Quantitative Zn, Al and H MAS NMR spectroscopy for the characterization of Zn species in ZSM-5 catalysts.

Zn MAS NMR spectroscopy was used to characterize the state of Zn in Zn-modified zeolites ZSM-5. Two Zn enriched zeolite samples were prepared: by solid-state exchange with metal Zn (Zn/ZSM-5 sample) and by ion exchange with zinc formate solution (ZnO/H-ZSM-5 sample), both containing 3.8 wt% Zn.

Tuning the Mechanism of H/D Exchange for Isobutane on H-BEA by Loading Zn Species in Zeolite.

Kinetics of H/D hydrogen exchange between deuterated isobutane-d and Brønsted acid sites (BAS) of three zeolite samples (H-BEA, ZnO/H-BEA, Zn /H-BEA) were monitored with H MAS NMR in situ at 343-468 K. The regioselective H/D exchange in the methyl groups detected on H-BEA can be rationalized in terms of the mechanism of indirect exchange, which involves protonation of the intermediate olefin and further hydride abstraction from the other alkane molecule by the formed carbenium ion. Loading of Zn species in the zeolite results in a decrease of the rate and an increase of the activation energy of the exchange.

Isobutane Transformation to Aromatics on Zn-Modified Zeolites: Intermediates and the Effect of Zn and ZnO Species on the Reaction Occurrence Revealed by C MAS NMR.

To clarify the effects of different Zn species, zeolite topology and acidity (quantity of Brønsted acid sites, BAS) on alkane aromatization, isobutane transformation on Zn /H-ZSM-5, Zn /H-BEA, and ZnO/H-BEA zeolites has been monitored with C MAS NMR. The alkane transformation has been established to occur by aromatization and hydrogenolysis pathways. Zn species is more efficient for the aromatization reaction because aromatic products are formed at lower temperatures on Zn /H-BEA and Zn /H-ZSM-5 than on ZnO/H-BEA.

Dynamics of propene and propane in ZIF-8 probed by solid-state H NMR.

We present a detailed H NMR characterization of molecular mobility of propene and propane propagating though the microporous ZIF-8, a zeolitic imidazolate framework renowned for its outstandingly high separation selectivity for industrially relevant propene/propane mixtures. Experimental characterization of both propene and propane diffusivity in ZIF-8 has been provided. Using H NMR spin relaxation analysis, the motional mechanisms for propene and propane guests trapped within the ZIF-8 framework have been elucidated.

Guests Like Gear Levers: Donor Binding to Coordinatively Unsaturated Metal Sites in MIL-101 Controls the Linker's Rotation.

We present investigation of the effect of electron-donor guests on framework mobility in the metal-organic framework (MOF) MIL-101(Cr) monitored by solid state H NMR spectroscopy. In a guest-free material, the mobile phenylene fragments of the terephthalate (TP) linkers populate two fractions with notably different kinetic parameters for torsional motion. Two fractions of rotational motion are indicative of non-equivalence of TP linker binding to the Cr O trimer, the primary building unit of the MIL-101 framework.