EXAFS study of γ-Mo 2N and Mo nitrides supported on zeolites

Abstract

By analysis of the extended X-ray absorption fine structure (EXAFS) of the Mo K-absorption edge, the structural information of both oxidic and nitrided Mo catalysts supported on zeolites was obtained. The supported MoO 3 samples show three peaks in the radial structure function (RSF). The first two peaks represent the nearest Mo–O coordination shell and the ratio of the first peak to the second one is much larger than that of the MoO 3 crystallites, which suggests that the MoO 3 supported on zeolites has a compact structure than the unsupported one. Three peaks on the RSF of γ-Mo 2N represent one Mo–N and two Mo–Mo coordination shells, respectively. This is in good agreement with the face-centered cubic model. Calculation from X-ray diffraction data and EXAFS spectra reveals that the N atoms in γ-Mo 2N lengthen the distance between Mo atoms and weaken the Mo–Mo bond. Supported Mo 2N samples give out nearly the same RSFs as the γ-Mo 2N and only the peak corresponding to Mo–N shell is weak. This suggests the supported Mo 2N has more configurational disorder.