Estudio preliminar de la síntesis de ferritas de cobalto cubiertas por una capa mesoporosa de silicalita de titanio con potencial aplicación para reacciones de oxidación selectiva: : estudio preliminar de la influencia de la relación molar de bromuro de hexadeciltrimetilamonio (CTAB) CTAB/(Ti+Si) en la síntesis de ferritas de cobalto cubiertas por una capa densa de sílice y una capa mesoporosa de silicalita de titanio.

Abstract

Titanium silicalite catalysts are commonly used in olefin oxidation. One of the most utilized methods to obtain this type of material is the "sol-gel" approach, which involves the use of surfactants (e.g. CTAB) as templating agents. The aim of this study was to examine the influence of the molar ratio of hexadecyltrimethylammonium bromide (CTAB) CTAB/(Ti+Si) on the synthesis of cobalt ferrites covered by a dense layer of silica and a mesoporous layer of titanium silicalite. The synthesis of the magnetic core, cobalt ferrite, was conducted via hydrothermal route using iron nitrate and cobalt nitrate as precursors. On the other hand, the mesoporous layer of titanium silicalite was synthesized through the sol-gel method, assisted by the hydrothermal route. In this process, along with titanium butoxide and silicon ethoxide, two different values of the CTAB molar ratio were employed. The two synthesized catalysts were characterized by X-ray Diffraction (XRD), Atomic Absorption (AA), Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR), Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES), and nitrogen physisorption. Furthermore, catalytic tests in the oxidation of styrene were conducted over a 6-hour period, and conversion was monitored using gas chromatography. The specific surface areas of the catalysts FCR_CTAB 0.31 and FCR_CTAB 0.35 were 327 and 568 m2/g, respectively. The catalyst synthesized with the CTAB molar ratio of 0.35 exhibited lower titanium content, explaining the decreased in styrene conversion despite having a higher specific surface area. In contrast, the catalyst with the CTAB molar ratio of 0.31 displayed the highest conversion of styrene (28 %). Although CTAB increased the surface area, it also negatively affected the titanium insertion into the silicalite framework. Consequently, the decline in the synthesized catalyst's catalytic activity was attributed to the elevated CTAB/(Ti+Si) ratio.