Introduction The synthesis and properties of highly ordered meso- porous materials M41S were reported by the Mobil scientists fifteen years ago [1, 2]. The silica based MCM-41 as a member of this family of the materials attracted most attention due to its hexagonal array of uniform pores, the high surface area and high total pore volume. Although the structural properties of these mesoporous solids as well as various routes of their synthesis were extensively investigated over the last years, the processes inside the pores at subse- quent stages of the preparation procedure are still un- der discussion. The surfactant transformations against the temperature during calcination are well recog- nized up to ~250°C. Above this temperature in the ox- idizing atmosphere the chemical species present in- side pores are transformed into carbon dioxide and water. The thermal decomposition of the surfactant template (CTAB) was studied in detail using the TPD technique [3–6]. High temperature treatment of as- synthesized MCM-41 changes additionally the con- centration of the surface hydroxyls, which decreases upon calcination [7, 8]. The most commonly method used to remove the template is the calcination in air. After calcination on the silica surface remain hardly removable carbon deposits or coke [9–11]. The mechanism of the surfactant decomposition during calcination has a step-character as described by Kleitz et al. [12, 13]. They suggested that below 250°C 46% of the template is removed by hexadecene evaporation resulting from the Hoffman degradation and elimination of trimethylamine. Both compounds were reported earlier by Beck et al. [2] and Keene et al. [14] for MCM-41 templated by hexa- decyltrimethylammonium chloride. At a relatively low temperature 250–300°C fragmentation of the alkyl chain takes also place producing shorter hydro- carbons [15, 16]. Recently Kumar et al. [17] carried out 13 C CPMAS NMR studies of the thermal decomposi- tion of the template CTAB at 200°C. They stated the presence of N,N-dimethylhexadecylamine CH 3 (CH 2 ) 15 N(CH 3 ) 2 as a product of CTAB decompo- sition in MCM-41 surroundings. In our previous paper [18] we demonstrated the presence of 1-hexadecene and N,N-dimethylhexa- decylamine in the liquid residue that condensed at the outlet of the chromatographic column containing MCM-41 sample heated up to 250°C in hydrogen flow. Under these conditions we obtained MCM-41 silica synthesized by CTAB as a template possessing emptied pores and structural parameters similar to those of the calcined sample. Moreover, most of the surface silanols were preserved, and their concentra- tion was much higher than for the calcined sample. In the present paper the results of similar experi- ments for silica and silica–aluminium of the MCM-41 type are reported. The aim of this study was to give some information on the chemical processes involved in the surfactant removal in non-oxidizing atmosphere. An additional aim of the present paper was to test how aluminium incorporated into the framework of MCM-41 mesoporous materials influences the re- 1388–6150/$20.00 Akadémiai Kiadó, Budapest, Hungary © 2009 Akadémiai Kiadó, Budapest Springer, Dordrecht, The Netherlands THERMAL DEGRADATION OF CTAB IN AS-SYNTHESIZED MCM-41 J. Goworek 1* , Agnieszka Kierys 1 , W. Gac 2 , Anna Borówka 1 and R. Kusak 1 1 Department of Adsorption, Faculty of Chemistry, Maria Curie-Sk Óodowska University, Pl. M. Curie-SkÓodowskiej 3 20-031 Lublin, Poland 2 Department of Chemical Technology, Faculty of Chemistry, Maria Curie-Sk Óodowska University, Pl. M. Curie-SkÓodowskiej 3 20-031 Lublin, Poland Thermal evacuation of a surfactant template from pure siliceous MCM-41 and MCM-41 containing aluminium in hydrogen flow was investigated. Micelle templated MCM-41 were prepared using hexadecyltrimethylammonium bromide (CTAB). The products of thermal surfactant degradation outside and inside pores were identified at various temperatures using 13 C solid-state nuclear mag- netic resonance (NMR) spectroscopy, gas chromatography coupled with mass spectrometer (GC-MS) and temperature programmed desorption coupled with mass spectrometer (TPD-MS). The GC-MS and 13 C MAS NMR results obtained from this study provide an insight into the mechanism of surfactant transformation during MCM-41 synthesis on molecular level. Keywords: CTAB, GC-MS, MAS NMR, MCM-41, template removal * Author for correspondence: jgoworek@hermes.umcs.lublin.pl Journal of Thermal Analysis and Calorimetry, Vol. 96 (2009) 2, 375–382