INFLUENCE OF DEALUMINATION ON THE MICROPORE ADSORPTION IN FCC CATALYSTS

The adsorption of nitrogen and argon on laboratory steam dealuminated and equilibrium commercial FCC catalysts (Y zeolite plus matrix) of va rious types, covering a wide range of catalyst properties, was studied . Different approaches were used to estimate micropore volumes. Microp ore size distributions were assessed based on the area-averaged cylind rical micropore model. With both nitrogen and argon adsorption isother ms, it was possible to locate the peak indicating the pore size in the fresh catalysts at the expected value of 0.74 nm if proper values for the physical parameters in the model were adopted. On the dealuminate d samples, nitrogen and argon yielded significantly different results. Ar-based micropore size distributions suggested that the physical par ameters involved in the model change with the variations in the chemic al composition accompanying dealumination. N-2-based pore size distrib utions are more sensitive to variations in the overall adsorption ener gy due to the growing influence of specific contributions (quadrupolar interactions). The magnitude of the minimum of potential energy in th e nitrogen adsorption process decreases with dealumination up to a sta ble value for Si/Al ratios over about 8. (C) 1997 Elsevier Science B.V .