Identification of the basic sites on nitrided mixed galloaluminophosphates “AlGaPON” catalysts used for the Knoevenagel condensation between benzaldehyde and malononitrile

Abstract

This work deals with the identification of the basic sites on nitrided mixed galloaluminophosphates “AlGaPON”, active in the Knoevenagel condensation between benzaldehyde and malononitrile. The strategy was to compare the properties of five samples, one oxide and four oxynitrides obtained by heating an amorphous Al_0.5Ga_0.5PO₄ precursor under ammonia flow at 750°C for various periods of time. Two acidic molecules, sulfur dioxide and deuterated chloroform were used as IR probes of the basic sites. By comparing the IR spectra recorded before and after adsorption it has been evidenced that the probes interacted specifically with surface –NH₂ groups. It was then concluded that those –NH₂ groups present at the “ AlGaPON” surface were the basic sites responsible for the “AlGaPON” basic catalytic properties. In addition, on untreated oxynitrides, ammonia chemisorbed on Brönsted and for Lewis acid sites influences the course of the Knoevenagel reaction.