Control of amine functionality distribution in polyvinylamine/SBA-15 hybrid catalysts for Knoevenagel condensation

• Poly(N-vinylformamide) can be deposited on SBA-15 surface by in situ polymerization.
• Acid-catalyzed hydrolysis transforms surface amide groups into amine ones.
• Distribution of N-containing species is controlled by neutralization at different pH.
• NH2 species deposited on SBA-15 are active sites in Knoevenagel condensation.
• The best results are achieved for reaction involving methylene compound with low pKa.

Poly(N-vinylformamide) was deposited on the surface of highly ordered hexagonal mesoporous silica SBA-15 by in situ polymerization. Acid-catalyzed hydrolysis followed by neutralization with NaOH (pH = 7.0–10.0) allowed obtaining the poly(vinylamine)/SBA-15 hybrid materials with various distributions of N-containing species, which were determined by XPS and DRIFT spectroscopy. The changes in the form of deposited polymer as well as its interaction with the silica support were discussed. The poly(vinylamine)/SBA-15 materials were tested as catalysts of Knoevenagel condensation of benzaldehyde with ethyl cyanoacetate, ethyl acetoacetate and diethyl malonate. It was found that the sample neutralized at pH = 9.0 showed the best catalytic performance, which was attributed to a high content of accessible NH2 groups.

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