Molecular sieves possess three core properties

1.Molecular sieving performance

Molecular sieves feature an extremely uniform pore size distribution. Only substances with molecular diameters smaller than the pore size can enter the internal cavities of the molecular sieve crystals. For instance, 3A molecular sieves have a pore size of approximately 0.3 nanometers, allowing only water molecules (about 0.27 nanometers in diameter) to pass through while repelling larger molecules (such as propane, around 0.43 nanometers). 5A molecular sieves, with a pore size of roughly 0.5 nanometers, are used for separating oxygen (0.34 nanometers) and nitrogen (0.36 nanometers). This precise "molecular screening" capability makes them key materials for separation and purification processes.

2.Adsorption performance

Even if molecules are smaller than the pore size, molecular sieves preferentially adsorb polar molecules (such as water and carbon dioxide) and unsaturated molecules (such as alkenes) through van der Waals forces or hydrogen bonds on the pore surface. This further enhances sieving precision. For example, nitrogen production using carbon molecular sieves achieves efficient nitrogen separation by preferentially adsorbing oxygen (which has slightly stronger polarity).

3.Catalytic performance

The pore structure of molecular sieves serves as "microreactors" for chemical reactions. The acidic sites on their surface (generated by the charge balance between the negative charge of aluminum-oxygen tetrahedra and cations) can catalyze carbocation-type reactions. For instance, Y-type molecular sieves, as petroleum cracking catalysts, can crack heavy oil into light fuels like gasoline. They are currently one of the most widely used catalysts in the petroleum refining industry.

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