The importance of residual water for the reactivity of MPTMS with silica on the example of SBA-15

The role of water present in the mesopores of SBA-15 on the level of (3-mercaptopropyl)trimethoxysilane (MPTMS) and ((3-aminopropyl)trimethoxysilane (APTMS) for comparison) loading and their stability were studied by experimental and theoretical approaches. N2 ads./des., XRD, XPS, FTIR, thermogravimetry and elemental analyses were used for materials characterization. The results obtained from the periodic DFT calculations and the ab initio molecular dynamics (AIMD) simulations were analyzed to study various possible structures of anchored MPTMS on the surface of SBA-15. Experimental results were very well consistent with theoretical calculations and indicated that the higher the amount of water in SBA-15 the higher the level of modifier loading was obtained. Theoretical calculations allowed the explanation of such feature. The effect of water and modifier concentration in SBA-15 on the oligomerization of MPTMS was considered. The catalytic activity was analyzed in the context of the anchored modifier amount and forms. The H2S release and CC bond formation in the modifier moiety after thermal treatment of the sample in vacuum was analyzed. The effect of water on the efficiency of MPTMS loading on differently hydrated SBA-15 as well as on its forms and properties is presented for the first time, according to our knowledge.