Thermochimica Acta 443 (2006) 183–188 Kinetic parameters of surfactant remotion occluded in the pores of the AlMCM-41 nanostructured materials Marcelo J.B. Souza a , Antonio S. Araujo b,∗ , Anne M.G. Pedrosa b , Stevie H. Lima b , Valter J. Fernande Jr. b a Department of Chemical Engineering, Federal University of Sergipe, 49100-000 S˜ ao Cristov˜ ao, Sergipe, Brazil b Department of Chemistry, Federal University of Rio Grande do Norte, CP1662, 59078-970 Natal, RN, Brazil Received 19 September 2005; received in revised form 20 December 2005; accepted 24 December 2005 Available online 21 February 2006 Abstract A series of AlMCM-41 molecular sieves was synthesized starting from a hydrogel with the following molar composition: 1CTMABr: 4.58SiO 2 :(0.437 + X)Na 2 O:XAl 2 O 3 :200H 2 O. Tetramethylammonium silicate (TMAS) was used as silicon source and cethyltrimethylammonium bromide (CTMABr) was used as structure template. The obtained materials were characterized by nitrogen adsorption, XRD, FT-IR and TG/DTG. Model-free kinetic algorithms were applied in order to determinate conversion, isoconversion and apparent activation energy to decomposition of CTMA+ species from the AlMCM-41 materials with different silicon/aluminium (Si/Al) ratios of 20, 40, 60 and 80. © 2006 Elsevier B.V. All rights reserved. Keywords: AlMCM-41; Si/Al ratio; CTMA+; Model-free kinetics 1. Introduction Silica-based M41S materials discovered by Mobil Company in the early 90s [1,2] are very interesting class of mesoporous materials. MCM-41 (p6mm) silica whose pore structure con- sists of hexagonally packed cylindrical is the main component of the M41S family. Hexagonal mesoporous systems with high surface area open possibilities of generate the surface acidity necessary to catalyze organic reactions as transesterification of vegetable oils producing biodiesel [3,4]. The formation of the AlMCM-41 phase occurs according to the liquid crystal tem- plate (LCT) mechanism, in which tetrahedral SiO 4 and AlO 4 species react with the surfactant template under hydrothermal conditions [5]. A typical preparation of AlMCM-41 needs basi- cally of a solvent, a template (surfactant molecule), a silica source and an aluminium source [6–8]. In order to be used as adsorbents and catalytic applications the MCM-41 mate- rials need to pass for a process for removal of the template molecules in the pores. Some works were published studying the removal of those template molecules, of which they are more ∗ Corresponding author. Tel.: +55 84 2119240; fax: +55 84 2119240. E-mail address: asa-ufrn@usa.net (A.S. Araujo). mentioned: extraction by solvents, extraction with CO 2 and cal- cination [9–11]. In most of the cases authors give significant importance to the calcination for showing more efficiency and to guarantee the complete removal of CTMA+ and AlMCM-41 materials with several silicon/aluminium atomic ratios (Si/Al). The variables in a typical calcination process are time, tempera- ture, heating rate, catalyst mass and dynamic atmosphere. In this work, thermogravimetry is used for studying the kinetic param- eters of CTMA+ removal employing integral TG curves and a model-free kinetic method [12–14] to calculate the activation energy, the conversion rates and the isoconversion parameters to evaluate the stage of decomposition of removal template species as function of temperature and time under dynamic flow conditions. 2. Experimental The AlMCM-41 materials were synthesized starting from tetramethylammonium silicate solution (TMAS, Sigma– Aldrich, P A = 17.5%) as silicon source, sodium hydroxide (VETEC, P B = 99%) as sodium source, pseudobohemite (Vista, P C = 70%) as aluminium source, cethyltrimethylammonium bromide (CTMABr, VETEC, P D = 98%) as structural template and distilled water as solvent. For the pH adjustment, 30% acetic 0040-6031/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.tca.2005.12.022