ChemRxiv
These are preliminary reports that have not been peer-reviewed. They should not be regarded as conclusive, guide clinical practice/health-related behavior, or be reported in news media as established information. For more information, please see our FAQs.
MS-MgO-NaNO3-ChemRxiv_28_01_21.pdf (2.44 MB)

Peering into Buried Interfaces with X-Rays and Electrons to Unveil MgCO3 Formation During CO2 Capture in Molten Salt Promoted MgO

preprint
submitted on 27.02.2021, 15:20 and posted on 01.03.2021, 13:00 by Alexander Hansen Bork, Margarita Rekhtina, Elena Willinger, Pedro Castro-Fernández, Jakub Drnec, Paula M. Abdala, Christoph Müller

The addition of molten alkali metal salts drastically accelerates the kinetics of CO2 capture by MgO through the formation of MgCO3. However, the growth mechanism, the nature of MgCO3 formation and the exact role of the molten alkali metal salts on the CO2 capture process remains elusive, holding back the development of more effective MgO-based CO2 sorbents. Here, we unveil the growth mechanism of MgCO3 under practically relevant conditions using a well-defined, yet representative, model system that is a MgO(100) single crystal coated with NaNO3. The model system is interrogated by in situ X-ray reflectometry coupled with grazing incidence X-ray diffraction, scanning electron microscopy and high-resolution transmission electron microscopy. When bare MgO(100) is exposed to a flow of CO2, a non-crystalline surface carbonate layer of ca. 7 Å thickness forms. In contrast, when MgO(100) is coated with NaNO3 MgCO3 crystals nucleate and growth. These crystals have a preferential orientation with respect to the MgO(100) substrate, and form at the interface between MgO(100) and the molten NaNO3. MgCO3 grows epitaxially with respect to MgO(100) and the lattice mismatch between MgCO3 and MgO is relaxed through lattice misfit dislocations. Pyramid shaped pits on the surface of MgO, in the proximity and below the MgCO3 crystals, point to the etching of surface MgO, providing dissolved [Mg2+…O2–] ionic pairs for MgCO3 growth. Our studies highlight the importance of combining X-rays and electron microscopy techniques to provide atomic to micrometer scale insight into the changes occurring at complex interfaces under reactive conditions.

Funding

Advancing CO2 Capture Materials by Atomic Scale Design: the Quest for Understanding

European Research Council

Find out more...

Swiss National Science Foundation, 200020_156015

History

Email Address of Submitting Author

abdalap@ethz.ch

Institution

ETH Zürich

Country

Switzerland

ORCID For Submitting Author

0000-0002-2011-1707

Declaration of Conflict of Interest

There are no conflicts to declare

Exports