Structure of the Hydroxyl Groups and Adsorbed D2O Sites in the DX Zeolite: DFT and Experimental NMR Data

Abstract

We report on density functional theory computations combined with the results of measurements of the quadrupole coupling constants for 17O, hydroxyl deuterons, and adsorbed water deuterons in DX zeolite (n(Si)/n(Al) = 1). Calculations are performed for the crystalline periodic model of the DX zeolite. The local structural parameters are found for various oxygen positions at equilibrium. The quadrupole coupling constants for 17O are in the range CQ(17O) = 7.75 ± 0.5 and 3.75 ± 0.5 MHz for (Si–OD–Al) and (Si–O–Al) substructures, respectively. Related values of the asymmetry parameter η fall in the ranges of 0.9 ± 0.5 and 0.15 ± 0.1, respectively. The quadrupole coupling constant for deuterons depends on the OD distance according to the relation CQ(D)[MHz] = −2.732dOD[MHz/A] + 2.938 MHz. Deuterons are assigned to labeled oxygen positions according to the decreasinng quadrupole coupling constant CQ(D) as O1 ≥ O4 > O2 > O3, with their relative abundances of 54.4, 7.6, 26.6, and 11.4%, respectively. The binding...