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 ev olution of different Fe Mo phases, from the fresh precipitate to the a ged and then to the calcined state, has been followed by FT-IR spectro scopy. All the spectral vibrations have been related to different coor dination spheres of Mo and Fe ions in the samples and a comparison wit h a commercial catalyst of similar composition has been made. The new preparation procedure leads to small, uniform (0.3 mum size) particles and a homogeneous morphology of phases as seen by scanning electron m icroscopy. Additionally, a higher surface area (10.3 m2 g-1), lower bu lk density (0.66 g cm-3), a methanol conversion efficiency of > 99% an d an HCHO selectivity of 95% distinguish this sample from the conventi onally prepared one. Better thermal stability of this sample is inferr ed from the IR spectral and XRD analyses of the heat-treated (up to 80 0-degrees-C) samples and is related to the interaction between Fe2(MoO 4)3 and MoO3 phases.