MgO-based CO2 sorbents promoted with alkali metal nitrates (e.g. NaNO3) are promising materials for CO2 capture and storage technologies due to their low cost and high theoretical uptake capacities. However, the exact mechanism by which molten alkali metal nitrates promote the carbonation of MgO is highly debated. Therefore, this work aims at elucidating the carbonation mechanism of alkali metal nitrate promoted MgO with the help of oxygen isotope labeling experiments. We show the synthesis of MgO and NaNO3 with high 18O-content. Furthermore, a combination of Raman spectroscopy and in situ thermogravimetrical analysis together with mass spectrometry allows for the tracking of the 18O label in both the solid (NaNO3 and MgCO3) and gas phase (CO2). Our data reveals rapid oxygen exchange reactions occurring during the carbonation. Based on these findings in combination with density functional theory calculations, we discuss potential promotion mechanisms.

Insights on the carbonation mechanism of alkali metal nitrate promoted MgO by oxygen isotope labeling experiments

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