Effect of dealumination severity on the pore size distribution of mordenite

Acid leaching with nitric acid was conducted for the framework dealumination of H-mordenite. The parent as well as the samples obtained after acid treatment were characterized by XRD, surface area, pore volume and pore size distribution for identifying structural changes after dealumination. For the parent (HM) and two acid leached (ATHM-1 and ATHM-3) samples studied, the surface area and micro pore volumes were increased in the order of HM < ATHM-1 < ATHM-3. Nitrogen adsorption studies at 77 K indicated that the increase in micro pore volume is not uniform for the pores of diameter 0–20 Å, where the entire range of micropores were classified into three groups, namely smaller micropores belong to side pockets, micropores belong to main channels, and the secondary micropores that are larger than main channels. The pore volume in small and larger micropores was increased, where as that of the main channels was decreased in the order of HM < ATHM-1 < ATHM-3, and the detailed analysis could provide a direct evidence for the opening of side pockets of mordenite by acid dealumination. The dealuminated samples ATHM-1 and ATHM-3 exhibited enhanced n-hexane isomerization activity.