Abstract
Reproducible data of surface DC conductivity of various MgO catalysts were obtained at the temperature of 673 to 1173K. As has been well known, Li + /MgO is a selective catalyst of the oxidative coupling of methane (OCM), while MgO and especially Zr 4+ /MgO give poor C 2 hydrocarbon-selectivity in OCM reaction. The effects of gaseous oxygen on the conductivity at the OCM reaction temperature (873 to 1073K) were positive, null and negative for Li + /MgO, MgO, and Zr 4+ /MgO, respectively. The first case is related with the p-type conductivity. Hole located on the lattice oxygen means O” anion radical, which is believed to be one of the active species in the OCM reaction. So the conductivity measurement is discussed in connection with the active species measurement. Water also influenced the DC conductivity especially at the low temperature. Deuterium isotope effects were observed at the low temperature for all the MgO catalysts. The defects generated by water inclusion was also discussed in connection with the active center formation.
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