Preparation and Characterization of ZSM-5 Zeolites Modified with Titanium and Iron by Direct Synthesis
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Preparation and Characterization of ZSM-5 Zeolites Modified with Titanium and Iron by Direct Synthesis Jessyka Padilla and Verónica García Grupo de Investigación en Química Estructural – GIQUE, Universidad Industrial de Santander, Calle 9 N 27, Bucaramanga, Santander, Colombia ABSTRACT The research for new energy sources has promoted hydrocarbon production from biomass and solid wastes over ZSM-5 zeolites. The metal incorporation by different methods has led to a variety of chemical applications. In this way, the combination of the shape selectivity and acidity properties of the pentasil zeolites with the activity of metal oxide under different environments may influence the product distribution in diverse catalytic reactions. In this work, ZSM-5 zeolites were prepared by hydrothermal synthesis employing aluminum nitrate and AIP as aluminium sources and TPAOH as structure director agent at atmospheric pressure and low temperature (90 ºC). In addition, these materials were modified with iron and titanium cations by direct synthesis at 170 °C and autogenous pressure to promote the crystallinity. The characterization of the samples was performed by XRD, XRF, SEM, TPD-NH3 and nitrogen adsorption. It was observed that the use of AIP and the metal incorporation decreases the crystallinity of the zeolites under synthesis conditions, which leads to increase the specific area value in the BET because of the presence of amorphous material. On the other hand, acidity of the modified zeolites was found to be lower than that of ZSM-5 zeolite. INTRODUCTION The zeolites have received a high interest during recent years because these materials exhibit an elevated superficial area, high adsorption capability, thermal and hydrothermal stability and an ordered-open structure which allows the formation of active sites, considering to the zeolites as a catalyst of diverse reactions at industrial level. The use of zeolites as catalyst has been extended to reforming, cracking, hydrocracking, alkylation reactions, among others [1, 2]. Thus, it has been promoted an increase in the production of new materials through the incorporation of transition metals in the zeolites to improve their properties and accomplish the catalytic demands at present [3]. MFI-type zeolites have become extremely important as shape-selective industrial catalysts, due to their unique porous structure formed by 10 bonded SiO4 and AlO4- tetrahedral, with diameter of 5–6 Å [4, 5]. The ZSM-5 zeolite belong to the MFI-type, and structurally crystallizes in the orthorhombic crystalline system such as Pnma. The zeolites are prepared by hydrothermal synthesis, often employing an organic structure-directing agent, commonly tetrapropylammonium cations (TPA+), which plays an important role in the charge compensating when the substituting ion is trivalent [6]. Therefore, the unit cell of ZSM-5 contains four TPA cations, which are also almost perfectly located in the intersections of the three-dimensional zeolitic channels. On the other hand, the incorporation of transition meta
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