Methane Interaction with Zn2+-Exchanged Zeolite H-ZSM-5: Study of Adsorption and Mobility by One- and Two-Dimensional Variable-Temperature 1H Solid-State NMR
Full article
| Общее |
Language:
Английский,
Genre:
Full article,
Status:
Published,
Source type:
Original
|
| Journal |
The Journal of Physical Chemistry C
ISSN: 1932-7447
, E-ISSN: 1932-7455
|
| Output data |
Year: 2015,
Volume: 119,
Number: 25,
Pages: 14255-14261
Pages count
: 7
DOI:
10.1021/acs.jpcc.5b04028
|
| Authors |
Luzgin M.V.
1,2
,
Freude D.
3
,
Haase J.
3
,
Stepanov A.G.
1,2
|
| Affiliations |
| 1 |
Boreskov Institute of Catalysis, Siberian Branch of the Russian Academy of Sciences, Prospekt Akademika Lavrentieva 5, Novosibirsk
630090, Russia
|
| 2 |
Faculty of Natural Sciences, Department of Physical Chemistry, Novosibirsk State University, Pirogova Street 2, Novosibirsk 630090,
Russia
|
| 3 |
Fakultat fur Physik und Geowissenschaften, Universitat Leipzig, Linne ̈ strasse 5, 04103 Leipzig, Germany
|
|
Funding (3)
|
1
|
Russian Foundation for Basic Research
|
14-03-91333
|
|
2
|
German Research Foundation
|
HA 1893/16
|
|
3
|
Russian Foundation for Basic Research
|
14-03-00040
|
Acidic zeolites in which protons are substituted (completely or in part) by metal cations demonstrate higher activity in catalytic reaction of light alkanes conversion in comparison with parent zeolites. The study of alkane adsorption on metal cationic species as the first stage of alkane interaction with the active sites of zeolites is crucial for understanding the mechanism of light alkane activation on metal-containing zeolites. By using variable-temperature 1H magic-angle spinning nuclear magnetic resonance (1H MAS NMR), the adsorption of methane on Zn2+-exchanged H-ZSM-5 zeolites (Zn2+/H-ZSM-5) with different Zn2+ content, as well as on source H-ZSM-5, has been studied at 333–463 K. The enthalpy of adsorption (ΔHads) on different centers, acid-bridged OH groups and Zn2+ cations, has been determined to be −18.6 ± 0.4 kJ mol–1 for OH groups and from −10.9 to −11.7 kJ mol–1 for Zn2+ cations of both Zn2+/H-ZSM-5 zeolite samples studied. Two-dimensional 1H MAS exchange NMR experiments revealed the chemical exchange between the adsorbed and gas-phase methane molecules at 353–463 K with the effective rate constant of 10–60 s–1. The increase of Zn2+ content leads to a decrease of the exchange rate, whereas the apparent activation energy (Ea) of the exchange increases from 13 kJ mol–1 for H-ZSM-5 zeolite to 20 and 23 kJ mol–1 for the samples, in which 50% and 85% of acid protons, respectively, were substituted by Zn2+cations. Variation of Ea for samples with and without Zn2+ cations was interpreted in terms of internal transport barriers that can exist at the intersections between the elementary building blocks of the crystals and/or between the crystal intergrowths in crystals of our zeolite samples. Additional transport barriers can arise from the bulky Zn2+ cations, located at the entrances of the zeolite pore system on the crystal surface.