Nature of active sites and deactivation mechanism for n-butane isomerization over alumina-promoted sulfated zirconia

• Two active sites, reducible sites and acid sites, exist on the catalyst surface.
• Reducible sites and acid sites show synergistic effects in n-butane isomerization.
• Equilibrium is reached between butane + sulfate species and butene + sulfite species.
• Deactivation is mainly caused by the consumption of reducible active sites.
• A new proposed reaction model can predict the isomerization activity well.

The deactivation of n-butane isomerization on alumina-promoted sulfated zirconia (SZA) was studied at 473 K under atmospheric pressure. Under N2, the regeneration temperature influences the isomerization activity greatly. The change of the sulfate species during the deactivation process was determined quantitatively by a temperature-programmed evolution mass spectrometer. Two active sites, reducible sites and acid sites, exist on the catalyst surface and show a synergistic effect on the n-butane isomerization reaction. The reducible sulfate species play an important role in butene formation via oxidative dehydrogenation of n-butane, while the acid sites are responsible for the isomerization steps. The reduction of sulfate species and the accumulation of sulfite species on the surface, which cause the decrease of butene concentration in the catalyst bed, are the main reasons for catalyst deactivation. Based on these findings, a new reaction model and two possible ways to improve the catalytic stability of SZA catalyst are proposed.

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