Amino-grafted metallosilicate MCM-41 materials as basic catalysts for eco-friendly processes

The compounds 3-aminopropyl-trimethoxysilane (APMS), [3-(2-aminoethylamino)propyl]trimethoxysilane (2APMS) and 3-[2-(2-aminoethylamino)ethylamino]propyl-trimethoxysilane (3APMS) were loaded by grafting on MCM-41 matrices of various chemical compositions, aluminosilicate (AlMCM-41; Si/Al = 64) and niobosilicate (NbMCM-41; Si/Nb = 64). The materials prepared were characterized using XRD, N2 adsorption/desorption, thermogravimetric analysis, FTIR spectroscopy and elemental analysis. Thermal stability of APMS was found not to depend on the chemical composition of the support. The higher stability of 2APMS and 3APMS was related to the hydrogen bonding between amine groups and surface hydroxyls. The models of amine grafted in MCM-41 materials were proposed. Basic activity in 2-propanol dehydrogenation and Knoevenagel reactions was found strongly dependent on the nature of the support and changed in the following order: APMS/AlMCM-41 > APMS/NbMCM-41. The acidity of the support is considered for the explanation of the activity sequence.