H₂O-prompted CO₂ capture on metal silicates in situ generated from SBA-15

A series of metal silicates, NaMSi₁₀Ox (M = Cu, Mn and Ni), were prepared by in situ doping of metals into mesoporous SBA-15 under a hydrothermal process, displaying a continuous framework of SiO₄ structure with a narrow pore size distribution. These metal silicate materials were tested for CO₂ adsorption behavior in the absence and presence of water. The results exhibited that the effect of H₂O on the CO₂ capture capability of metal silicates depends on the types of metal inserted into SBA-15. Compared to the dry condition, H₂O addition enhances CO₂ uptake dramatically for NaCuSi₁₀Ox by 25%, and slightly for NaNiSi₁₀Ox (∼10%), whereas little effect is shown on NaMnSi₁₀Ox. The metal silicate materials are stable after adsorption of CO₂ under wet conditions, which is benefited from their synthesis method, hydrothermal conditions. The improvement of CO₂ uptake on metal silicates by H₂O is attributed to the competitive and synergistic adsorption mechanism on the basis of IR investigations, where initially adsorbed H₂O acts as a promoter for further CO₂ capture through a hydration reaction, i.e., formation of bicarbonate and carbonates on the surface of the samples. These observations provide new possibilities for the design and synthesis of porous metal silicate materials for CO₂ capture under practical conditions where moisture is present.