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Why are zeolite catalysts used in fluid catalytic cracking units?

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Aerial view of an oil refinery complex near New Orleans, Louisiana, with storage tanks, industrial structures, and smoke rising from the facility, surrounded by open land. — petroleum refining Aerial view of an oil refinery near New Orleans.

In fluid catalytic cracking (FCC) units, zeolitic catalysts are utilized because they provide more selective yields of desired products while simultaneously reducing the formation of unwanted gas and coke.1

These catalysts, which became common in the industry by the mid-1970s, replaced earlier natural silica-alumina clays. Their effectiveness is largely due to their unique crystalline, porous structure, which allows them to function as molecular sieves. This structure enables the catalyst to selectively adsorb certain molecules while excluding others, facilitating the precise chemical transformations required to convert high-boiling gas oils into valuable, high-octane gasoline. By promoting the carbonium ion mechanism under less severe operating conditions than thermal cracking, zeolitic catalysts significantly improve the efficiency and quality of the refining process.123