MECHANISTIC STUDIES OF ISOPENTANE ACTIVATION OVER SOLID ACID CATALYSTS, H-D EXCHANGE WITH USY ZEOLITE, AMORPHOUS SILICA-ALUMINA AND AMBERLYST-15

The mechanism of activation of isopentane on USY zeolite, amorphous si lica-alumina and Amberlyst-15 catalysts was studied by H-D exchange. O nly the zeolite showed exchange with the isopentane at 373 K. The addi tion of 10% of 2-methyl-1-butene to the isopentane accelerates the exc hange with USY zeolite and promotes a small exchange with amorphous si lica-alumina and Amberlyst-15. Nevertheless, the selectivity was diffe rent. With USY, no olefin was detected in the products, suggesting tha t they were protonated (deuterated) to give the tertiary carbenium ion , which, after hydride transfer, desorbs as a deuterated isopentane mo lecule. CP/MAS C-13 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 reactivit y of the zeolite for the reaction with isopentane is probably due to s teric effects, associated with the distortion of the crystalline struc ture, These effects are absents in Amberlyst-15 and amorphous silica-a lumina catalysts.