SYNTHESIS GAS-PRODUCTION IN METHANE CONVERSION USING THE PD-VERTICAL-BAR-YTTRIA-STABILIZED ZIRCONIA AG ELECTROCHEMICAL MEMBRANE SYSTEM

The electrochemical membrane reactor of YSZ (yttria-stabilized zirconi a) solid electrolyte coated with Pd and Ag as anode and cathode, respe ctively, has been applied to the partial oxidation of methane to synth esis gas (CO + H-2). The Pd\YSZ\Ag catalytic system has shown a remark able activity for CO production at 773 K, and the selectivity to CO wa s quite high (96.3%) under oxygen pumping condition at 5 mA. The H-2 p roduction strongly depended on the oxidation state of the Pd anode sur face. Namely, the H-2 treatment of the Pd anode at 773 K for 1 h drast ically reduced the rate of H-2 production, while air treatment enhance d the H-2 production rate. From the results of the partial oxidation o f CH4 with molecular oxygen, it is considered that the reaction site o f the electrochemical oxidation of CH4 to synthesis gas was the Pd-YSZ -gas-phase boundary (triple-phase boundary). In addition, it is found that the oxygen species pumped electrochemically over the Pd surface d emonstrated similar activity to adsorbed oxygen over Pd, PdOad, for th e selective oxidation of CH4 to CO, when the Pd supported on YSZ was u sed as a fixed-bed catalyst for CH4 oxidation with the adsorbed oxygen . The difference with respect to the Hz formation between the electroc hemical membrane system and the fixed-bed catalyst reactor results fro m differences in the average particle size of Pd and the way of the ox ygen supply to the Pd surface.