Promoting Effect of Cerium Oxide on the Catalytic Performance of Yttrium Oxide for Oxidative Coupling of Methane

The promoting effect of CeO(2) on the catalytic performance of Y(2)O(3), which is moderately active catalyst, for the oxidative coupling of methane (OCM) reaction was investigated. The addition of CeO(2) into Y(2)O(3) by coprecipitation method caused a significant increase in not only CH(4) conversion but also C(2) (C(2)H(6)/C(2)H(4)) selectivity in the OCM reaction. C(2) yield at 750 °C was increased from 5.6% on Y(2)O(3) to 10.2% on 3 mol% CeO(2)/Y(2)O(3). Further increase in the CeO(2) loading caused an increase in non-selective oxidation of CH(4) to CO(2). A good correlation between the catalytic activity for the OCM reaction and the amount of H(2) consumption for the reduction of surface/subsurface oxygen species in the H(2)-TPR profile was observed, suggesting the possibility that highly dispersed CeO(2) particles act as catalytically active sites in the OCM reaction. The (16)O/(18)O isotopic exchange reaction suggested that the beneficial role of CeO(2) in the OCM reaction is to promote the formation of active oxygen species via the simple hetero-exchange mechanism, resulting in the promotion of CH(4) activation.