Neutron Rietveld refinement of a natural heulandite (Si/Al = 3.1) in its deuterium form was performed in space group C2/m. Two Brønsted acid sites were identified. One was on framework oxygen O1, occupied to 20% and headed toward the center of the 8-membered ring channel running parallel to [1 0 2]; the other was on O6, occupied to 30% and headed toward the 10-membered ring channel running parallel to the c-axis. Three other extraframework sites, located around a distance of 3 Å from the framework oxygens, were attributed to reabsorbed H2O molecules. On the whole, about 3.2 Brønsted acid sites were located representing about 37% of the value expected on the basis of the aluminium content. This discrepancy is attributed to proton transfer from the Brønsted site to reabsorbed H2O molecules, forming either a hydroxonium ion (H3O+) or charged clusters such as (H5O2)+ and (H7O3)+.

Mobility of acidic protons in zeolites: A neutron diffraction study of d-heulandite

MARTUCCI, Annalisa;PARODI, Ilaria;ALBERTI, Alberto
2009

Abstract

Neutron Rietveld refinement of a natural heulandite (Si/Al = 3.1) in its deuterium form was performed in space group C2/m. Two Brønsted acid sites were identified. One was on framework oxygen O1, occupied to 20% and headed toward the center of the 8-membered ring channel running parallel to [1 0 2]; the other was on O6, occupied to 30% and headed toward the 10-membered ring channel running parallel to the c-axis. Three other extraframework sites, located around a distance of 3 Å from the framework oxygens, were attributed to reabsorbed H2O molecules. On the whole, about 3.2 Brønsted acid sites were located representing about 37% of the value expected on the basis of the aluminium content. This discrepancy is attributed to proton transfer from the Brønsted site to reabsorbed H2O molecules, forming either a hydroxonium ion (H3O+) or charged clusters such as (H5O2)+ and (H7O3)+.
Martucci, Annalisa; Parodi, Ilaria; Simoncic, P.; Armbruster, T.; Alberti, Alberto
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11392/1379251
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