Pillared Tetrasilicic Mica Catalysts Modified by Fixed Interlayer Cations. Classification of Fixation Mode by Cations

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Abstract
Fluor-tetrasilicic mica (TSM) exchanged with various types of cations was calcined at 300 °C for 3 h, and a part of the cations were fixed, followed by Al-pillaring. Thus, acidic pillared clay catalysts were prepared with a modification of the silicate layer by cations. Active catalysts for cumene cracking were obtained when modified by Sr2+, Ca2+, La3+, and Li+. The structural changes in the catalysts affecting the reaction activity was examined through X-ray diffraction, surface area, and 29Si-MASNMR measurements. The mode of cation fixation could be classified into five types, depending on the valence and size of the cations to be fixed. A group-2 cation (Na+) gave no modification effect compared with conventional nonmodified PTSM and managed only meager catalytic activity. The catalyst modified by group-5 by (Sr2+, Ca2+, La3+ etc.) cations or a group-1 (Li+) cation had a distinct pillared structure, characterized by an 18 Å basal spacing. These cations could be fixed either onto the basal oxygen surface for group-5 cations or into the octahedral vacancy for a group-1 cation. Though group-4 (Al3+, Mg2+) and group-3 (Cs+, K+) cations should also be fixed into the vacant sites and onto the surface, respectively, both types of modified catalysts formed unstable pillared structures, giving low catalytic activities.