Dealumination and characterization of chabazite for catalytic application

Abstract

Dealumination of the small-pore zeolite chabazite (CHA) was performed with ammonium hexafluorosilicate under solid and liquid-state conditions to increase the Si-to-Al ratio from 2.0 to 6.0. In the solid state, the mesopore fraction increased with repeating hydrothermal synthesis at 423 K, which was confirmed by nitrogen adsorption–desorption. In the liquid state, the formation of mesopores decreased substantially and the resulting CHA had an Si-to-Al ratio of ca. 5. The result of desorption of NO–NO2 from the Cu ion-exchanged dealuminated CHA in the solid state indicated that the presence of mesopores reduced NO–NO2 adsorption and desorption of NO2 occurred at 383 and 683 K whereas for the high-silica analog SSZ-13 desorption of NO2 occurred mostly at 473 and at 673 K.