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)+.
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Data di pubblicazione: | 2009 | |
Titolo: | Mobility of acidic protons in zeolites: A neutron diffraction study of d-heulandite | |
Autori: | Martucci A.; Parodi I.; Simoncic P.; Armbruster T.; Alberti A. | |
Rivista: | MICROPOROUS AND MESOPOROUS MATERIALS | |
Parole Chiave: | Zeolite; Heulandite; Deuterium form; Brønsted acid sites; Neutron powder diffraction; Ion pairs | |
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)+. | |
Digital Object Identifier (DOI): | 10.1016/j.micromeso.2009.03.014 | |
Handle: | http://hdl.handle.net/11392/1379251 | |
Appare nelle tipologie: | 03.1 Articolo su rivista |