Direct 2H NMR observation of the proton mobility of the acidic sites of anhydrous 12-tungstophosphoric acid.

Flip and hop before you're caught! The proton dynamics of solid 12-tungstophosphoric acid (TPA) is probed by solid-state (2)H NMR in a temperature range from 293-503 K. Protons of TPA are shown to be involved in two types of molecular motion (see picture): the anisotropic local two-site flipping between the two possible orientations of the O-H bond at bridged oxygens of the Keggin anion, and the isotropic diffusion by hopping between neighboring surface oxygens of the anion.

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.

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.