Enhancement of Dehydrogenation and Hydride Transfer by La3+Cations in Zeolites during Acid Catalyzed Alkane Reactions

Abstract

La3+ cations exchanged into ultrastable zeolite Y and zeolite X promote catalytic isomerization, cracking, and alkylation of alkanes. La3+ cations stabilize the zeolite lattices and, more importantly, polarize alkane C–H bonds to enhance the rates of all three reactions. This unique activity leads to stable cracking and isomerization of reactive alkanes, with polarizable C–H bonds with adjacent tertiary or quaternary carbon atoms below 370 K. The presence of La3+ cations also enhances the zeolite catalyzed hydride transfer rate for isobutane alkylation with 2-butene leading to high catalyst stability. Solid state MAS NMR shows that the strongest positive effects are associated with nonhydroxylated La3+ cations accessible to the reacting molecules in supercages of the zeolite. The high activity is the result of a cooperative polarization of C–H bonds of alkanes by La3+ cations and the presence of stable and strong Bronsted acid sites.