Studies on [Li+O-] centers in oxidation-dehydrogenation of ethane to ethene on Li+/MgO catalysts

In this paper, the formation mechanism and characterization of [Li+O-] centers on Li+/MgO are investigated by the reaction of oxidation-dehydrogenation of ethane to ethene. The concentration of the centers increases with disappearance of free hydroxyl groups in Li+/MgO. The Li+ entering defect of cations reacts with free hydroxyl to form [Li+O-], for which the mechanism is as follows: [GRAPHICS] 2Li(+)OH(-) (Delta)--> Li2O + H2O 2Li(2)O + O-2(ad) --> 4Li(+)O(-) They have a positive heat of formation, thus, the concentration of the centers increases with increasing temperature. The process of forming [Li+O-] needs to expend surface oxygen, thus, suitable O-2(g) is necessary according to the balance of oxygen species over the catalysts, but excessive O-2(g) is harmful. The defect of lower coordination numbers affects the formation of [Li+O-], because it affects the existent state of surface Li+.