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 [GaO4Al12(OH)(24)(H2O)(12)](7+). Pillaring was per formed with a starting solution having a molar ratio of Al3+/Ga3+ = 12 , which is equivalent to the stoichiometric ratio of this polyoxycatio n. To determine the optimum conditions for obtaining the desired produ ct, we varied the OH-/(Al3+ + Ga3+) molar ratio in the range 1.5-2.5, which also produced variations in the pH of the oligomeric solution. T he most favorable conditions were found to be OH-/(Al3+ + Ga3+) = 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 stabi lity and catalytic behavior of these materials in the hydrocracking an d hydroisomerization of n-heptane have been compared with those of the material obtained from the same montmorillonite by pillaring with the [AlO4Al12(OH)(24)(H2O)(12)](7+) polyoxycation. The structure of the m aterial pillared with the mixed polyoxycation shows higher thermal sta bility and retains 65% of its generated microporosity, up to 700 degre es C. This material also has greater stability in the number and stren gth of the Lewis acid sites of its pillars, resulting in higher select ivity for the isomerization of n-heptane.