Transesterification reaction of vegetable oils, using superacid sulfated TiO 2 –base catalysts Rusiene M. de Almeida a, *, Lu ´ cia K. Noda b , Norberto S. Gonc ¸alves b , Simoni M.P. Meneghetti a , Mario R. Meneghetti a a Instituto de Quı´mica e Biotecnologia, Universidade Federal de Alagoas, Av. Lourival de Melo Mota, s/n, Maceio ´ 57072-970, AL, Brazil b Departamento de Cieˆncias Fı´sicas e Matema ´ticas, Universidade Federal de Sa ˜o Paulo, Campus Diadema, Diadema 09972-270, SP Brazil 1. Introduction Biodiesel is the common denomination of the product obtained from the reaction of transesterification of triglycerides, found in vegetable oils or animal fats, with short-chain alcohols. Catalysts are normally used for this reaction, most of which are based on alkaline hydroxides under homogeneous conditions. In the same way, catalytic systems based on acid catalysts such as HCl and H 2 SO 4 have also been reported. However, their use has shown some drawbacks since problems like corrosion and long-time reaction are observed [1]. Due to some advantages the majority of industrial processes are based on heterogeneous catalytic systems. In comparison with homogenous systems, the heterogeneous one allow: (i) easy separation of the catalyst from the reaction medium, resulting in lower product contamination levels; (ii) regeneration and recycling of catalyst; and (iii) to reduce corrosion problems, even if acid species are involved [1]. Indeed, the development of heterogeneous catalytic systems, for biodiesel production, can be an important factor to help the design of continuous processes, thus minimizing separation and purification costs. Nevertheless, in general the use of heterogeneous systems in biodiesel produ- ction provides relatively lower yields [1]. Promising catalysts for biodiesel production via transesterifica- tion reaction are that based on heterogeneous sulfated metal oxides. In fact, these materials have been studied as a potential catalyst for about 20 years for different type of reactions. Hino and Harata have tested the sulfated compounds ZrO 2 and TiO 2 as catalysts in isomerization reactions of n-butane at room tempera- ture [2,3]. Besides, sulfated Fe 2 O 3 and HfO 2 have also been reported as superacids [4]. More recently, sulfated ZrO 2 have been already used in transesterification reaction of vegetable oils, as well as in esterification of the free fatty acids [5–8]. There are different methods to prepare the sulfated metal oxides and the choices of procedures are very important. Also the strategy of the synthetic route employed may lead to materials, exhibiting diverse physical and chemical properties, and conse- quently different catalytic behaviors [9–11]. In general, sulfated metallic oxides can be prepared via impregnation techniques whereby a metallic hydroxide, or oxide, interact with a solution of H 2 SO 4 or (NH 4 ) 2 SO 4 , followed by drying and calcination. In the case of sulfated zirconia (ZrO 2 /SO 4 ), a matrix of ZrO 2 may be prepared from some precursory reagents, like ZrOCl 2 [12], ZrCl 4 [13], ZrO(NO 3 ) 2 [14,15] and Zr(NO 3 ) 4 [16]. One of the first reports on the synthesis of ZrO 2 /SO 4 was presented by Arata [17]. In this work, direct impregnation of sulfate over ZrO 2 , was employed via an aqueous sulfate salt solution. However, Applied Catalysis A: General 347 (2008) 100–105 ARTICLE INFO Article history: Received 29 February 2008 Received in revised form 30 May 2008 Accepted 5 June 2008 Available online 12 June 2008 Keywords: Superacids Biodiesel Transesterification TiO 2 /SO 4 ABSTRACT Superacid sulfated titania catalyst, TiO 2 /SO 4 (TS-series), have been prepared via the sol–gel technique, with different sulfate concentrations. The relation of structure and catalytic activity of the prepared material have been evaluated. The obtained material was characterized by several techniques, as infrared and Raman absorption spectroscopy, pyridine-adsorption infrared spectroscopy, thermogravimetric analyses and obtention of N 2 adsorption–desorption isotherms. The catalyst that exhibits the highest catalytic activity in the methanolysis of soybean and castor oils at 120 8C, for 60 min (40% and 25%, respectively) was that which displayed the highest specific surface area, average pores diameter and pore volume, and highest percentage in sulfate groups (TS-5). ß 2008 Elsevier B.V. All rights reserved. * Corresponding author. Tel.: +55 82 3214 1773; fax: +55 82 3214 1384. E-mail addresses: rusiene@hotmail.com, smpm@qui.ufal.br (R.M. de Almeida). Contents lists available at ScienceDirect Applied Catalysis A: General journal homepage: www.elsevier.com/locate/apcata 0926-860X/$ – see front matter ß 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.apcata.2008.06.006