Abstract: The microporous solids are the key element for a more effective and environment-friendly chemicals production. Especially wide attention have received zeolites-based catalyst due to their stability, catalytic properties and tunability. The tunability can be achieved, either by simply varying the zeolite structure, or by tuning the already chosen pore topology by changing the Al/Si ratio or surface enhancement by metals, oxides, etc. These modifications may have a huge impact of the reaction as they directly change the catalyst active site, however this change is not the only one. The other side of the zeolite framework is the ordered porous network of channels and intersections that constitute the active surface of the zeolite-based catalyst. For most zeolites these channels do not exceed 1-2 nm, i.e. their dimensions are comparable with the size of the adsorbed molecules. As a consequence the transport phenomena plays a crucial role in the reaction pathway: some reagents are able to access only certain sites, while some products are not able to leave the channels. In such situation the knowledge of molecular mobility is essential for a molecular-level understanding and design of new zeolite-based catalysts. In the current work we focus on several specific examples of hydrocarbons mobility in different zeolite systems probed by solid state 2H NMR. On the example of linear alkanes trapped inside 5A zeolite, tert-Butyl alcohol adsorbed into MFI structure (silicalite and H-ZSM5) and ethylene/methane mixture in Ag-enhanced H-ZSM5 zeolites we demonstrate that molecular mobility can be a crucial aspect of the reactions occurring inside zeolite catalysts and how these dynamical phenomena can be tracked down by means of solid state 2H NMR technique. We demostrate that be considering the temperature evolution of 2H NMR spectra line shapes and T1, T2 relaxations of the deuterated hydrocarbons confined inside the zeolite pores we are able to understand both the mechanism of the reorientation and give the characteristic rates and barriers of the motions.

Cite: Kolokolov D.I. , Arzumanov S.S. , Jobic H. , Stepanov A.G.
Experimental Detection of Mobilty of Hydrocarbons in Zeolite-Based Catalysts by Means of Solid State 2H NMR
Catalyst Design: 4th International School-Conference on Catalysis for Young Scientists 05-06 Sep 2015