FT-IR studies on the evolution of different phases and their interaction in ferric molybdate-molybdenum trioxide catalysts

Two samples of Fe–Mo catalysts have been prepared from ferric nitrate and ammonium paramolybdate, one following a conventional procedure and the other by a new precipitation procedure in a buffer medium. The evolution of different Fe–Mo phases, from the fresh precipitate to the aged and then to the calcined state, has been followed by FT‐IR spectroscopy. All the spectral vibrations have been related to different coordination spheres of Mo and Fe ions in the samples and a comparison with a commercial catalyst of similar composition has been made. The new preparation procedure leads to small, uniform (0·3 μm size) particles and a homogeneous morphology of phases as seen by scanning electron microscopy. Additionally, a higher surface area (10·3 m 2 g −1 ), lower bulk density (0·66 g cm −3 ), a methanol conversion efficiency of > 90% and an HCHO selectivity of 95% distinguish this sample from the conventionally prepared one. Better thermal stability of this sample is inferred from the IR spectral and XRD analyses of the heat‐treated (up to 800°C) samples and is related to the interaction between Fe 2 (MoO 4 ) 3 and MoO 3 phases.