TY - JOUR

T1 - Methane Mobility in Ag/H-ZSM-5 Zeolite in the Presence of Ethene

T2 - A View Based on PFG 1H MAS NMR Analysis of Methane Diffusivity

AU - Arzumanov, Sergei S.

AU - Kolokolov, Daniil I.

AU - Freude, Dieter

AU - Stepanov, Alexander G.

PY - 2015/7/28

Y1 - 2015/7/28

N2 - With regard to the influence of methane on the reactivity of ethene on Ag/H-ZSM-5 zeolite, the diffusivities of methane in the presence of ethene coadsorbed on Ag/H-ZSM-5 has been analyzed by PFG 1H MAS NMR spectroscopy. It is established that the diffusion of methane in the absence of ethene occurs more slowly (activation energy Ea = 29 kJ mol-1) than the diffusion of methane in the presence of coadsorbed ethene (Ea = 6-8 kJ mol-1). The higher value of Ea for the methane diffusion in the absence of ethene was related with some strong interaction of methane with Ag+ cations located in the zeolite channel system. Acceleration of diffusion and a decrease of its activation energy in the presence of ethene were assigned to the shielding effect of ethene adsorbed on Ag+ cations to form π-complexes. An absence of direct interaction of methane with Ag+ cations was assumed to provide a significant decrease of activation energy and acceleration of methane diffusion. Two ensembles of methane molecules different by diffusivity have been assumed to exist in the zeolite in the presence of coadsorbed ethene. The presence of two ensembles of diffusing methane in the zeolite was rationalized in terms of the existence of two pathways of methane diffusion through the zeolite channel system. By one pathway, methane presumably diffuses over π-complexes of ethene with Ag+ cations and the zeolite acid OH groups. The other pathway may include the methane diffusion in the zeolite channels exclusively over the zeolite OH groups.

AB - With regard to the influence of methane on the reactivity of ethene on Ag/H-ZSM-5 zeolite, the diffusivities of methane in the presence of ethene coadsorbed on Ag/H-ZSM-5 has been analyzed by PFG 1H MAS NMR spectroscopy. It is established that the diffusion of methane in the absence of ethene occurs more slowly (activation energy Ea = 29 kJ mol-1) than the diffusion of methane in the presence of coadsorbed ethene (Ea = 6-8 kJ mol-1). The higher value of Ea for the methane diffusion in the absence of ethene was related with some strong interaction of methane with Ag+ cations located in the zeolite channel system. Acceleration of diffusion and a decrease of its activation energy in the presence of ethene were assigned to the shielding effect of ethene adsorbed on Ag+ cations to form π-complexes. An absence of direct interaction of methane with Ag+ cations was assumed to provide a significant decrease of activation energy and acceleration of methane diffusion. Two ensembles of methane molecules different by diffusivity have been assumed to exist in the zeolite in the presence of coadsorbed ethene. The presence of two ensembles of diffusing methane in the zeolite was rationalized in terms of the existence of two pathways of methane diffusion through the zeolite channel system. By one pathway, methane presumably diffuses over π-complexes of ethene with Ag+ cations and the zeolite acid OH groups. The other pathway may include the methane diffusion in the zeolite channels exclusively over the zeolite OH groups.

UR - http://www.scopus.com/inward/record.url?scp=84939146820&partnerID=8YFLogxK

U2 - 10.1021/acs.jpcc.5b05953

DO - 10.1021/acs.jpcc.5b05953

M3 - Article

AN - SCOPUS:84939146820

VL - 119

SP - 18481

EP - 18486

JO - Journal of Physical Chemistry C

JF - Journal of Physical Chemistry C

SN - 1932-7447

IS - 32

ER -