Revealing the mechanism of hydration on the CO2 kinetic adsorption of CaO surface via ReaxFF MD simulations with experiments

NN Wang and YC Feng and X Guo and SX Ma, APPLIED SURFACE SCIENCE, 670, 160652 (2024).

DOI: 10.1016/j.apsusc.2024.160652

Hydration has been regarded as an effective method to improve the cyclic activity of CaO during the Calcium looping CO 2 capture process, but its mechanism remains unclear. In this work, the hydration reaction of CaO surface and its underlying mechanism was studied by ReaxFF molecular dynamics simulation combing with TGA experiments. The effect of hydration on the initial CO 2 adsorption rate showed a trend of promoting at low H 2 O degree and inhibiting at high H 2 O concentration. The CaO surface was easily passivated, and it can maintain its crystal structure and begin to distort at about 1.0 H 2 O monolayer contents. Hydration failed to promote the CO 2 adsorption rate, inversely the CO 2 adsorption process accelerated the diffusion of H ions inward the CaO lattice & sdot;H 2 O dissociation produced two hydroxyl groups: direct O w H and indirect O s H. Atomic density profiles showed that the direct hydroxyl pairs were always, and indirect O s H groups can consume surface oxygen active sites, reducing the initial rapid CO 2 adsorption activity. On the pre-hydrated CaO surface, CO 2 molecules were more likely to bind to solid oxygen active sites than OH groups. The H free radical diffused inside the lattice in the form of transition HO2 state, promoting the slow CO 2 adsorption amount.

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