Structural Evolution of Ag-LEV Zeolite upon Heating: an in situ Single-Crystal X-ray Diffraction (SC-XRD) and X-ray Absorption Spectroscopy (XAS) Study

Cametti, Georgia; Scheinost, Andreas; Churakov, Sergey (2020). Structural Evolution of Ag-LEV Zeolite upon Heating: an in situ Single-Crystal X-ray Diffraction (SC-XRD) and X-ray Absorption Spectroscopy (XAS) Study. ACS Omega, 5(49), pp. 31774-31783. American Chemical Society 10.1021/acsomega.0c04455

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Ag-exchanged zeolites are known to have improved sorption and catalytic properties compared to the raw natural material. The application range of Ag-exchanged zeolites is linked to the stability of the exchanged form and its structural evolution at high temperature. In this study, we investigated the thermal stability of an Ag-exchanged zeolite with LEV framework type. The dehydration path was monitored in situ by Single Crystal X-ray Diffraction (SC-XRD) and X-ray Absorption Fine Structure Spectroscopy (XAFS). The experimental data were compared with those extrapolated from Molecular Dynamics (MD) trajectories. Our results showed that Ag-LEV follows a different dehydration path compared to that of the natural levyne (Ca-LEV). Between 25 and 350°C, the unit-cell volume contraction was -4% with respect to that measured at room temperature. Upon dehydration, Ag-LEV transformed to the LEV B topology: such transformation is accompanied by the change from R-3m to R3m space group and by the onset of the rupture of one T-O-T connection at 250°C. Differently from Ca-LEV, no additional change to LEV B’ configuration was detected. XAFS analysis indicated that each Ag is approximately surrounded by 4 oxygen atoms between 2.15 and 2.40 Å. This local environment was maintained up to 650°C. Weak Ag+1-Ag+1 interactions, detected in the whole investigated temperature range, are mainly ascribed to the presence of Ag-erionite (Ag-ERI) intergrown with Ag-LEV. No reduction to elemental Ag0 occurred upon heating.

Item Type:

Journal Article (Original Article)

Division/Institute:

08 Faculty of Science > Institute of Geological Sciences

UniBE Contributor:

Cametti, Georgia; Scheinost, Andreas and Churakov, Sergey

Subjects:

500 Science > 540 Chemistry
500 Science > 550 Earth sciences & geology

ISSN:

2470-1343

Publisher:

American Chemical Society

Language:

English

Submitter:

Georgia Cametti

Date Deposited:

03 Mar 2021 11:49

Last Modified:

07 Mar 2021 03:13

Publisher DOI:

10.1021/acsomega.0c04455

PubMed ID:

33344831

BORIS DOI:

10.48350/152629

URI:

https://boris.unibe.ch/id/eprint/152629

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