Molecular sieves on the basis of crystalline zeolite structures constitute a class of porous substances whose range of applications is due to its unique combination of chemical and physical properties.

A three-dimensions system of channel pores on a molecular (sub-nano) scale, together with a special surface chemistry and a special distribution of cations gives zeolitic molecular sieves the ability to distinguish between molecules of different sizes and with different chemical and physical properties. Therefore they are ideal for highly selective substance separation ("molecular sieving") and/or for substance conversion using adsorptive and catalytic processes.