Problems with molecular sieves in adsorbing CO2

Zeolite molecular sieves are hydrated crystalline silicoaluminates that possess uniform micropores with sizes comparable to those of typical molecules. Since their pore sizes allow them to separate molecules of different sizes, they are known as zeolite molecular sieves. It is sometimes also called molecular sieve zeolite, foamed zeolite, or molecular sieve. It possesses a unique regular crystal structure, in which each type of zeolite features pore structures of specific size and shape, as well as a high specific surface area. Most zeolite molecular sieves have strong acid sites on their surfaces, while a strong Coulombic field within the crystal pores exerts a polarizing effect. The chemical composition is: M (2/n) O * Al2O3 * m SiO2 * p H2O. Here, M represents a metal cation or an organic cation; n is the valence of the metal cation; m is the amount in moles of SiO2, which is numerically equal to the molar ratio of SiO2 to Al2O3 – this ratio is also referred to as the silica-alumina ratio. The number of moles of H2O. Its characteristics are as follows: 1. Due to the open skeletal structure of zeolite molecular sieves, it possesses a high adsorption capacity. Different silicon-aluminum ratios can result in hydrophilicity and hydrophobicity. Generally, zeolites with a low Si/Al ratio have strong electrostatic fields in their pores, making them prone to adsorbing polar molecules. Such as type A zeolite. Conversely, zeolites with a high silica-alumina ratio have no electrostatic field in their pores, resulting in weak polarization capacity; the interaction between the adsorbate and the zeolite is mainly due to dispersion forces. For example, HZSM-5 type. 2. The regular microporous crystal structure possesses unique shape-selective adsorption properties. 3. Ion exchange properties. For more details, please refer to “Catalysts and Catalysis”, edited by Wang Guiru

I don’t know. All I know is that molecular sieves can adsorb water, carbon dioxide, acetylene and other hydrocarbons, but they cannot adsorb methane, ethane, etc

Molecular sieves inherently possess a certain adsorption selectivity for adsorbates, which allows them to adsorb carbon dioxide.

Overall, CO2 is linear, non-polar, with a dipole moment of zero. However, the carbon-oxygen bond is highly polar, with the electron cloud of this bond shifting significantly toward oxygen. From this perspective, it can be considered that the CO2 molecule has positive charges at both ends and a negative charge in the middle; these charges are exposed and thus capable of interacting with the oppositely charged sites on the adsorbent, thereby enabling adsorption. From another perspective, the oxygen atoms in CO2 molecules possess lone pairs of electrons; therefore, CO2 molecules can be regarded as Lewis bases (according to the acid-base electron theory), while the metal cations on molecular sieves can be considered as acidic sites (Lewis acids). Therefore, the adsorption of CO2 molecules on molecular sieves can be considered as a coordination reaction (or complexation reaction) between Lewis acids and bases

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