Temperature dependence of the pseudomorphic transformation of MoO3 TO γ-Mo2N

The transformation of MoO3 into γ-Mo2N during its nitridation by temperature-programmed reaction with NH3 has been investigated. The X-ray diffraction (XRD) results indicate that the conversion of the MoO3 bulk structure was significant at 673 K, although a notable increase in the surface area was observed at higher temperatures such as 773 K. For the sample synthesized at 973 K for 2 h, the achieved surface area was 140 m2·g−1 with approximately 60% pore volume within the diameter range of 20–30 Å. The XRD and differential thermal analysis (DTA) results indicate that some intermediates, i.e., H0.3MoO3, MoO2, and γ-Mo2OxN1−x, were formed during the pseudomorphic transformation of MoO3 to γ-Mo2N in the temperature range of 673–973 K. Some new information about the transformation reaction was provided by X-ray photoelectron spectroscopy (XPS) and Fourier transformed infrared (FT-IR) spectroscopy. XPS results revealed that Mo2+ species was the main species exposed at the surface of passivated samples.