Effect of the Germanium Incorporation in the Synthesis of EU-1, ITQ-13, ITQ-22, and ITQ-24 Zeolites German Sastre, Angeles Pulido, Rafael Castan ˜ eda, and Avelino Corma* Instituto de Tecnologia Quimica. UPV-CSIC, AV/Los Naranjos s/n, 46022 Valencia, Spain ReceiVed: December 12, 2003; In Final Form: April 20, 2004 Computational chemistry is used here to rationalize zeolite nucleation and crystallization by means of atomistic molecular mechanic techniques. It is shown that, by isomorphous substitution of Ge by Si, the relative rate of crystallization can be reversed in a series of zeolite structures that compete to nucleate and grow under certain synthesis conditions. This is demonstrated for EU-1, ITQ-13, ITQ-22, and ITQ-24 structures. 1. Introduction Organic structure directing agents (SDAs) are commonly used in the synthesis of zeolites to achieve the crystallization of new structures. 1,2 SDAs are important in the nucleation and growth of zeolites, but very seldom do they act as real templates of a particular structure. 3 Indeed, other synthesis variables, such as temperature, water/silica ratio, the presence (or absence) of alkaline cations, the silica mobilizing anion (OH - or F - ), and the nature of framework cations (such as Ge, among others), can be determinant for the particular structure obtained. 4-11 It is then not surprising that, using the same SDA but different alkaline cations (Na + ,K + ), two different structuressSSZ-31 and SSZ-24shave been obtained. 12 Also, with N-benzyl- quinuclidine, either  or SSZ-42 are crystallized when the framework T III cation is either Al or B. 13 Unfortunately, it becomes difficult in most cases to explain the determinant role that variables other than the SDA can play to direct into several close structures. In a very interesting paper, Harris and Zones 14 showed the nature of the interactions between the zeolite microcavity and the SDA, and they related the strength of this interaction, mostly of van der Waals type, with the crystallization time of nonasil and SSZ-13 zeolites. In the present study, we have used hexamethonium as the SDA, which, under the experimental conditions tested, is able to produce EU-1, ITQ-13, ITQ-22, and ITQ-24 zeolites. We study first the pure silica structures and then the effect of germanium and fluorine incorporation, and then how the selectivity of the synthesis is influenced by the short- and long- range interactions of the SDA with the zeolite structure. Moreover, and using the same theoretical methodology, we show that the relative rate of crystallization can be practically reversed when the silica mobilizing agent and the zeolite framework composition is changed. The theoretical results closely match those of the preferred zeolite that has been synthesized and their stability has been measured experimentally. 2. Experimental Section 2.1. Preparation of Hexametilen-bis(trimethylammonium) Dibromide. A quantity of 37.38 g of 1,6-dibromohexane (96% purity, Aldrich), plus 82.35 g of trimethylamine solution (31- 35 wt % in ethanol), and ethanol in the approximate proportion to provide a good mixture, were added to a 500 mL flask, and mixed with a magnetic stirrer for 2 days at ambient temperature. The mixture then was directly washed with ethyl acetate and diethyl ether and the product, hexamethonium dibromide, was recovered using the gravity filtration technique. Afterward, the white solid obtained was left to dry for 12 h at ambient temperature and then stored. 2.2. Preparation of Hexamethonium Dihydroxide. Hex- amethonium dihydroxide was prepared by direct anionic ex- change using a resin, Amberlite IRN-78 (Supelco), as the hydroxide source; the resin was washed with Milli-Q water (Millipore) prior to its use until the water pH was 7. The procedure involved the dissolution of 9 g of hexamethonium dibromide in 250 g of Milli-Q water. The resulting solution was placed into contact with the prior-washed resin into an exchange column, and the flow rate was regulated to obtain an exchange yield of >95%. The solution of hexamethonium dihydroxide was collected into a beaker. This solution was concentrated at 50 °C and kept under vacuum until the hydroxide concentration was >0.05 mol/kg. 2.3. Synthesis of the Boron-Containing ITQ-24 Material. GeO 2 (1.437 g) and 0.204 g of boric acid were dissolved in 161 g of a hexamethonium dihydroxide solution (concentration of 0.256 mol/kg). A quantity (14.311 g) of tetraethylorthosilicate (TEOS) was added to the resulting solution, and the mixture was mechanically stirred at 200 rpm, until the hydrolysis of TEOS had been completed and the ethanol generated was totally evaporated. The final synthesis gel had the following molar composition: where R(OH) 2 is hexamethonium dihydroxide. The gel was autoclaved at 175 °C for 15 days under con- tinuous stirring at 60 rpm, and the solid was recovered by fil- tration, washed with distilled water, and dried at 100 °C overnight. 2.4. Synthesis of the ITQ-22 Material. GeO 2 (0.7185 g) were dissolved in 80.5 g of a hexamethonium dihydroxide solution (concentration of 0.256 mol/kg). TEOS (7.156 g) was added to the resulting solution, and the mixture was mechani- cally stirred at 200 rpm, until the hydrolysis of TEOS had been completed and the ethanol generated was totally evaporated. The final synthesis gel had the following molar composition: where, again, R(OH) 2 is hexamethonium dihydroxide. The gel was autoclaved at 175 °C for 15 days under continuous stirring at 60 rpm, and the solid was recovered by filtration, washed with distilled water, and dried at 100 °C overnight. * Author to whom correspondence should be addressed. E-mail ad- dress: acorma@itq.upv.es. 5SiO 2 :1GeO 2 :1.50R(OH) 2 :30H 2 O:0.12B 2 O 3 5SiO 2 :1GeO 2 :1.50R(OH) 2 :30H 2 O 8830 J. Phys. Chem. B 2004, 108, 8830-8835 10.1021/jp0378438 CCC: $27.50 © 2004 American Chemical Society Published on Web 05/27/2004