FAQs

Zeolites are three-dimensional, microporous, crystalline solids with well-defined structures that contain aluminum, silicon, and oxygen in their regular framework; cations and water are located in the pores. The silicon and aluminum atoms are tetrahedrally coordinated with each other through shared oxygen atoms. Zeolites are natural minerals that are mined in many parts of the world; most zeolites used commercially are produced synthetically. Zeolites have void space (cavities or channels) that can host cations, water, or other molecules. Each zeolite framework type has a unique crystal structure which in turn results in a unique network of pores that can be accessible to different molecules.

In 1756, the Swedish mineralogist Axel Fredrick Cronstedt discovered that stilbite, a natural mineral, visibly lost water when heated, and he named the class of materials zeolites from the classical Greek words meaning 'boiling stones.' Zeolites were considered an obscure group of minerals with unique properties for almost 200 years, and Cronstedt was remembered primarily for discovering the element nickel.

During the 1930's, R. Barrer and J. Sameshima did extensive work in zeolite synthesis. In 1948, Richard Barrer first produced a synthetic zeolite that was an analogue of the zeolite mordenite. Shortly thereafter, Milton synthesized the first material that had no natural counterpart, namely zeolite A.

New natural zeolites are still being discovered, and new synthetic zeolites are being invented in many laboratories around the world.

More than 250 unique zeolite framework types have been recognized by the International Zeolite Association.

There are numerous naturally occurring and synthetic zeolites, each with a unique structure. The pore sizes commercially available range from approximately 3 Å to approximately 8 Å. Some of the commercial materials are: A, beta, mordenite, Y, ZSM-5.

Adsorption - Zeolites are used to adsorb a variety of molecules. This includes applications in drying, purification, and separation. They can remove water to very low partial pressures and are very effective desiccants, with a capacity of up to more than 25% of their weight in water. They can remove volatile organic chemicals from air streams, separate isomers and mixtures of gases.

Catalysis – Zeolites can be shape-selective catalysts either by transition state selectivity or by exclusion of competing reactants and products on the basis of their molecular diameters. Zeolites typically contain Bronsted acid sites as active sites but can also be used as supports for active metal cations, metals, metal oxides and Lewis acid sites. The main traditional industrial application areas of zeolites are: petroleum refining, synfuels production, and petrochemical production. Synthetic zeolites are the most important catalysts in petrochemical refineries. Zeolites have also found extensive usage in emission control applications. Recent emerging applications of zeolites include production of renewable fuels and plastic circularity.

The framework aluminum and silicon are bound to each other through shared oxygen atoms. The SiO4 units are neutral: Si+4 / 4 O- but the AlO4 results in a net negative charge: Al+3 / 4O- . The net negative charge is balanced by cations that are present during the synthesis. These cations are highly mobile and can be exchanged for other cationic species.

Zeolite modification implies an irreversible change, unlike ion exchange or adsorption. There are a number of different ways that zeolites can be modified. The framework of the zeolite can be modified by synthesizing zeolites with metal cations other than aluminum and silicon in the framework. The framework of the zeolites can be modified by dealumination to increase the silica and increase the hydrophobic nature of the zeolite. There are many proprietary methods to modify zeolites that impart unique characteristics to them.

Many zeolites are thermally and hydrothermally stable to over 500 °C. Some are stable in an alkaline environment, and some are stable in acidic media. They are also stable to ionizing radiation and can be used to adsorb radioactive cations.

Zeolites can separate molecules based on size, shape, polarity, degree of unsaturation, among others.

Zeolites can be regenerated using relatively easy methods such as heating to remove adsorbed materials, ion exchanging with sodium to remove cations, or pressure swing to remove adsorbed gases. The ease of regeneration depends on the application.

Zeolites are available as powders or as formed products such as extrudates. Zeolites, like other solids, are safe to handle and are easy to use in a variety of reactors.

The combination of many properties, among them: the microporous character of the uniform pore dimensions, the ion exchange properties, the ability to develop internal acidity, the high thermal stability, the high internal surface area. These make zeolites unique among inorganic oxides.

Not all zeolites have been studied, but extensive studies have been done on zeolite A due to its use in consumer products. These studies have demonstrated that type A zeolite is essentially non-toxic via oral, dermal, ocular, and respiratory routes of exposure; type A zeolite was also found to be safe for the environment. Please consult the SDS for product(s) of interest.