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 degrees C. Propane titration showed that the active site is deactivated through formation of hydroxyl groups that are stable at 550 degrees C and below in absence of oxygen. On the contrary at 700 degrees 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. (C) 2008 Elsevier B.V. All rights reserved.