Modification of Fluid Catalytic Cracking Catalysis by the Addition of ZSM-5

Over-cracking of FCC gasoline with either ZSM-5 or REHY results, in both cases, in a preferential loss of heavier olefin components. The major differences between the two zeolites is the increased C3/C4 ratio with ZSM-5 which has been assigned to pore size effects, and enhanced bimolecular hydrogen transfer reactions with REHY, resulting in a higher paraffin/olefin ratio. Typical carbenium ion reaction mechanisms are used to explain the general differences in yields obtained for the two zeolite structures.