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

The promoting effect of CeO2 on the catalytic performance of Y2 O3 , which is moderately active catalyst, for the oxidative coupling of methane (OCM) reaction was investigated. The addition of CeO2 into Y2 O3 by coprecipitation method caused a significant increase in not only CH4 conversion but also C2 (C2 H6 /C2 H4 ) selectivity in the OCM reaction. C2 yield at 750 °C was increased from 5.6% on Y2 O3 to 10.2% on 3 mol% CeO2 /Y2 O3 . Further increase in the CeO2 loading caused an increase in non-selective oxidation of CH4 to CO2 . A good correlation between the catalytic activity for the OCM reaction and the amount of H2 consumption for the reduction of surface/subsurface oxygen species in the H2 -TPR profile was observed, suggesting the possibility that highly dispersed CeO2 particles act as catalytically active sites in the OCM reaction. The 16 O/18 O isotopic exchange reaction suggested that the beneficial role of CeO2 in the OCM reaction is to promote the formation of active oxygen species via the simple hetero-exchange mechanism, resulting in the promotion of CH4 activation.