INOR 233 |
| Gadolinia-doped ceria (GDC) has been frequently used as the ceramic component in the anode cermet materials for solid oxide fuel cells (SOFCs) operating on methane. For methane reactions over high temperature SOFC anodes, especially in the direct-methane SOFCs, carbon deposition (coking) is usually a problem and can cause cell failure; however, the coking problem can be avoided if GDC is used as the anode materials without metal. In these methane reactions, the lattice oxygen of GDC has exhibited important roles. In this work, temperature-programmed reaction of methane and temperature-programmed reduction were performed over gadolinia-doped ceria (GDC). A mechanism of CO and CO2 formations via CH4 reaction over GDC, a mixed ionic-electronic conductor, was derived for the case without gas-phase oxygen, a situation related to direct methane solid oxide fuel cell. It was found that CO2 formation can occur at very much lower temperature than CO formation. The surface lattice oxygen acts as the active site for CH4 adsorption. This active site has a dynamic characteristic due to the mobility of the lattice oxygen. The rates of CO and CO2 formations can be controlled by the supply rate of the lattice oxygen from the GDC bulk; this supply rate depends on the mobility and the concentration of the bulk lattice oxygen. CO2 formation is associated with the surface lattice oxygen while CO formation depends on the O species coming from the bulk lattice. The difference between CO2 and CO formations is only the involvement of the OH species and the O species, respectively, in the final step in their formation mechanism. |
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Inorganic Catalysts
7:00 PM-10:00 PM, Sunday, August 19, 2007 BCEC -- Exhibit Hall - B2, Poster
Division of Inorganic Chemistry |