Octane enhancement with zeolite cracking catalyst - An update

The imminent phasedown of allowable tetraethyl lead content in the gasoline pool to 0.1 g gallon has provided heightened interest in zeolite cracking catalysts specifically designed to upgrade gasoline octane number. Fundamental differences between fluid cracking catalysts available today which perform this function are described. Two classes of molecular sieves are involved; aluminum deficient faujasite types such as ultrastable Y and shape selective zeolites such as silicalite or ZSM-5. Mechanisms by which these two relatively dissimilar families enhance gasoline octane are described and are seen to rely on two vastly different reaction paths. New molecular sieve structures, which will have an effect on cracked product selectivity and quality, are described.