THE EFFECT OF FRAMEWORK SUBSTITUTION AND PILLAR COMPOSITION ON THE CRACKING ACTIVITIES OF MONTMORILLONITE AND BEIDELLITE

Results of cumene cracking studies over montmorillonite, beidellite, a nd beidellite in which up to 15% of the framework aluminum is replaced with gallium are reported. Under our conditions, the extent of cumene conversion over beidellite is four times that over montmorillonite, p rimarily because it produces much more benzene. This higher activity i s consistent with the expectation that beidellite is more acidic, due to the presence of Al in the tetrahedral sheet of this clay mineral. T he incorporation of gallium into the beidellite framework reduces its capability to produce benzene. Pillaring with the large cations AlO4Al 12(OH)(24) (H2O)(12)(7+), GaO4Ga12(OH)(24) (H2O)(12)(7+), or GaO4Al12( OH)(24) (H2O)(12)(7+) increases the surface areas of these materials c onsiderably. Pillaring montmorillonite increases the benzene yields by a factor of 6, and is critical for higher catalytic activity; beidell ite is very active even when unpillared. Isomorphous substitution with in the clay layers had less effect than pillaring. The rates of deacti vation of the various samples varied considerably. Beidellite pillared with the Ga-13 polyoxocation deactivated very rapidly, presumably bec ause the production of cr-methylstyrene (over the Ga-13 pillars) in th e presence of the highly acidic surface of the beidellite resulted in polymerization (coke formation) which poisoned the active sites. The s amples most resistant to deactivation were the beidellite samples pill ared with Al-13 or GaAl12 cations. (C) 1997 Elsevier Science B.V.