylene were established. With confocal fluorescence microscopy (CFM), it was determined that upon regeneration, the hydrocarbons were less conjugated and more homogeneously distributed. A full hydrocarbon pool mechanism was established for the MTH reaction over zeolite SSZ-13.