Mechanism of synthesizing hexaniobate cluster by microwave-assisted hydrothermal reaction
N. Panichakul, H. Nagakari, S. Kikkawa, S. Tsubaki, K. Higashi, T. Uruga, H. Kawasoko, S. Yamazoe
Catal. Today, accepted.
Anionic hexaniobate clusters [Nb6O19]8−, which works as a superbase catalyst, could be synthesized by the microwave-assisted hydrothermal method at 180°C within 10 min with high purity, whereas conventional hydrothermal synthesis method requires a long time reaction time (>24 h). In this study, the mechanism of synthesizing of [Nb6O19]8− by the microwave-assisted hydrothermal method was investigated by in situ quick-scan X-ray absorption fine structure (XAFS) technique and electrospray ionization time-of-flight mass spectroscopy. This revealed that rapid [Nb6O19]8− nucleation along with dissolution of Nb2O5∙nH2O accompanied by the formation of mononuclear Nb species was observed at 160°C. The unveiled mechanistic insights provide the controllability in products during microwave-assisted hydrothermal synthesis of polyoxoniobate clusters.