MgO and CaO are widely used for CO2 capture due to their wide
availability in natural minerals, low cost, and easy to produce in
bulk amount. The adsorption and desorption temperatures of
MgO are lower (see below) than those of CaO. CaO-based
materials typically have higher CO2 adsorption capacities
compared to MgO, and thus have been used more intensively.
3.1. MgO
MgO absorbs CO2 in the temperature below 200 C and can
regenerate at relatively low temperatures (500 C) compared to
a CaO-based sorbent.9,22 It has been utilized as a CO2 adsorbent
mainly due to its low energy requirement for regeneration
compared to calcium oxides.8,22,23 However, due to its small CO2
adsorption capacity and the poor thermal stability during
regeneration, the practical application of MgO as a CO2-adsorbent
is limited.9
The adsorption sites for CO2 on MgO are associated with lowcoordinated
O2–Mg2+ sites.24,25–27 The acidic CO2 reacts with
basic O2 sites depending on their coordination. Oxygen atoms
located at edges and corners of the crystal surfaces have stronger
basicity than those in the basal planes.24 CO2 adsorbs as monodentate
on the edge sites and bidentate on the corner sites.28 The
CO2 adsorption capacity of sole MgO is fairly small (2 wt%).29
In order to improve the CO2 capacity of MgO-based adsorbents,
many investigations have been conducted to explore novel MgObased
high-surface-area materials