Competitive Pathways of Methane Activation on Zn2+-Modified ZSM-5 Zeolite: H/D Hydrogen Exchange with Brønsted Acid Sites: Versus Dissociative Adsorption to Form Zn-Methyl Species
Full article
| Общее |
Language:
Английский,
Genre:
Full article,
Status:
Published,
Source type:
Original
|
| Journal |
Catalysis Science and Technology
ISSN: 2044-4753
, E-ISSN: 2044-4761
|
| Output data |
Year: 2016,
Volume: 6,
Number: 16,
Pages: 6381-6388
Pages count
: 8
DOI:
10.1039/c6cy00878j
|
| Authors |
Arzumanov Sergei S.
1,2
,
Gabrienko Anton A.
1,2
,
Freude Dieter
3
,
Stepanov Alexander 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 |
Department of Natural Sciences, Novosibirsk State University, Pirogova Street 2, Novosibirsk 630090, Russia
|
| 3 |
Fakultät für Physik und Geowissenschaften, Universität Leipzig, Linnéstraße 5, 04103 Leipzig, Germany
|
|
Funding (3)
|
1
|
Federal Agency for Scientific Organizations
|
V.44.2.11.
|
|
2
|
German Research Foundation
|
HA 1893/16
|
|
3
|
Russian Foundation for Basic Research
|
14-03-00040
|
To clarify the pathways of methane activation on Zn-modified high-silica zeolites, the kinetics of both dissociative adsorption of the alkane C-H bond to form Zn-methyl species and H/D hydrogen exchange between the alkane and Brønsted acid sites (BAS) have been analyzed for Zn2+/H-ZSM-5 containing exclusively Zn2+ cations (no ZnO species in the zeolite) and BAS. Analysis of the kinetics was performed by 1H MAS NMR spectroscopy in situ at 410-540 K. In spite of the activation barrier for H/D hydrogen exchange (68 kJ mol-1) being larger than that for Zn-methyl formation (46 kJ mol-1), the rate of H/D hydrogen exchange has been found to be one order of magnitude higher than the rate of the formation of Zn-methyl species within the studied temperature range. This implies that Zn-methyl species cannot be involved in the reaction of H/D hydrogen exchange as the intermediate responsible for facilitation of this reaction due to the presence of Zn2+ cations in the zeolite (J. Catal., 2008, 253, 11). A new mechanism has been suggested for C-H bond activation in methane on the zeolite modified with Zn2+ cations. It includes first the formation of a transient molecular complex of methane with Zn2+ cations. The complex either is further involved in the reaction of H/D hydrogen exchange or evolves toward the formation of Zn-methyl species and BAS.