Nitrogen incorporation in an Al0.5Ga0.5PO4 amorphous solid studied with Al-27 and P-31 NMR

Amorphous nitrided galloaluminophosphate "AlGaPON" catalysts with nitrogen contents varying from 0 to 23.3 wt % were obtained by nitriding an Al0.5Ga0.5PO4 precursor under ammonia flow at 750 degreesC in a tubular furnace. Because these AlGaPON catalysts present very promising properties to the field of acid-base catalysis, an attempt was made to describe the structural changes induced by nitrogen incorporation in their structure so as to link their catalytic properties to their short-range structure. In this paper, we compare results previously obtained using X-ray absorption spectroscopy (XAS) and X-ray photoelectrons spectroscopy (XPS) on a series of five samples with increasing nitrogen content with new P-31 MAS NMR, Al-27 MAS, and Al-27 MQ(3Q) MAS results obtained on the same samples. P-31 NMR results confirmed our previous model, which indicated the formation Of PO3N units at the beginning of nitridation, followed by the apparition Of PO2N2 units in the highly nitrided samples. Al-27 NMR results allow us to propose the subtitution of oxygen atoms by nitrogen atoms in the first coordination sphere of aluminum, a result that is different from what is observed in nitrided aluminophosphates "AlPON". This last result is further evidence of the particular influence of gallium atoms in the nitridation process.