Mobility of Stable pi-Complexes of Ethylene with Ag+ Cations in Ag/H-ZSM-5 Zeolite: A H-2 Solid-State NMR Study
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: 2016,
Volume: 120,
Number: 9,
Pages: 4993-5000
Pages count
: 8
DOI:
10.1021/acs.jpcc.5b12687
|
| Authors |
Kolokolov Daniil I.
1,2
,
Arzumanov Sergei S.
1,2
,
Freude Dieter
3
,
Haase Juerger
3
,
Stepanov Alexander G.
1,2
|
| Affiliations |
| 1 |
Boreskov Institute of Catalysis, Siberian Branch of 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
|
Federal Agency for Scientific Organizations
|
V.44.2.11.
|
|
2
|
Russian Foundation for Basic Research
|
14-03-91333
|
|
3
|
German Research Foundation
|
HA 1893/16
|
Ethylene has-been established to form stable pi-complexes with Ag+ cations in Ag-modified zeolite H-ZSM-5 (Ag/H-ZSM-5), which strongly affect the reactivity of ethylene on this catalyst. With the aim Of revealing the catalytic and adsorptive properties of Ag+ cations in Ag/H-ZSM-5, a characterization of the mobility of ethylene pi-complex, located in the zeolite pores, has been performed with H-2 solid-state NMR spectroscopy. Ethylene molecules were established to remain bound to the Ag+ cations at temperatures up to 556 K. In the bound state, ethylene exhibits a H-2 NMR line shape typical for anisotropic motions. It is inferred that being adsorbed on Ag+ cation, ethylene molecule is involved in two internal rotations about its symmetry axes: along the C-2 axis aligned with the C=C bond and about the second C-2' axis orthogonal to the molecule plane. The first rotation occurs with the rate, k(1), of 10-40 kHz and activation barrier E-1 = 2.3 kJ mol(-1), while the second motion occurs with the rate k(2) of 10-400 kHz and E-2 = 4.7 kJ mol(-1). The latter motion is faster than the former One. Both motions occur by four-site jump exchange mechanism. When methane is coadsorbed on the zeolite, the dynamical picture becomes different within two different temperature regions, with T <= 392 K and T > 392 K. Below 392 K, the rotation mechanism is similar to that without methane coadsortion. However, the barrier for the rotation about the C-2' axis increases (E-2(II) = 7.4 kJ mol(-1)), which is evidence for the methane interaction with the ethylene pi-complex. At temperatures as high as 392 K, the 2H NMR line shape of adsorbed ethylene becomes typical for isotropic-like motion. The barrier of the motion, E = 25 kJ mol(-1), is accounted for by involvement of ethylene in the presence of methane in some isotropic or translational motions. At T >= 491 K, the line shape analysis reveals an H/D exchange between C2D4 and CH4.