Mechanistic studies of isopentane activation over solid acid catalysts. H-D exchange with USY zeolite, amorphous silica-alumina and Amberlyst-15 Original Research Article

The mechanism of activation of isopentane on USY zeolite, amorphous silica-alumina and Amberlyst-15 catalysts was studied by H-D exchange. Only the zeolite showed exchange with the isopentane at 373 K. The addition of 10% of 2-methyl-1-butene to the isopentane accelerates the exchange with USY zeolite and promotes a small exchange with amorphous silica-alumina and Amberlyst-15. Nevertheless, the selectivity was different. With USY, no olefin was detected in the products, suggesting that they were protonated (deuterated) to give the tertiary carbenium ion, which, after hydride transfer, desorbs as a deuterated isopentane molecule. CP/MAS13C NMR analysis of the zeolite after exchange showed a significant amount of adsorbed olefinic material. On the other hand, the main reaction on Amberlyst-15 and silica-alumina is the apparent isomerization of 2-methyl-1-butene to 2-methyl-2-butene. The reactivity of the zeolite for the reaction with isopentane is probably due to steric effects, associated with the distortion of the crystalline structure. These effects are absents in Amberlyst-15 and amorphous silica-alumina catalysts.