REDUCTION AND METATHESIS ACTIVITY OF MOO3/AL2O3 CATALYSTS .2. THE ACTIVATION OF MOO3/AL2O3 CATALYSTS

MoO3/Al2O3 catalysts (0.5-13 wt% MoO3) were activated for the metathesis of propene by thermal treatment in flowing inert gas and by reduction in H2 (reaction conditions: 473 K, 0.1 MPa). Temperatures between 900 and 1140 K were applied for the activation of the catalysts in inert atmosphere. The activity of the supported Mo (molecules s-1 Mo-1) increased with decreasing MoO3 content, which is opposite to the well-known trends for the reducibility of Mo(VI)/Al2O3. The kinetic reaction order of the propene metathesis was found to be 0.8 at 473 K. The apparent activation energy was 30-37 kJ/mole, with a slight decrease at increasing MoO3 content. The response of the activity to the extent of reduction was investigated at different reduction temperatures and MoO3 contents. From these observations and the results of the thermal activation study, it has been concluded that the active sites of metathesis can be formed from both Mo(VI) and Mo(IV) precursors. These precursors coexist on reduced surfaces, while the activity attained after thermal activation in inert gas is due exclusively to sites originating from Mo(VI) species. Other Mo states (Mo(V), Mo(II), and Mo(0)) do not contribute to the metathesis activity. © 1992.