title: Mechanism studies of the conversion of 13C-labeled n-butane on zeolite H-ZSM-5 by using 13C magic angle spinning NMR spectroscopy and GC-MS analysis.
abstract: By using 13C MAS NMR spectroscopy (MAS = magic angle spinning), the conversion of selectively 13C-labeled n-butane on zeolite H-ZSM-5 at 430-470 K has been demonstrated to proceed through two pathways: 1) scrambling of the selective 13C-label in the n-butane molecule, and 2) oligomerization-cracking and conjunct polymerization. The latter processes (2) produce isobutane and propane simultaneously with alkyl-substituted cyclopentenyl cations and condensed aromatic compounds. In situ 13C MAS NMR and complementary ex situ GC-MS data provided evidence for a monomolecular mechanism of the 13C-label scrambling, whereas both isobutane and propane are formed through intermolecular pathways. According to 13C MAS NMR kinetic measurements, both pathways proceed with nearly the same activation energies (E(a) = 75 kJ mol(-1) for the scrambling and 71 kJ mol(-1) for isobutane and propane formation). This can be rationalized by considering the intermolecular hydride transfer between a primarily initiated carbenium ion and n-butane as being the rate-determining stage of the n-butane conversion on zeolite H-ZSM-5.
authors.affiliation: Boreskov Institute of Catalysis, Siberian Branch of the Russian Academy of Sciences, Prosp. Akademika Lavrentieva 5, Novosibirsk 630090, Russia.
authors.forename: Mikhail V
authors.initials: MV
authors.lastname: Luzgin
authors.forename: Alexander G
authors.initials: AG
authors.lastname: Stepanov
authors.forename: Sergei S
authors.initials: SS
authors.lastname: Arzumanov
authors.forename: Vladimir A
authors.initials: VA
authors.lastname: Rogov
authors.forename: Valentin N
authors.initials: VN
authors.lastname: Parmon
authors.forename: Wei
authors.initials: W
authors.lastname: Wang
authors.forename: Michael
authors.initials: M
authors.lastname: Hunger
authors.forename: Dieter
authors.initials: D
authors.lastname: Freude