Dealumination of zeolites .6. Influence of the hydrothermal treatment of EMT zeolites on their framework composition and on their porosity

The hydrothermal treatment in a flow reactor of NH(4)NaEMT zeolite samples was carried out in order to determine quantitatively the effect of the operating conditions (time and temperature) and of the degree of sodium exchange by ammonium cations (from 70 to 100%) on the percentage of dealumination, Linear correlations established between the wavenumbers of the IR double 6 ring band or the unit cell parameters determined by XRD and N-Al, the number of framework aluminum atoms per unit cell determined by Si-29 NMR, were used to estimate N-Al of the steamed samples. Only the aluminium atoms associated with NH4+ (and not Na+) could be extracted from the framework. Moreover sodium cations had an inhibiting effect on the zeolite dealumination. The dealumination of EMT-type zeolites was faster than that of FAU-type samples with identical compositions. Steaming of NH(4)NaEMT samples had only a limited effect on their crystallinity, estimated by XRD, and on their micropore volume accessible to nitrogen. It caused the formation of mesopores with a diameter of 6 - 9 nm. Mild acid washing allowed to eliminate extraframework aluminium species responsible for a limited blockage of the access of nitrogen to the EMT micropores.