Ion-exchanged montmorillonite as simple and effective catalysts for efficient CO₂ capture

One of the main challenges limiting the widespread industrial use of absorbent-based CO₂ capture is the energy intensive solvent regeneration, due to poor CO₂ desorption kinetics. The addition of a catalyst can help optimize the CO₂ desorption rate at low temperatures and minimize the thermal dependence of CO₂ desorption reactions. In this work, we report a new class of inexpensive and abundant montmorillonite clay-based catalysts for this purpose, which can be readily tuned by simple ion-exchange with acid or metal solutions. As an example, in this study montmorillonite was ion-exchanged with an acid, H₂SO₄ and a metal, Zr. The ion-exchange process substantially increased the BET surface area (up to 10 times), mesoporosity, and surface acidity of the parent montmorillonite without noticeably destroying the clay structure. Solvent regeneration experiments at the moderate temperature of 86 °C showed that the catalysts are effective at low temperature, and increased the CO₂ desorption rate by up to 215%, the quantity of desorbed CO₂ by up to 79%, and reduced the relative heat duty by up to 44.15% compared to the benchmark amine solution. Additionally, the prepared catalysts could be easily separated by simple filtration, and their stability was confirmed for five cyclic uses. Finally, based on characterizations and experimental results, a plausible reaction mechanism for the ion-exchanged montmorillonite catalyzed CO₂ desorption reaction is also presented.