The radical species and impurities present in mesoporous silicas as oxidation active centres

Three kinds of mesoporous silicas with hexagonal arrangement of mesopores, i.e. MCM-41, SBA-3 and SBA-15, were synthesised and characterised by XRD, N2 adsorption, FTIR, UV–vis and ESR techniques. A choice of these silicas was determined by the use of various siliceous precursors, templates and synthesis conditions. Their catalytic activity was estimated in the oxidation of methanol (gas phase) and cyclohexene (liquid phase) as well as in acid-basic test reactions (propanol–2 decomposition and acetonylacetone (AcAc) cyclisation). It was evidenced that the sources of siliceous, nature of templates and the preparation conditions (pH) play a crucial role in the formation of active species. The E′ and NBOHC (Si–O) and iron and chloride impurities were estimated as active centres for both oxidation reactions.