STOICHIOMETRY OF THERMOCHEMICAL TRANSFORMATIONS OF NH4Y ZEOLITE

Quantitative aspects of thermal transformations of NH4Y have been investigated using thermogravimetric, temperature-programmed desorption, infrared, and pulsed NMR techniques. Results obtained for hydrated NH4Y agree closely with published data. Anhydrous NH4Y was quantitatively reconstituted from HY. Differential thermograms of ammonium ion decomposition show two distinct classes of chemisorption sites with apparent activation energies of 15 and 22 kcal/mole, respectively. The rate of dehydroxylation is apparently highly dependent on the ambient water vapor pressure. An increase in apparent activation energy from 70 kcal/mole at 10-2 torr to 100 kcal/mole in the presence of He shows that the reaction is probably diffusion-controlled. The N Al atom ratio based on chemisorbed" NH3 is reduced from about 1.0 to 0.5 after dehydroxylation but some NH3 is apparently more strongly held by Lewis-type sites produced. All attempts to reconstitute NH4Y or HY from dehydroxylated zeolite Y failed. © 1968."