DRIFTS study of the surface structure and nitridation process of mixed galloaluminophosphate oxynitride (AlGaPON) catalysts

The spectra of high surface area amorphous oxide AlPO, AlGaPO, and GaPO were compared with those of high surface amorphous oxynitrides AlPON and AlGaPON with similar O/N ratio and with that of the nitride GaN. This allowed us to make a correct assignation of the bands in their IR vibrational spectra, especially those in the new family of solids named galloaluminophosphate oxynitride, AlGaPON. The substitution of aluminum atoms by gallium induces a shift of the framework band vibrations due to a second-neighbor effect. The introduction of nitrogen in the network of the oxide phosphate produces a broadening and poor definition of the structural bands due to a collapse of the structure. NH4+, coordinated NH3, -NH2, and -NH- species are identified on the surface of the AlGaPON solid. A thermal treatment under NH3 allows us to propose the following nitridation sequence: M-O-NH4+ and/or M-NH3 --> M-NH2 --> M-NH-M --> N3-.