Microporous silica oxygen adsorption properties

OXYGEN ADSORPTION PROPERTIES OF MICROPOROUS SILICA DERIVED FROM LAYERED SILOXENE BY OXIDATION... 

A high degree of hydrophobic character is an almost unique characteristic of silicon-rich or pure-silica-type microporous crystals. In contrast to the surface of crystalline or amorphous oxides decorated with coordinatively unsaturated atoms (in activated form), the silicon-rich zeolites offer a well-defined, coordinatively saturated sur ce. Such surfrces, based on the strong covalent character of the silicon-oxygen bond and the absence of hydrophilic centers, display a strong hydrophobic character unmatched by the coordinativeiy unsaturated, imperfect surfaces. Also, hydrophobic zeolite crystals have been reported to suppress the water affinity of transition metal cations contained in the zeolite pores. This property permits the adsorption of reactants such as carbon monoxide or hydrocarbons in the presence of water. 

The ability of microporous solids to act as high-capacity molecular sieves has long been exploited in a wide range of applications in adsorption and separation. The electrostatic interactions of the traditional cationic forms of aluminosilicates are well suited for the uptake of polar molecules (such as H2O) and are also able to separate oxygen from air. The development of microporous solids with varied chemistry has enabled adsorption and diffusion properties to be finely tuned for particular technologies. Pure silica zeolite polymorphs such as silicalite have particular importance, because they enable separation on the basis of a different range of polarity and on molecular size the absence of aluminium in the framework also prevents the presence of unwanted acidity, so adsorbed hydrocarbons do not undergo any catalytic transformation. 

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