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.