from Anten’s SciencesZeolite-based heterogeneous catalysts are used by industrial chemical companies in the interconversion of hydrocarbons and the alkylation of aromatic compounds. A very good example is the zeolite ZS….
Zeolite-based heterogeneous catalysts are used by industrial chemical companies in the interconversion of hydrocarbons and the alkylation of aromatic compounds.
A very good example is the zeolite ZSM-5. This zeolite, developed by Mobil Oil, is an aluminosilicate zeolite with high silica and low aluminum content. Its structure is based on channels with insecting tunnels. The aluminum sites are very acidic. The substitution of Al3+in place of the tetrahedral Si4+ silica requires the presence of an added positive charge. When this is H+, the acidity of the zeolite is very high. The reaction and catalysis chemistry of the ZSM-5 is due to this acidity.
The ZSM-5 zeolite catalyst is used in the petroleum industry for hydrocarbon interconversion.
An example used is in the isomerizations of xylene- from meta to para-xylene. The acidic zeolite promotes carbocation isomerizations.
There are two suggested mechanisms for this type of isomerization.
- Firstly shape may play a role. Perhaps para-xylene has a shape that allows it to diffuse rapidly through the zeolite structure, whereas as meta-xylene takes longer to pass through the zeolite and thus has more opportunity to be converted into the para-xylene.
- Secondly, is that the orientation of reactive intermediates within the zeolite channels favors specifically para-xylene.