In situ XAFS study on Mo Oxide catalysts by molten salt preparation

Preparation of catalysts in molten salt has great possibilities for producing excellent catalysts because the reaction in molten salt is quite different from that in water. MoO3 dissolves in molten salt and finally becomes molybdate via intermediate oxoanions as catalytic active species. The structure of the oxoanions and the mechanism of stabilization on zirconia in the preparation process remain unknown. In the previous study, we have clarified the changes in the composition of molybdate species during the catalyst preparation procedures by quenching the samples. In the present paper, the structure of Mo oxoanions in molten nitrates at different temperatures was investigated by in situ XAFS. Samples were prepared from MoO3 in molten nitrate (NaNO3). The mixture was heated up to various temperatures from 298 to 773 K. The in situ XAFS spectra of the molted samples were measured on Mo K-edge using an in situ cell at the BL-10B in the Photon Factory. The EXAFS was analyzed quantitatively to obtain the structure and composition of Mo oxoanions in the molten nitrates by multi-component fitting based on a linear combination of chi(k) of reference samples and simulation using FEFF8 code in consideration of the Debye-Waller factor. The results show a change of composition of oxoanions in molten nitrate during the reaction.