Influence of dealumination on the micropore adsorption in FCC catalysts

Abstract

The adsorption of nitrogen and argon on laboratory steam dealuminated and equilibrium commercial FCC catalysts (Y zeolite plus matrix) of various types, covering a wide range of catalyst properties, was studied. Different approaches were used to estimate micropore volumes. Micropore size distributions were assessed based on the area-averaged cylindrical micropore model. With both nitrogen and argon adsorption isotherms, 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 dealuminated samples, nitrogen and argon yielded significantly different results. Ar-based micropore size distributions suggested that the physical parameters involved in the model change with the variations in the chemical composition accompanying dealumination. N₂-based pore size distributions are more sensitive to variations in the overall adsorption energy due to the growing influence of specific contributions (quadrupolar interactions). The magnitude of the minimum of potential energy in the nitrogen adsorption process decreases with dealumination up to a stable value for Si/Al ratios over about 8.