NMR shielding of helium-3 in the micropores of zeolites

In the present work direct measurements of He-3 magnetic shielding were used to investigate helium-3 gas in the micropores of 5 angstrom molecular sieve under pressures up to 300 bar. We have observed the distinct effects in helium-3 shielding when helium gas was interacting with zeolite powder, however these effects cannot be accurately determined due to the unknown bulk susceptibility correction (BSC). The real intermolecular effects in helium-3 shielding are much stronger than it is experimentally observed because the diamagnetic BSC partially cover these effects. As shown the intermolecular interactions are better seen when the quantity of helium-3 is considerably limited at lower pressure and it suggests the presence of dominant interactions between helium-3 atoms and metal ions on surface of the zeolite. We confirm that the use of helium-3 as a probe is promising because this gas has many unique physicochemical properties which allow one to study the smallest micropores in zeolites. Our preliminary results also prove that the measurements of He-3 magnetic shielding provide more precious data than the appropriate NMR chemical shifts. (C) 2014 Elsevier Inc. All rights reserved.