Studying of the Mobility of Methane in MFI-Type Zeolites: H-ZSM-5, Ag/H-ZSM-5 and Silicalite-1 by Means of Solid State 2H NMR
4th International School-Conference on Catalysis for Young Scientists “CATALYST DESIGN. From Molecular to Industrial level” (ISCC-2015)
05-06 Sep 2015
|| Khudozhitkov Aleksandr Eduardovich
, Kolokolov Daniil Igorevich
, Arzumanov Sergey Surenovich
, Toktarev Aleksandr Viktorovich
, Stepanov Alexander Grigorʹevich
Boreskov Institute of Catalysis SB RAS
Novosibirsk State University
Zeolites are microporous aluminosillicate materials that are widely used as adsorbents and catalysts. One of the most important representatives of this class of materials is ZSM-5 zeolite. Due to its regular structure and acidity ZSM-5 is eidely used for such reaction types as hydrocarbon izomerization, the alcylation of hydrocarbons and ethylene polymerization. Another good example of ZSM-5 catalytic propeties is given by the reaction of methane dehydro-aromatization on a Mo-modified zeolite . This example underline another useful feature of the zeolites - the possibility to vary the catalytic properties by introduction of the different metal ion sites on the internal surface of the zeolites pores.
One of the most challenging problem in hydrocarbon chemistry is the catalytic transformation of methane. Some of these transformations have been performed on metal enhanced zeolites, particularly on In-ZSM-5. However, the mechanism is still debated. One of the reasons it due to the complex molecular diffusion on methane in zeolites porous network: it is well known that molecular mobility has a crucial meaning for the heterogeneous catalysis since it governs transport of the reagents to the catalytic sites. On common acidic zeolites like H-ZSM-5 the translational mobility of methane was studied by quasi-elastic neutron scattering and NMR pulsed field gradient technique at different loadings. However, the influence of different modifications of the zeolites inner surface on molecular diffusion of methane remains unknown.
In this work molecular mobility of methane has been studied as a function of ZSM-5 zeolite’s modifications: Silicalite-1, H-ZSM-5, Ag-modified H-ZSM-5 and Ag-modified H-ZSM-5 in presence of ethylene molecules with loading equal to concentration of Ag ions. The main goal is to show how gradual complication of the structure leads to the changes of the motion mechanism.
Studying of dynamics was performed by means of the solid state 2H NMR technique. By considering T1, T2 relaxations of the deuterated methane confined in zeolite, we managed to elucidate the mechanism of the reorientation and the characteristic rates and barriers of the motions.