“In terms of maximising low temperature adsorption, porous solid sorbents, such as zeolites, activated carbons, and metal–organic frameworks (MOFs), have certain advantages.29 Unlike chemisorbents, they form weaker non-covalent interactions with the adsorbate, and have lower heats of adsorption (Qst) from 25 to around 50 kJ mol−1, while the Qst for chemisorption can be over 90 kJ mol−1.2,30 Adsorption is exothermic, therefore inversely proportional to temperature, however, where low adsorption temperatures may hinder CO2 uptake for amine-based chemisorbents due to poor diffusion, high surface area physisorbents may excel.31 The different environmental conditions under which chemisorption and physisorption may each be more efficiently deployed is depicted in Fig. 1. An advantage of a physisorbent with weakly adsorbed CO2 may be that it can be more easily regenerated than a chemisorbent.29 Accordingly, an ideal DAC CO2 adsorbent could combine the high selectivity of a chemisorbent, with the lower Qst of a physisorbent to enable efficient low temperature uptake of pure CO2.” https://doi.org/10.1039/D1MA01072G
“Fig. 1 Depiction of physisorption and chemisorption with likely Qst values and physical conditions under which each may be preferred for CO2 capture. (Spheres represent atoms: grey, generic adsorbent; black, carbon; red, oxygen; blue, nitrogen; white, hydrogen.)”