Short chain paraffins isomerization on Pt/beta catalysts. Influence of framework and extraframework zeolite composition

Zeolite beta samples with different framework and extraframework composition have been prepared by submitting the acid form of a commercial TEA-beta sample to different post-synthesis treatments, i.e. steam calcination, acid (HCl) leaching, and ammoniums hexafluorosilicate (HFS) treatment. The samples were characterized by XRD, adsorption of N2 at 77 K. i.r. spectroscopy with adsorbed pyridine, 29Si and 27Al MAS-NMR and XPS. Bifunctional catalysts were obtained by impregnation with 0.3 wt% Pt, and the catalytic activity for the isomerization of a simulated LSR feed (n-C5/n-C6, 60/40 wt%) was measured under different reaction conditions. The dealuminated beta catalysts were less active than the parent Hβ sample, but the activity strongly depended on the procedure of dealumination used. Thus, the chemically treated EFAL-free catalysts were much more active than the steam dealuminated EFAL-containing sample. The latter sample contained a reduced number of Brönsted acid sites, mainly due to a charge compensation effect and pore blockage by the EFAL generated during the steam treatment. Furthermore, elimination of the EFAL present in the parent Hβ sample by ammonium hexafluorosilicate treatment produced an increase of the concentration of Brönsted acid sites owing to the mentioned charge compensation effect, but the activity for isomerization of the C5 fraction of the feed decreased. Then, it is suggested that some of the EFAL in Hβ was interacting with the OH groups of framework Al producing Brönsted sites of enhanced activity.