Crystallochemical transformations at low temperature reduction of molybdenum trioxide

Presented are the results of investigations of structural and phase transformations occurring in low-temperature (200-500 deg C) reduction of molybdenum trioxide crystals activated by coating with a thin layer of palladium. It is found that their reduction begins at a temperature by 100-150 deg C lower than that of pure crystals and involves initially a characteristic disintegration not related to the MoO3-MoO2 change-over. It is shown that the reduction on the thin layer of molybdenum trioxide directly contacting palladium proceeds in a manner omitting the MoO3→MoO2 change-over and is characterized by the formation of an intermediate molybdenum suboxide having a NaCl-type stucture and a=4.08 A. Discussed are the regularities of the change-over of the MoO3 crystal to that of the suboxide. Experiments have demonstrated that it is precisely this change-over which is responsible for the disintegration of the initial crystal on the initial stage of the reduction. Further reduction of the disintegrated crystal follows the usual scheme of MoO3→MoO2→Mo