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

This work deals with the identification of the basic sites on nitrided mixe d galloaluminophosphates "AlGaPON", active in the Knoevenagel condensation between benzaldehyde and malononitrile. The strategy was to compare the pro perties of five samples, one oxide and four oxynitrides obtained by heating an amorphous Al0.5Ga0.5PO4 precursor under ammonia flow at 750 degrees C f or various periods of time. Two acidic molecules, sulfur dioxide and deuter ated 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 c oncluded that those -NH2 groups present at the "AlGaPON" surface were the b asic sites responsible for the "AlGaPON" basic catalytic properties. In add ition, on untreated oxynitrides, ammonia chemisorbed on Bronsted and for Le wis acid sites influences the course of the Knoevenagel reaction.