Yannick Millot

Quantification of electric-field gradients in the supercage of HY, steam-dealuminated Y and lanthanum-exchanged Y zeolites by 129Xe and 131Xe NMR or physisorbed xenon gas

Abstract The electric-field gradients (EFG) in the supercage of HY, steam-dealuminated Y (STY) and lanthanum-exchanged Y zeolites (LaY) have been quantified using the difference in chemical shift δ CS ( 131 Xe)—δ CS ( 129 Xe) of the two NMR-observable isotopes 131 Xe and 129 Xe. The first, with spin I=3/2, is sensitive to EGF whereas the second, with I=1/2, is not. The EFG values are 15.75×10 19 V/m 2 for HY, 14.30×10 19 V/m 2 for STY and 12.40×10 19 V/m 2 for LaY.

14-P-27-Quantification of electric-field gradients in the supercage of Y zeolites by comparing the chemical shifts of 131Xe (I=3/2) and 129Xe (I=1/2)

Publisher Summary This chapter presents the quantification of electric-field gradients in the supercage of Y zeolites by comparing the chemical shifts of xenon ( 131 Xe) (I = 3/2) and 129 Xe (I =1/2). In the supercages of HY zeolite, the difference in chemical shift (δ cs ( 131 Xe) – δ cs ( 129 Xe)) of the two NMR-observable isotopes 131 Xe, which is sensitive to the electric-field gradient (EFG), and 129 Xe, which is not sensitive to EFG, is -5 ppm at room temperature. The latter value is because of the second-order quadrupole shift of 131 Xe and provides the EFG generated by the framework of this microporous material: 16.3x10 19 V.m -2 .

Quantification of electric-field gradient in the supercage of Y zeolites with 131Xe (I = 3/2) NMR

Les gradients de champs electriques regnant dans les supercages dune zeolithe HY et dune zeolithe Y desaluminee par vapeur deau ont ete obtenus par RMN en utilisant la nutation a une dimension du 131 Xe physisorbe. Ces valeurs sont respectivement de 1,25 et 0,81.10 19 V.m -2 . La sequence dimpulsion composite utilisee pour la detection du signal du 131 Xe annule aussi les signaux parasites appeles ringing, generes par la sonde. Le programme informatique permettant dextraire la constante de couplage quadrupolaire a partir des donnees de la nutation peut etre consulte sur le site web http://www.pascal-man.com.