ALKENE OXIDATION OVER THE AU/YTTRIA-STABILIZED ZIRCONIA/AG SYSTEM

An electrochemical reactor using yttria-stabilized zirconia (YSZ) as a solid electrolyte and gold and silver as anode and cathode metals, respectively, (i.e. alkene,Au\YSZ\Ag,O2) has been used for alkene oxidation. Despite the inertness of the gold anode in the dissociative activation of molecular oxygen, partial oxidation of alkene to the corresponding oxygenated compounds, i.e. ethene to acetaldehyde, propene to acrylaldehyde and but-1-ene to both methyl vinyl ketone and crotonaldehyde, have been observed together with complete oxidation over the gold anode under oxygen pumping. The production rate of the oxygenated products increased with increasing oxygen pumping through YSZ at 723-748 K. No production of the oxygenated product has been observed for both propene and but-1-ene oxidations under open-circuit conditions, i.e. no oxygen pumping, while ethene was oxidized to acetaldehyde in both the presence and absence of gaseous oxygen. It is considered that oxide ions can be partially reoxidized at the three-phase boundary of Au/YSZ/atmosphere on the anode surface to form an active oxygen species which can oxidize the alkenes to the oxygenated compounds. This is the first evidence that can clarify the activity of oxygen species from oxide, i.e. lattice oxygen species in YSZ.