The development of better adsorbent materials for CO2 capture is one of the favored options to mitigate anthropogenic CO2 emissions. In the past few years, this objective has fostered significant research efforts in the field of materials sciences, with hundreds of new solids of potential value for CO2 capture being proposed every year. However, this frenetic research for new solid adsorbents could be more efficient if we had a clearer idea of what we are looking for, i.e. if we could define the characteristics of the optimal solid. As part of a thesis project, IFPEN teams, working with CPE Lyon, have been trying to sketch a portrait of this optimal solid.
Let us explain the research strategy that was adopted: in the vast majority of cases, CO2 is emitted in mixture with other gases. An adsorption-based CO2 capture process separates CO2 from the gas mixture in the following way:
The process involves repeated cycles of alternating high-pressure adsorption and low-pressure desorption, hence its name: "Pressure Swing Adsorption" (PSA).
To develop an ideal material for the PSA process, it is necessary to tune the interaction force between the solid and CO2 versus the other ingredients present in the gas mixture. The interaction forces between the CO2 and the solid must be strong enough to adsorb large quantities of CO2 (and do so selectively with respect to the other ingredients in the gas mixture), but not too strong in order to facilitate the recovery of CO2 during the desorption phase. The first scientific challenge was to define the value of this optimal force .
But once this first important step had been achieved, it was still not clear what the solid that would offer this optimal interaction force would look like. CPE Lyon and IFPEN researchers therefore developed statistical thermodynamic models enabling them to link the forces involved (electrostatic and Van der Waals bonds) to simple descriptors of the adsorbent solid: its pore size, the shape of these pores , the chemical composition of its surface, the distribution of electrostatic charges in space. Via these models, it is therefore possible to define the optimal pore size range  and the associated charge distribution .
The conclusions extracted from the model helped guide and limit the choice of solids studied experimentally and thus led to the rapid identification of two zeolites exceeding the performance of conventional adsorbents in medium-pressure CO2 capture.
Principles and approach adopted
in the optimal adsorbent determination model
 García, Edder J.; Pérez-Pellitero, Javier; Pirngruber, Gerhard D.; Jallut, Christian; Palomino, Miguel; Rey, Fernando; Valencia, Susana (2014) Industrial & Engineering Chemistry Research, vol. 53, n° 23, p. 9860–9874.
>> DOI: 10.1021/ie500207s
 García, Edder J.; Pérez-Pellitero, Javier; Jallut, Christian; Pirngruber, Gerhard D. (2013) Physical chemistry chemical physics : PCCP, vol. 15, n° 15, p. 5648–5657.
>> DOI: 10.1039/c3cp44375b
 García, Edder J.; Pérez-Pellitero, Javier; Jallut, Christian; Pirngruber, Gerhard D. (2013) Langmuir : the ACS journal of surfaces and colloids, vol. 29, n° 30, p. 9398–9409.
>> DOI: 10.1021/la401178u
 García, Edder J.; Pérez-Pellitero, Javier; Jallut, Christian; Pirngruber, Gerhard D. (2014) The Journal of Physical Chemistry C, vol. 118, n° 18, p. 9458–9467.
>> DOI: 10.1021/jp500209v
Scientific contact: email@example.com