THE EFFECT OF CYCLIC DEALUMINATION OF MORDENITE ON ITS PHYSICOCHEMICAL AND CATALYTIC PROPERTIES

Commercial Na mordenite was ion-exchanged with both hydrochloric acid and ammonium chloride. The exchanged samples were subjected to three c ycles of hydrothermal/acid treatments, the hydrothermal treatments bei ng performed at 723, 823, and 923 K. Samples having a silica-to-alumin a ratio (SAR) in the range 10.7-100 were prepared. They were character ized by XRD, XRF, Si-29, and Al-27 solid-state n.m.r., t.p.d. of NH3, nitrogen physisorption, and XPS N.m.r. results showed that most but no t all extraframework alumina (EFAL) could be leached with no damage to the zeolite framework. Considerable mesopore formation in the range 3 0-50 Angstrom was observed. Also, the EFAL was shown to block micropor es, mesopores, and strong acid sites. Steaming promoted migration of E FAL to the external surface, whereas leaching rendered the samples rat her homogeneous. The activity for m-xylene isomerization displayed a m aximum as the aluminum content decreased. Catalytic stability increase d with aluminum removal for both n-heptane cracking and m-xylene isome rization.