catalytic behaviour of molybdenum-based zeolitic materials prepared by organic-medium impregnation and sublimation methods

Molybdenum-exchanged zsm-5 catalysts were tested in ethane ammoxidation into acetonitrile at 500 °c and at a very low contact time (0.08 s). the solids were prepared by sublimation, impregnation in ccl4 and solid-state ion exchange methods. the hydration state of the zeolite strongly affected the nature of mocl5 and mo(co)6 decomposition products and, therefore, the concentration of stabilized mo species in the final catalysts. in effect, using dehydrated zsm-5 zeolite, the sublimation of mocl5 led to the most active catalyst (tof = 8.78 s−1) due to the presence, essentially, of [moo4]2− (77%) and [mo2o7]2− (10%) besides less-active crystalline moo3 (12%) and traces of heptamers. however, the impregnation and the solid-state ion exchange of mocl5 as well as the sublimation of mo(co)6 led to less-active catalysts owing to the presence of inefficient moo3 oxide phase. in fact, moderate concentrations of crystalline moo3 should coexist with [moo4]2− species in order to activate c2h6 into c2h4 instead of enhancing the deep hydrocarbons’ oxidation.