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.

This paper describes the preparation of pillared montmorillonite by means of mixed aluminum and cerium oligomers. When cerium was incorporated into the materials, the basal spacing increased up to 26 Å. Nuclear magnetic resonance studies indicated total absence of tetrahedral aluminum in the polyoxycations incorporated between the clay sheets. These results indicate that AlCe-pillared montmorillonite incorporates inorganic polyoxycations with a chemical nature different from that of the aluminum polyoxycation or Keggin ion [AlO 4 Al 12 (OH) 24 (H 2 O) 12 ] 7+ . The texture of the materials showed a high specific surface area and porosity, with generation of pores at the limit between the microporous and mesoporous zones. The number and strength of the acid sites in these materials were also high. The catalytic behavior of the materials in the hydrocracking and hydroisomerization reaction of n-heptane was compared with that of materials obtained from the same montmorillonite and intercalation of the Keggin ion. The AlCe-pillared samples showed increased conversion and improved the selectivity toward the products of cracking.

This study compared the textural characterization of montmorillonite pillared with mixed aluminum/ cerium pillars with that of a sample pillared only with aluminum. In addition to the microporosity due to the aluminum pillars, the AlCe-pillared sample exhibited a new porous system, with a pore size at the limit between microporosity and mesoporosity. The pore size distribution determined by the density functional theory and Horvarth-Kawazoe methods allowed estimation of pore volume and indicated two different types of pore in the AlCe-pillared sample. The two types of pore were also observed on t-plot analysis. The presence of larger pores in the AlCe-pillared sample is due to the inorganic polyoxycations intercalated between the clay layers. These polyoxycations are larger than the Keggin ion intercalated in the sample pillared with aluminum alone.

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