Modification with Amino Groups of Composite SiO2–TiO2 and Pure TiO2 Spheres Prepared via the Peroxo Route.

Abstract

A series of porous composite SiO₂–TiO₂ and pure TiO₂ spherical particles were prepared via the peroxo route and subsequently used as the support for catalyst. Aminopropyltrimethoxysilane (APTMS) was grafted to the surface of support in the strictly unhydrous media leading to bonding of free amino groups to the support surface covalently. Procedure of APTMS grafting is easy to perform and may be spread for grafting other different functional groups to the inorganic surfaces of the catalyst support. The support samples were calcined at various temperatures in order  to optimize the preparation conditions and boost the density of surface amino groups. It has been found that the quantity of grafted APTMS varies insignificantly for the different support samples. Grafted amino groups would be applied as active catalytic sites in different reactions of organic chemistry such as acylation of amines and alcohols, polymerization of  lactones with hydroxyl groups, isomerization of unsaturated compounds, aldol condensation, Diels-Alder, Michael, Knoevenagel  reactions.  The mechanisms of reaction activation by amino groups are the transfer of electron density to a reacting molecule and formation of an intermediate complex. While widely applied catalysts are liquid amines, it is desirable to transform these substances into the heterogeneous form for better regeneration and purification of reaction products from the initial reagents. Prepared catalysts exhibit high amino groups load equal to 1 mmol/g, taking into account the localization of amino groups on the surface of the catalyst.