Functionalised SH-MCM-41 materials have been prepared via grafting and co-condensation. A detailed thermogravimetric-mass spectrometry (TG-MS) study of SH-MCM-41 and the correspondent acid form SO3H-MCM-41 materials has been carried out. The influence of the oxidation procedure in the final sulphur species is described. It has been demonstrated that the use of concentrated H2O2 optimises the oxidation process and minimises the formation of intermediate species not active in acid catalysed reactions. (C) 2003 Elsevier B.V. All rights reserved.