Results of cumene cracking studies over montmorillonite, beidellite, and 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, primarily because it produces much more benzene. This higher activity is consistent with the expectation that beidellite is more acidic, due to the presence of Al in the tetrahedral sheet of this clay mineral. The incorporation of gallium into the beidellite framework reduces its capability to produce benzene. Pillaring with the large cations AlO4Al12(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 considerably. Pillaring montmorillonite increases the benzene yields by a factor of 6, and is critical for higher catalytic activity; beidellite is very active even when unpillared. Isomorphous substitution within the clay layers had less effect than pillaring. The rates of deactivation of the various samples varied considerably. Beidellite pillared with the Ga-13 polyoxocation deactivated very rapidly, presumably because the production of cr-methylstyrene (over the Ga-13 pillars) in the presence of the highly acidic surface of the beidellite resulted in polymerization (coke formation) which poisoned the active sites. The samples most resistant to deactivation were the beidellite samples pillared with Al-13 or GaAl12 cations.