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Rekhtina M, Bugaev A, Dunstan MT, Dal Pozzo A, Nadjafi M, Borca C, Huthwelker T, Abdala PM, Müller CR. Probing the Local Structure of Na in NaNO 3-Promoted, MgO-Based CO 2 Sorbents via X-ray Absorption Spectroscopy. CHEMISTRY OF MATERIALS : A PUBLICATION OF THE AMERICAN CHEMICAL SOCIETY 2023; 35:10060-10069. [PMID: 38107192 PMCID: PMC10720340 DOI: 10.1021/acs.chemmater.3c02077] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/16/2023] [Revised: 11/15/2023] [Accepted: 11/15/2023] [Indexed: 12/19/2023]
Abstract
This work provides insight into the local structure of Na in MgO-based CO2 sorbents that are promoted with NaNO3. To this end, we use X-ray absorption spectroscopy (XAS) at the Na K-edge to interrogate the local structure of Na during the CO2 capture (MgO + CO2 ↔ MgCO3). The analysis of Na K-edge XAS data shows that the local environment of Na is altered upon MgO carbonation when compared to that of NaNO3 in the as-prepared sorbent. We attribute the changes observed in the carbonated sorbent to an alteration in the local structure of Na at the NaNO3/MgCO3 interfaces and/or in the vicinity of [Mg2+···CO32-] ionic pairs that are trapped in the cooled NaNO3 melt. The changes observed are reversible, i.e., the local environment of NaNO3 was restored after a regeneration treatment to decompose MgCO3 to MgO. The ex situ Na K-edge XAS experiments were complemented by ex situ magic-angle spinning 23Na nuclear magnetic resonance (MAS 23Na NMR), Mg K-edge XAS and X-ray powder diffraction (XRD). These additional experiments support our interpretation of the Na K-edge XAS data. Furthermore, we develop in situ Na (and Mg) K-edge XAS experiments during the carbonation of the sorbent (NaNO3 is molten under the conditions of the in situ experiments). These in situ Na K-edge XANES spectra of molten NaNO3 open new opportunities to investigate the atomic scale structure of CO2 sorbents modified with Na-based molten salts by using XAS.
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Affiliation(s)
- Margarita Rekhtina
- Laboratory
of Energy Science and Engineering, Department of Mechanical and Process
Engineering, ETH Zürich, Leonhardstrasse 21, 8092 Zürich, Switzerland
| | - Aram Bugaev
- Paul
Scherrer Institute, Forschungsstrasse 111, 5232 Villigen PSI, Switzerland
| | - Matthew T. Dunstan
- Department
of Chemistry, University of Cambridge, Cambridge CB2 1EW, U.K.
| | - Alessandro Dal Pozzo
- Laboratory
of Energy Science and Engineering, Department of Mechanical and Process
Engineering, ETH Zürich, Leonhardstrasse 21, 8092 Zürich, Switzerland
- Laboratory
of Industrial Safety and Environmental Sustainability, Department
of Civil, Chemical, Environmental and Materials Engineering, Alma
Mater, Studiorum—Università
di Bologna, Via Terracini
28, 40131 Bologna, Italy
| | - Manouchehr Nadjafi
- Laboratory
of Energy Science and Engineering, Department of Mechanical and Process
Engineering, ETH Zürich, Leonhardstrasse 21, 8092 Zürich, Switzerland
| | - Camelia Borca
- Paul
Scherrer Institute, Forschungsstrasse 111, 5232 Villigen PSI, Switzerland
| | - Thomas Huthwelker
- Paul
Scherrer Institute, Forschungsstrasse 111, 5232 Villigen PSI, Switzerland
| | - Paula M. Abdala
- Laboratory
of Energy Science and Engineering, Department of Mechanical and Process
Engineering, ETH Zürich, Leonhardstrasse 21, 8092 Zürich, Switzerland
| | - Christoph R. Müller
- Laboratory
of Energy Science and Engineering, Department of Mechanical and Process
Engineering, ETH Zürich, Leonhardstrasse 21, 8092 Zürich, Switzerland
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