Modification of USY zeolites with citric acid

Hydrothermally ultrastablized USY zeolites were further modified with citri c acid in unbuffered systems. The crystal structure, surface area and pore distribution, acid properties and stability in catalytic cracking of modifi ed samples were determined by XRD, N-2-adsorption, FT-IR, DTA techniques re spectively. The micro-activity performance of the modified samples was eval uated on a standard MAT apparatus. The results show that the Si/Al ratio, c rystallinity, lattice constant, and particle size of the modified samples a re all significantly improved The pore system is developed, moreover, the m esopores of the modified zeolites are much great than those of the parent z eolites. The number of acidic sites and the acid strength are consistent wi th those reported in the literature. The present work also shows that modif ied zeolites are promising deep cracking catalyst for producing lighter ole fins (C-3(=) similar to C-6(=) hydrocarbons) with good yield and selectivit y.