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A series of bifunctional heterogeneous catalysts based on SBA-15 supports modified with Zr, Nb and Mo species functionalized by aminopropyl siliceous species has been used in the Knoevenagel condensation. The results indicated that the acid–base synergetic effects of the centres present on these catalysts seem to have significant effect on the Knoevenagel condensation of benzaldehyde with active methylene compounds. Basic sites and Lewis acid sites play different roles depending on the methylene compound used in the Knoevenagel condensation. Depending on the chemical composition of the catalysts, the reaction can proceed on basic sites exclusively or on the pairs of acidic-basic centres. The nature of metal species strongly influences the activity in the Knoevenagel condensations but does not affect the selectivity. [ABSTRACT FROM AUTHOR]

Transition metals of group IV (Zr), group V (Nb), and group VI (Mo) were introduced into SBA-15 materials during the synthesis towards the production of metallosilicates, MSBA-15, to be used as supports for 3-aminopropyl-trimethoxysilane (APTMS), and 3-[2-(2-aminoethylamino)ethylamino]propyl-trimethoxysilane (3APTMS). The materials obtained were characterized by N 2 adsorption/desorption, XRD, TEM, ICP, XPS, UV-Vis, FT-IR and pyridine adsorption. The results indicated that the metals were loaded in the cationic state: Zr 4+ , Nb 5+ and Mo 6+ and preferentially located on the SBA-15 surface. The highest efficiency of metal loading in SBA-15 under the conditions used in this work was reached for molybdenum, whereas the highest metal content on the surface was observed for ZrS. The number of Lewis acid sites (LAS) changed in the following order: ZrS⪢; NbS > MoS, whereas their strength as follows: ZrS > NbS > MoS(HP). Zirconium containing material exhibited additionally BrØnsted acidity. The efficiency of propyl-amine incorporation changed according to the electron state of metals: Zr Nb Mo. The binding of propyl-amine to metal cations determined the amine stability. [ABSTRACT FROM AUTHOR]