OXIDATIVE COUPLING OF CH4 ON AG CATALYST-ELECTRODES DEPOSITED ON ZRO2 (8 MOL-PERCENT-Y2O3)

The oxidative coupling of CH4 was investigated on polycrystalline Ag films deposited on yttriastabilized zirconia (YSZ) at temperatures 720 to 850°C. It was found that electrochemical supply or removal of O2- to or from the catalyst film results in very significant changes in both the rate of CH4 consumption and in the product selectivity. For high CH4-to-oxygen ratios, electrochemical supply of O2- causes up to 50-fold increases in the rate of CH4 consumption with a concomitant decrease in C2 hydrocarbon selectivity. Electrochemical removal of O2- causes a decrease in the rate of CH4 consumption and an increase in C2 selectivity. Electrochemically supplied oxygen can be significantly more active and selective than gas-phase oxygen. By varying the imposed current and catalyst potential the selectivity to C2 hydrocarbons is varied reversibly between 25 and 75%. Maximum C2 hydrocarbon yield was 8%. Due to the high operating temperatures, direct electrocatalysis and homogeneous reactions, more than NEMCA, affect the overall kinetic behaviour. © 1993 Academic Press, Inc.