Low-temperature activation of branched octane isomers over lanthanum-exchanged zeolite X catalysts

Adsorption and surface chemistry of octane isomers on La-exchanged zeolite X was explored under near-ambient conditions. At low coverage, the sorption constants depend mainly on dispersion forces. However, very strong polarization of the C-H bonds is indicated by an unusually high extinction coefficient of the C-H vibrations. Bi- and tribranched alkanes react under these conditions, and the reactivity increases with the degree of branching. The activation proceeds via hydride abstraction forming alkoxy groups, which subsequently isomerize, and crack. Cracking products desorb primarily via hydride transfer from mobile alkanes leading predominantly to isobutane and isopentane. The surface chemistry and alkanes produced show that adsorption and desorption, cracking and alkylation, as well as hydride-transfer reactions already occur at near ambient conditions in these zeolites.