Activity and selectivity patterns in the oxidation of allyl iodide on the period IV metal oxides: The participation of lattice oxygen in selective and total oxidation reactions Original Research Article

The oxidation of allyl iodide was studied on the period IV metal oxides with 18O2. In this reaction the selectivity and activity of the period IV metal oxides were determined as a function of temperature. The activity pattern of the allyl iodide oxidation reaction shows the same saw-tooth like pattern as the oxidation of H2 and CH4; i.e. maxima at MnO2, Co3O4 and CuO. However, the differences in activity of the period IV metal oxides in the oxidation of allyl iodide are within one-order of magnitude, which is much smaller than for the oxidation of H2 and CH4. Although in the oxidation of allyl iodide the first step, i.e. abstraction of a hydrogen, is bypassed, the activity is still determined by the average metal–oxygen bond strength: the higher the M–O bond strength the lower the activity. The selectivity pattern looks similar to the activity pattern, only the selectivity pattern varies in anti-phase with the activity pattern: a high M–O bond strength results into a high selectivity to acrolein. The oxidation of allyl iodide with 18O2 and the oxidation of propylene with 18O2 on Co3O4 revealed that the total as well as the selective oxidation products were formed with lattice oxygen from the metal oxide. Reaction of an adsorbed intermediate with gas phase oxygen can only take place if the surface of the oxide is strongly reduced.