¹²⁹Xe NMR on Porous Materials: Basic Principles and Recent Applications

Abstract

A large number of functional and catalytic materials exhibit porosity, often on different length scales and with a hierarchical structure. The assessment of pore sizes, pore geometry, and pore interconnectivity is complex and usually not feasible by classical spectroscopic and diffraction techniques. One of the most powerful methods to probe these parameters is nuclear magnetic resonance (NMR) spectroscopy of xenon, which is introduced into the pore system. Adsorbed to the pore walls, it acts as probe nucleus. In this tutorial review, an introduction into the basic principles of 129Xe NMR spectroscopy and the models developed to determine pore sizes in different materials are given. The possibilities and limitations of this method for obtaining insights into hierarchical structures of functional materials are highlighted and a review of recent works is presented.

Hierarchically‐Ordered Zeolites: A Critical Assessment

“…Hence, it needs to be stated that we are not attempting to discuss the state‐of‐the‐art in assessing transport in hierarchical structure and for this we refer to existing dedicated reviews [ 41,273 ] and articles in this special issue. [ 274,275 ]…”

“…A drawback is inherently low sensitivity of 129 Xe NMR, that, however, can be compensated by xenon hyperpolarization. [ 274 ] Nevertheless, this still requires a dedicated set‐up and is by no means a routine experiment.…”

Heterogeneous Catalysis and Parahydrogen‐Induced Polarization

“…Xenon hyperpolarized by SEOP is widely used as a sensitive probe to study topology of the pore space and surface chemistry of various porous materials. [9] Nuclear hyperpolarization can be also achieved by using parahydrogen -the nuclear spin isomer of hydrogen molecule with a total nuclear spin I = 0. To exploit the spin order of parahydrogen, an additional step is required to break the symmetry of H 2 molecule.…”

“…SEOP has attracted much attention in the field of heterogeneous catalysis as well. Xenon hyperpolarized by SEOP is widely used as a sensitive probe to study topology of the pore space and surface chemistry of various porous materials [9] …”

Xenon Diffusion in Ionic Liquids with Blurred Nanodomain Separation

“…Moreover, structural investigations at the molecular level of hierarchical porous materials, [36,37] pure molecular solvents, [38] several ILs [39,40] and more complex ILs mixture [41,42] rely on 129 Xe NMR spectroscopy. The isotope 129 Xe (spin I=1/2), due to its relatively high natural abundance (26.4 %) and highly polarizable electron cloud (more than 200 ppm chemical shift range) is widely used as a probe to get insights into structural properties of the host materials in the liquid or solid state [43] .…”