ON THE EFFECT OF INTRODUCING ZN2-CAO CATALYST ON ITS SELECTIVITY IN THE OXIDATIVE COUPLING OF METHANE( CATIONS ONTO THE SURFACE OF A NAOH)

ZnO added to a NaOH-CaO catalyst by the incipient wetness method affec ts C-2 hydrocarbon selectivity in the oxidative coupling of methane. T he zinc content was varied between 0.0001 and 1 mol-%. At concentratio ns from 0.0001 to 0.05 mol-% an increase in selectivity was observed a s compared to the undoped catalysts. By X-ray photoelectron spectrosco py analysis of the catalyst surface a negative shift in binding energy of the Zn 2p(3/2) peak in the range of enhanced selectivity was obser ved which is ascribed to an incorporation of zinc cations into the CaO surface lattice. The selectivity increase is supposed to be due to Zn 2+ accepting electrons from CH3- formed by heterolytic splitting of me thane and the subsequent reduction of adsorbed oxygen to O-2 lattice o xygen by electron transfer from Zn1+ or Zn-0.