Potassium-based sorbents using mesostructured γ-alumina supports for low temperature CO₂ capture

In this work, a series of mesoporous alumina materials exhibiting high surface areas have been synthesized, characterized and used in the preparation of CO₂ sorbents. The mesostructured powders were prepared through a soft chemistry route, employing aluminum tri-sec-butoxide-derived sol precursors in the presence of different surfactants. Structural and microstructural characterization techniques showed that γ-Al₂O₃ powders were composed of nanocrystals, and the samples presented high surface area values (238.6-496.7 m² g^-1) produced by a high mesostructured order, depending on the surfactant used as structure-directing agent. Based on the textural features, selected γ-Al₂O₃ materials were employed as supports for the preparation of potassium-based sorbents for CO₂ capture at low temperatures (30-80 °C). Potassium-loaded alumina supports were synthesized by a wet impregnation method, and the CO₂ sorption tests were conducted via thermogravimetric analysis. The surface area and pore volume of the potassium-impregnated supports experienced a noticeable reduction, in comparison with the original values, suggesting the inclusion of potassium inside the support porosity. Nevertheless, the sorbents showed excellent reactivity; in fact, the potassium/γ-Al₂O₃ sorbent prepared with 40 wt% potassium content had a maximum CO₂ capture capacity of 4.03 mmol CO₂/g sorbent at the relatively low temperature of 80 °C in the presence of water vapor. These results suggest that both the potassium content and textural properties of mesostructured γ-Al₂O₃ supports could provide an enhancement of the CO₂ absorption properties.