Ag 400 Zeolite Molecular Sieves
Strictly speaking, molecular sieves are crystalline silicates or aluminosilicates formed by the linkage of silicon-oxygen or aluminum-oxygen tetrahedra via oxygen bridge bonds.
They possess a system of channels and cavities with molecular-scale dimensions (typically ranging from 0.3 to 2.0 nm), thereby exhibiting the characteristic ability to "sieve" molecules. However, as research into the synthesis and application of molecular sieves has deepened, researchers have discovered aluminophosphate-based molecular sieves. Furthermore, the framework elements of molecular sieves—traditionally silicon, aluminum, or phosphorus—can be substituted by other elements such as B, Ga, Fe, Cr, Ge, Ti, V, Mn, Co, Zn, Be, and Cu; their channels and cavities can also reach sizes exceeding 2 nm. Consequently, based on their framework elemental composition, molecular sieves can be classified into aluminosilicate, aluminophosphate, and heteroatom-substituted framework molecular sieves. Classified by channel size, molecular sieves with channel dimensions of less than 2 nm, between 2 and 50 nm, and greater than 50 nm are termed microporous, mesoporous, and macroporous molecular sieves, respectively. Due to their larger pore diameters, mesoporous materials serve as excellent supports for reactions involving larger-sized molecules; however, the pore walls of mesoporous materials are typically amorphous, meaning their hydrothermal and thermal stability often fail to meet the rigorous conditions required for petrochemical applications.
Because they contain metal ions with low valence and large ionic radii—as well as chemically bound water—molecular sieves undergo a continuous loss of water molecules upon heating, yet their crystalline framework structure remains intact. This process creates numerous cavities of uniform size, which are interconnected by a network of micropores of identical diameter. These minute pores possess a uniform diameter, enabling them to adsorb molecules smaller than the channel diameter into the interior cavities while excluding molecules larger than the channels. Consequently, they can effectively separate molecules based on differences in shape, size, polarity, boiling point, and degree of saturation—essentially performing a "sieving" function on molecules—hence the name "molecular sieve." Currently, molecular sieves are widely utilized across various industries, including metallurgy, chemical manufacturing, electronics, petrochemicals, and natural gas processing.
Silver Molecular Sieve
Ag 400 is a synthetic silver-ion-exchanged molecular sieve engineered for the removal of hydrogen in cryogenic vacuum equipment, distinguished by its superior performance characteristics. It also possesses the capability to selectively remove halogens from gas streams and facilitates catalytic hydrogen-oxygen reactions. This inorganic aluminosilicate material features a crystalline "supercage" structure characterized by pores of uniform diameter. These pores possess open entrances that enable the capture of large quantities of various contaminants, thereby facilitating the full utilization of the catalytic potential of the exchanged silver cations. Ag 400 is primarily employed within cryogenic vacuum vessels to scavenge hydrogen that slowly outgasses from materials—such as stainless steel, carbon steel, and thermal insulation—thereby ensuring the maintenance of an ultra-high vacuum within the vessel.
Molecular sieves typically serve as cryogenic adsorbents, with types 5A and 13X being the most commonly utilized. In contrast, the silver molecular sieve functions as an adsorbent effective at ambient temperatures, specifically designed for the adsorption of hydrogen gas.
