Calcination of the MCM-41 mesophase: mechanism of surfactant thermal degradation and evolution of the porosity

Sample controlled thermal analysis (SCTA) has been used to carefully and re producibly eliminate the organic surfactant template from pure silica mesop orous MCM-41. The reproducibility allowed a number of intermediate species to be isolated permitting complementary measurements. To understand the mec hanisms by which the surfactant is removed, evolved gas analysis as well as H-1 and C-13 MAS NMR were used. The liberation of the porosity and evoluti on of the surface hydrophobicity were followed by gas adsorption, XRD and i mmersion microcalorimetry. It would seem that two types of cetyltrimethylammonium surfactant exist in the confined state, of which the large majority decomposes at a lower tempe rature (up to 200 degrees C) within the silica organic host than in the pur e state. A small quantity of organic fragments are still observed within th e pore structure up to 500 degrees C. Gas adsorption shows a pore blocking effect occurs during the surfactant removal.