Supercritical fluid removal of hydrocarbons adsorbed on wide-pore zeolite catalysts

The effect of zeolite pore structure on coke removal by supercritical fluid regeneration (SFR) was studied on a series of wide-pore zeolites, including acidic Y, beta, and mordenite zeolites. Catalyst samples were deactivated under isobutane/butene reaction conditions and treated under flowing supercritical isobutane for 60 min. The chemical nature of the species remaining on the catalyst surface was analyzed by temperature-programmed oxidation, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and ultraviolet–visible spectroscopy. Even though most adsorbed hydrocarbons were removed in some catalysts, DRIFTS spectra indicated that none of the catalysts was completely free of hydrocarbon deposits after SFR. Cyclic reaction/SFR experiments on USY and beta zeolites showed that neither catalyst recovered its initial performance, and also demonstrated a continuous decrease in activity. However, the decrease of activity between cycles was slower in the beta sample, probably due to hindered formation of unsaturated cyclic or polycyclic compounds.