A combined experimental and simulations assessment of CO₂ capture and CO₂/H₂ separation performance of aminosilane-grafted MCM-41 and pore-expanded MCM-41

Amine-functionalized mesoporous silica materials have attracted considerable attention as robust adsorbents for large-scale CO₂ capture and direct air capture (DAC). Amine grafting increases selective affinity at low pressures, yet also often reduces the adsorbent's pore volume and surface area, affecting the kinetics and capacity upon CO₂ adsorption. MCM-41 and pore-expanded MCM-41 (PE-MCM-41) were developed here, functionalized using 3-aminopropyl triethoxy silane (APTES), and comparably evaluated for their carbon capture performance at different conditions by a combinational experimental, equilibrium and kinetic modelling, and molecular simulations approach. In specific, CO₂ adsorption capacity, CO₂/N₂ selectivity, CO₂ adsorption at humid conditions, heat of adsorption, and regeneration/cyclability were assessed, coupled to molecular simulation insights on the physisorption and chemisorption contribution to the overall adsorption uptake. Indicatively, a capacity value of 3.07 and 2.44 mmol/g was obtained for APTES-PE-MCM-41, and 2.27 and 1.89 mmol/g for APTES-MCM-41, under wet and dry conditions, respectively. The CO₂ selective adsorption from H₂ rich gas streams was also examined over APTES-MCM-41 in order to assess the potential application in H₂ stream purification process. The latter is of high significance in order to use hydrogen as fuel e.g. in anion exchange membrane fuel cells for power production since the presence of CO₂ in the feed composition is considered a major drawback in their commercialization.