Faujasite

Class: Zeolite, tectosilicate

Related Materials: Zeolites, Linde Type A, Sodalite, Lazurite

Notable Properties: Gas Separation, Hydrocarbon Cracking, Catalysis, Drying Agent, Ion Exchange, Gas Sorption

Crystal structure of Faujasite. Orange spheres represent void space in the sodalite cages.
Crystal structure of Faujasite. Orange spheres represent void space in the sodalite cages.
T-site schematic of the faujasite structure
T-site schematic of the faujasite structure

Description:

Faujasite, (Na2,Ca,Mg)3.5[Al7Si17O48]·32(H2O), can be considered one of the quintessential zeolites given its simplicity in structure, natural occurrence, and the industrial importance of synthetic variants. Faujasite is a colorless rare mineral discovered in 1842 but not used industrially until the mid-20th century. As is evident in the t-site schematic, the faujasite structure can be described as a tiling of sodalite cages connected by double six-ring (d6r) units. This is very similar to the Linde Type A structure where sodalite cages are connected at the square faces by double four-ring (d4r) units.

Industrially, faujasite is sold as either type X or type Y. Zeolite Y is classified as having a silicon to aluminum  ratio of 1:3 or higher and as such are typically less stable. The more anionic the lattice, however, the more strongly guest molecules will interact since there is a higher concentration of charge balancing cations (aluminate is anionic). As such, although the basic structure type is the same the application of Zeolites X and Y are quite different. Type X is a benchmark material for CO2 absorption and separation processes.

In the lab, 13X is a common drying agent used in columns upstream of a Schlenck line or in the catalyst bed of Argon and Nitrogen-filled gloveboxes. It is not in common use for drying solvents were 4A and 3A are preferred.

 

Topology:

FAU

Formula:

(Na2,Ca,Mg)3.5[Al7Si17O48]·32(H2O)

Space Group:

Fd-3m

Unit Cell Parameters:

a = 24.345 Å

Pore Structure:

Small cages (sodalite) with six silicon ring openings with a three-dimensional network of larger one-dimensional channels. Largest included sphere is 11.2 Å and the largest sphere that can diffuse is 7.4 Å.

Occurrence:

Natural and Synthetic (used industrially)

Links:

Database of Zeolite Structures

Wikipedia

Zeomics

 

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