Preparation of Mesoporous SiO2-Pillared Lamellar Titanoniobate Catalysts for Bioethanol Dehydration

The lamellar perovskite K0,8Ti0,8Nb1,2O5 was prepared by solid state reaction, and its protonic form was used in a sequence of intercalation steps with n-butylamine, cetyltrimethylammonium bromide (CTABr), and tetraethyl orthosilicate (TEOS). After calcination, a high surface area, mesoporous SiO2-pillared titanoniobate, was obtained. The samples were characterized by XRD, EDX, TG-DTG, N2 adsorption isotherms, and NH3-TPD. The pillarization procedure affected the textural properties, the amount, and strength distribution of acid sites. The influence of the pillarization procedure on the catalytic properties of the lamellar titanoniobates was investigated on ethanol dehydration. High ethanol conversions and ethylene yields (>90%) were obtained in the presence of the SiO2-pillared titanoniobate catalyst, at 350–450°C. 1. Introduction Since the last decades, the intercalation chemistry of lamellar materials has been used as a strategy either to modify or produce innovative materials designed for some special applications [1]. In this sense, clays, graphite, some halides or oxides of transition metals, phosphates, and sulfides have been investigated as host materials to produce semiconductors, sensors, electrodes, catalysts, photocatalysts, and so forth [2–7]. Potassium titanoniobate, KTiNbO5, is a lamellar perovskite built up of edge sharing and octahedral forming strings that are connected by sharing corners to form a layered structure intercalated with alkaline cations (K+), which compensate the negative charge in the interlayer space [8]. This material can be synthesized by solid state reaction, but some studies hve been published recently showing that KTiNbO5 can be prepared by hydrothermal synthesis at lower temperatures with different particle sizes and morphologies, depending on the solvent used during the process [9]. Independently of the synthesis method, interlayer K+ cations are exchangeable, allowing the intercalation of species of different sizes that result in a variety of composites of improved properties [8]. For example, substitution of K+ by H+ cations produces HTiNbO5 that can be a strong Br？nsted acid comparable to some zeolites [10]. In spite of this, the use of this protonic form as a heterogeneous acid catalyst is still limited by textural properties, such as low surface area and porosity [11]. Exfoliation of KTiNbO5 or HTiNbO5 has been investigated, but the resultant colloids are adequate only for photocatalytic purposes [12]; but for traditional heterogeneous acid-catalyzed processes it would be necessary to precipitate the