Structural Investigation of Mixed Nitrided Galloaluminophosphates "AlGaPON" by EELS, XAS, and XPS Spectroscopies

Amorphous nitrided galloaluminophosphates "AlGaPON" catalysts with nitrogen contents varying from 0 to 23.3 wt% N were obtained by nitriding an Al0.5Ga0.5PO4 precursor under ammonia flow at 750°C in a tubular furnace. The structural changes induced by this treatment were investigated by electron energy loss spectroscopy (EELS), X-ray absorption spectroscopy (XAS), and X-ray photoelecton spectroscopy (XPS). XANES and XPS results indicate that the first-coordination spheres of P, Ga, and Al atoms are modified by nitridation. In particular, the comparison of the P XANES spectra recorded on "AlGaPON" and on a PON phosphorus oxynitride (reference of mixed PO2N2 tetrahedra) reveals that mainly PO2N2 tetrahedra are present in highly nitrided samples. Moreover, the replacement of oxygen by nitrogen probably concerned P–O–Ga bonds rather than P–O–Al. EELS investigation reveals that the precursor is homogeneous at the used probe scale, but indicates that nitridation is accompanied by a loss of homogeneity of the material.