Butane isomerization on several H-zeolite catalysts.

H-ZSM-5, H-Beta, H-Mordenite and H-Y zeolites are active catalysts for n- butane isomerization. The level of activity and resistance to poisoning are a function of the concentration of the Bronsted acid sites and framework structure. H-L and H-Ferrierite zeolites have a very low activity. Silicalite-l (S-1) and mesoporous silica-alumina (MSA) are not active. The isobutane yield on ultrastable H-Y (Si/Al=3.15) catalyst is lower in comparison to tungsta supported on zirconia (WOx/ZrO2), H- Mordenite, H-Beta and H-ZSM-5 catalysts, however, H-Y catalysts are more resistent to poisoning and highly selective towards isobutane. In fact, no deactivation of H-Y catalysts was observed after 5 h of time on stream. On the contrary, WOx/ZrO2, H-Mordenite and H-Beta catalysts, under the same experimental conditions, are deactivated in less than 1 h of time on stream. It is suggested that the stability of the H-Y catalysts in comparison to the other acidic zeolites catalysts may be due to the 3-dimensional structure of H-Y zeolites, made of large supercages interconnected by apertures of 12 oxygen atoms. H-ZSM-5 catalysts are stable with time on stream but their selectivity to isobutane is very low. Active acidic molecular sieves with monodimensional structure (H- Mordenite, H-Beta) may favor the formation of polyenyl unsaturated chains, the precursors of the coke responsible for the catalysts deactivation.