Lithium ions incorporation in MgO for oxidative dehydrogenation/cracking of propane: Active site characterization and mechanism of regeneration

In the case of Li-promoted MgO two different mechanisms for regeneration of the active site are found when varying the temperature between 550 and 700 °C. Propane titration showed that the active site is deactivated through formation of hydroxyl groups that are stable at 550 °C and below in absence of oxygen. On the contrary at 700 °C, propane pulses resulted in hydrocarbon activation, accompanied by evolution of water molecules. In addition, simultaneous evolution of hydrogen molecules pulsing propane indicate that ODH of propane follows a mixed heterogeneous–homogeneous radical chemistry. No COx was observed while pulsing propane at both temperatures. Moreover COx molecules were not detected even during catalyst regeneration by pulsing oxygen showing that Li/MgO materials are not affected by coke formation. Formation of COx molecules seems to be feasible exclusively by co-feeding propane and oxygen.