Differences in Structural, Textural, and Catalytic Properties of Montmorillonite Pillared with (GaAl12) and (AlAl12) Polyoxycations

This paper reports the preparation of a pillared montmorillonite using the mixed oligomer [GaO 4 Al 12 (OH) 24 (H 2 O) 12 ] 7+ . Pillaring was performed with a starting solution having a molar ratio of Al 3+ /Ga 3+ = 12, which is equivalent to the stoichiometric ratio of this polyoxycation. To determine the optimum conditions for obtaining the desired product, we varied the OH - /(Al 3+ + Ga 3+ ) molar ratio in the range 1.5−2.5, which also produced variations in the pH of the oligomeric solution. The most favorable conditions were found to be OH - /(Al 3+ + Ga 3+ ) = 2.0 and pH = 3.7. The presence of mixed polyoxycations in the pillars of the synthesized materials was confirmed by NMR studies. The thermal stability and catalytic behavior of these materials in the hydrocracking and hydroisomerization of n -heptane have been compared with those of the material obtained from the same montmorillonite by pillaring with the [AlO 4 Al 12 (OH) 24 (H 2 O) 12 ] 7+ polyoxycation. The structure of the material pillared with the mixed polyoxycation shows higher thermal stability and retains 65% of its generated microporosity, up to 700 °C. This material also has greater stability in the number and strength of the Lewis acid sites of its pillars, resulting in higher selectivity for the isomerization of n -heptane.