Thesis (M.Eng.)--Chulalongkorn University, 2003

The effect of particle size in the range of 0.16-2.01 micro m. on the hydrothermal stability of Y zeolite under simulated FCC condition was investigated. The average particle size of 0.45 micro m. was found to be the optimum particle size of Y zeolite to retain high %crystallinity upon hydrothermal treatment as structural destruction caused likely dealumination was confirmed Al[superscript 27] MAS-NMR results. The new correlation was developed by plotting the relative crystallinity (C/Co) against one per the square root of the particle size (d0) of Y zeolite. The correlation accurately predicts the hydrothermal stability of Y zeolite in small to medium particle sizes for a given temperature. For the larger particle sizes of Y zeolite (> 0.45 micro m.), due probably to the presence of more structural defects in the zeolite as shown by higher Bronsted/Lewis acid ratios, no exact correlation between particle size and hydrothermal stability was found by investigation from NH[subscript 3] TPD and pyridine adsorption, respectively.