Pillared Tetrasilicic Mica Catalysts Having Fixed Interlayer Ca Ions. Comparison with Other Clays

Abstract

Abstract Three kinds of Ca2+-modified pillared clays (TSM, taeniolite, and montmorillonite) were prepared from Ca2+-exchanged clays. The cumene cracking activity over the TSM-based catalyst was greatly dependent on the calcination temperature before pillaring, and gave a maximum at 300–400 °C. In contrast, no appreciable increase in the activity with the calcination temperature before pillaring was observed in montmorillonite- and taeniolite-based catalysts. The amount of residual Ca in the modified pillared TSM was increased with a rise in the calcination temperature before pillaring, whereas the amount of Al incorporated through pillaring was decreased, showing the progress of Ca2+ fixation during the stage of thermal treatment of Ca2+-exchanged unpillared TSM. Thus, the cracking activity was greatly enhanced by the fixation of Ca2+. The cracking activity, however, dropped due to a pretreatment above 400 °C, since the Al-pillars which prop silicate layers are reduced while causing a decline in the surface area of the resulting pillared TSM; also, the strong acid sites were decreased due to excessive packing of Ca2+ fixed over the surface of silicate layers. In the cases of montmorillonite and taeniolite, the remaining amounts of Ca and Al were almost constant, irrespective of the calcination temperature before pillaring. This indicates that Ca2+ fixation does not occur in these clays.