06 Electrical power supply and utilization (scientific, technical)
00/03392
Isolation of oxygen-formed during catalytic reduction of carbon dioxide using a solid electrolyte membrane Furukawa, S. er al. Energy Fuels, 1999, 13, (5), 10741081. The separative recovery of oxygen formed during the hydrogenation of carbon dioxide was studied using a composite system consisting of yttriastabilized zirconia (YSZ) membrane-equipped silver electrodes as a pump and a nickehzeolite catalyst to initiate the hydrogenation of carbon dioxide. The methanation of carbon dioxide proceeded efficiently in the presence of the nickei/zeolite catalyst even at 873 K, the lowest functional temperature at which YSZ has ionic conductivity.
Carbon dioxide conversion and methane yield reached 100% and SO%, respectively, at Ha/CO2 = 10, space velocity c 6200 h-', and 873 K. Carbon dioxide was adsorbed by the crystal structure of the zeolite even at 873 K, and methanation of the adsorbed carbon dioxide (CO2 ad) proceeded by the following one-step reaction: COsad + 3Hz -+ CHI + HaO. The rate constant of methanation was estimated to be 1.6 x lo-* cm' g-cat-t s-i for the pseudo-first-order reaction. Electrochemical isolation of oxygen formed during hydrogenation of carbon dioxide was carried out under galvanostatic conditions. It was assumed that the oxygen was converted to water by the nickehzeolite catalyst and then transported through the YSZ electrolyte after the water was ionized. It was assumed that the oxygen was not formed by the dissociation of carbon dioxide directly on the cathode electrode. It appeared that the rate-determining step for isolation of oxygen on the cathode electrode in the presence of the nickelizeolite catalyst was the charge transfer process.