Thermal decomposition of ammonium molybdate for MoO3 preparation: temperature effects and structural evolution mechanism

The thermal decomposition of ammonium molybdate is a key step in the preparation of MoO 3 , however, the decomposition pathway, intermediate evolution, and temperature dependent structural transformation during this process remain insufficiently understood. In this study, the thermal decomposition behavior of ammonium molybdate under different temperature conditions, with particular emphasis on the influence of decomposition temperature on the physicochemical properties of the products and the underlying decomposition mechanism at multiple scales. Phase composition, crystal structure, and microstructure were characterized by XRD and SEM; laser particle sizing and BET surface area analysis revealed temperature-dependent evolution of particle size and surface area, identifying the critical temperature range for complete decomposition. Combined FT-IR, TG-DSC, and TG-MS analyses reveal the disappearance of ammonium species, reconstruction of the Mo-O framework, and the evolution characteristics of gaseous products. At the molecular level, DFT calculations were performed to optimize the molecular structure and analyze bond orders, clarifying the relative stability and cleavage sequence of key chemical bonds during decomposition. Furthermore, reactive molecular dynamics simulations based on the ReaxFF force field were conducted using LAMMPS to dynamically capture bond-breaking and bond-forming processes involving N-H and Mo-O bonds under thermal activation. The combined experimental observations, theoretical calculations, and dynamic simulations provide a multiscale understanding of the thermal decomposition mechanism of ammonium molybdate, offering detailed insights into the decomposition pathway, intermediate evolution, and bond-breaking processes. These findings offer mechanistic guidance for the controlled preparation of molybdenum oxide materials and a useful reference for the thermal decomposition of other metal ammonium salts.