Electrical conductivity of magnesium oxide as a catalyst for radical chain hydrocarbon pyrolysis reactions

The electrical conductivity of polycrystalline MgO between 350 and 750°C is determined by the transport of surface electronic and hole defects and depends on the applied voltage. Near 620°C at low applied voltages, the conductivity decreases by 1–2 orders of magnitude in a narrow temperature range (ΔT = 75°C), and this is accompanied by a change of the sign of the surface charge carriers. The “ignition” of the catalytic activity of magnesium oxide in free radical generation in radical chain hydrocarbon pyrolysis is observed in the same temperature range. It is assumed that the change of the sign of the charge carriers is due to the existence of an isoelectric temperature T i and that, at T > T i , O O · defects come out to the magnesium oxide surface.