Like most zeolites, MCM-22 comprises aluminum, silicon and oxygen atoms. The chemistry associated with zeolite synthesis is quite complex, however, generally speaking they form around large cationic molecules to form an organic intermediate, which is then converted into the end product by treating with high temperature. MCM-22 forms around hexamethyleneimine in the presence of the surfactant cetyltrimethylammonium bromide with the addition of silica and alumina.
MCM-22 is complex, crystalline structure containing a ten and twelve member aluminosilicate ring structure. However, the macrostructure of MCM-22 is dependent on the amount ratios of silica and alumina used in its synthesis.
Apertures with MCM-22 are used as supports for transition metal elements, such as molybdenum. Molybdenum supported MCM-22 is used in the synthesis of benzene from methane. This type of synthesis is called dehydroaromatization and entails the removal of two hydrogen atoms from each methane carbon and the formation of a six-membered delocalized aromatic ring structure. Silicon carbide supported MCM-22 is also used in dehydroaromatization reactions.
Zeolites have a wide range of applications. Some, including Zeolite-A, Zeolite X and Chabazite, are excellent ion exchange agents making them good water softeners in laundry detergents. These and other zeolites are good at absorbing molecules so are used to separate gases and in gas chromatography. Platinum, palladium or rhodium supported on zeolites form the basis of automobile catalytic converters. These heterogeneous catalysts initiate the reduction of harmful nitrogen oxides produced as byproducts of internal combustion to elemental nitrogen and oxygen. Zeolite catalytic converters also oxidize toxic carbon monoxide to carbon dioxide, while their abilities to cleave carbon-carbon bonds means they also break down unburned hydrocarbons present in exhaust gases.