Role of Alumina Basicity in CO₂ Uptake in 3‐Aminopropylsilyl‐Grafted Alumina Adsorbents

Abstract

Oxide-supported amine materials are widely known to be effective CO sorbents under simulated flue-gas and direct-air-capture conditions. Most work has focused on amine species loaded onto porous silica supports, though potential stability advantages may be offered through the use of porous alumina supports. Unlike silica materials, which are comparably inert, porous alumina materials can be tuned to have substantial acidity and/or basicity. Owing to their amphoteric nature, alumina supports play a more active role in CO sorption than silica supports, potentially directly participating in the adsorption process. In this work, primary amines associated with 3-aminopropyltriethoxysilane are grafted onto two different mesoporous alumina materials having different levels of basicity. Adsorbent materials with different amine loadings are prepared, and the CO -adsorption behavior of similar amines on the two alumina supports is demonstrated to be different. At low amine loadings, the inherent properties of the support surface play a significant role, whereas at high amine loadings, when the alumina surface is effectively blocked, the sorbents prepared on the two supports behave similarly. At high amine loadings, amine-CO -amine interactions are shown to dominate, leading to adsorbed species that appear similar to the species formed over silica-supported amine materials. The sorbent properties are comprehensively characterized using N physisorption analysis, in situ FTIR spectroscopy, and adsorption microcalorimetry.

Porous Organic Polymers for CO2 Storage and Conversion Reactions

“…Towards this goal, at atmospheric pressure several challenging porous nanomaterials processing high specific surface areas, like POPs, metal‐organic frameworks (MOFs), covalent organic frameworks (COFs), zeolitic imidazole frameworks (ZIFs), amimopropyl‐functionalized porous alumina materials, N‐doped porous carbons, BCN graphene analogues, exhibited remarkable CO 2 uptake property. By tuning the reactive groups present in the monomer units there is huge scope to design a broad range of POPs .…”

Exploring steam stability of mesoporous alumina species for improved carbon dioxide sorbent design

“…This was stirred at 60 o C for 18 h. Separately, 15.54 g of P123 was dissolved in 200 mL of ethanol. This was added to the alumina suspension and stirred at room temperature for 24 h. The sample was then synthesized by heating to 60 o C in an evaporation dish for 48 h. The resulting yellow sample was dried overnight at 75 o C and subsequently calcined at a ramp rate of 1 o C/min to either 400, 550, 700 or 900 o C (as indicated) where it was held for 4 h. This series of species is labelled as "ordered" as it is known to form γ-Al2O3, hence form in an ordered fashion [45].…”

“…The solution was then synthesized by heating to 60 o C for 48 h. The material was then calcined (without further drying) at 400, 550, 700 or 900 o C (as indicated) for 4 h, with a ramp rate of 1 o C/min. This series is labelled as "disordered" as it is not known to be amorphous and not form a specific alumina phase [45].…”

“…S2b) has greater combustible mass than DAl400. For DAl550, the majority of the mass is lost in the 120 -300 o C regime, which is likely due to the sorption of atmospheric species onto its strongly basic sites [45,50], or due to large quantities of surface hydroxyl species on removing the organic components. However, given the total mass lost is around 14 wt%, it is unlikely that this is purely due to the removal of hydroxyl species.…”

“…In our previous work we compared the CO2 uptake of two different class 2 mesoporous alumina supports [45]. One support was 'ordered', with a crystalline γ-Al2O3 structure, with entwinned mesoporous regions, while the other support was 'disordered' with no obvious local structure.…”