Hydroisomerization of n-octane over platinum catalysts with or without binder

Abstract

The catalytic performance for the hydroisomerization of n-octane (conversion, selectivity and yield) of sets of bifunctional catalysts based on mordenite, beta and ZSM-5 zeolites with or without a binder (bentonite) were compared. As hydrogenating–dehydrogenating function, platinum supported by impregnation (1 wt.%) was used. It was found that the activity decreased in the following order: ZSM-5 > beta > mordenite-based catalysts. A decrease in the activity of agglomerated samples, because of the neutralization of the acid sites by the binder, was expected. The activity decrease was significantly high for ZSM-5 zeolite but the opposite effect was observed for beta zeolite. The presence of aluminium extraframework (EFAL) species in the beta agglomerated sample should be the responsible of this behaviour because of a synergetic effect between these EFAL species and the structural Brönsted acid sites causing an increase of the acid strength. The octane isomers selectivity for the agglomerated mordenite and beta samples was very similar to that in the non-agglomerated ones. ZSM-5 agglomerated sample yielded higher isomer selectivity than the non-agglomerated one. The higher neutralization of the acid sites by the binder was the responsible to that because leads to a higher concentration of carbenium ions, which provide the octane isomers. Also, the binder provided meso and macropores to the zeolite where the metal was likely located avoiding a possible pore partial blockage, with the consequently lower diffusional constraint of the reactants.