Morphology-maintaining synthesis of NbN and its catalytic performance in epoxidation

NbN materials have a wide range of applications in the fields of catalysis and semiconductors, due to their unique chemical and physical properties. However, only a few reports focused on the synthesis of NbN materials with different morphologies due to their harsh nitridation conditions. Herein, we successfully prepared amorphous NbN, spherical NbN (NbN-S) and nanobelt NbN (NbN-B) from different niobium precursors with corresponding morphologies by using urea as a nitrogen source at 750 degrees C. Comprehensive characterization (including XRD, N-2 sorption measurements, ICP-AES, FTIR spectroscopy, TG analysis, SEM, TEM, X-ray photoelectron spectroscopy (XPS), and X-ray absorption spectroscopy (XAS)) revealed the formation of NbN and the structural information of these NbN materials. Based on these characterizations, we found that the amount of surface Nb-OH groups is an important factor for successful nitridation under mild conditions. Moreover, the synthesized NbN materials can be used in the epoxidation of cyclooctene and a very high epoxycyclooctane yield (93.9%) was achieved, which is much higher than that over the corresponding Nb2O5 materials. This excellent catalytic performance of NbN materials is supposedly related to the low-coordinated Nb sites and rich vacancies generated during the special nitridation process.