Electric field-induced oxidative coupling of methane over lanthanum and cerium based catalysts

A series of four catalysts, CeO2, CePO4 and LaPO4 in a nanorod structure and CePO4 nanospheres were assessed for the oxidative coupling of methane (OCM) reaction in an electric field at room temperature. The applied current of 3 mA was kept constant throughout the study. The cerium and lanthanum phosphates showed similar and high activity for OCM in the electric field, while CeO2 was not active for OCM reaction, and led only to total oxidation into CO2. C2 selectivity was improved as methane content increased in the feed and reached 27.6 % at a CH4/O2 ratio of 3. Switching the polarity of the current from positive to negative shifted the C2 selectivities to acetylene (18.2 %) for CePO4. It was suggested that this shift was related to the deposited power due to the polarity switch rather than the polarity effect on the electric field. Changing the structure of the CePO4 catalyst from nanorod to nanosphere did not alter the conversion or selectivities, indicating that the morphology does not compromise the reactivity.