Partial oxidation of C-2-C-4 alkanes into oxygenates using an Au vertical bar yttria-stabilized zirconia vertical bar Ag electrochemical reaction cell

An electrochemical reactor, using yttria-stabilized zirconia (YSZ) as a solid electrolyte, and gold and silver as the anode and cathode, respectively, has been employed for the selective partial oxidation of alkanes at 425-475 degrees C. Using this system, ethane was converted to acetaldehyde, propane to acetone and acrylaldehyde, butane to methyl ethyl ketone and methyl vinyl ketone, and isobutane to methacrolein. In all cases the combustion products, carbon dioxide and carbon monoxide, were also formed. Alkane oxidation only occurred when the electrical circuit was closed and a current applied across the electrodes; the production rate of the oxygenated products increased as the current, and therefore the oxygen flux across YSZ, was increased. In the presence of only gas-phase dioxygen, oxidation gave carbon oxides. Therefore, it is the electrochemically generated oxygen species that is responsible for the formation of oxygenates from alkanes. It is suggested that the active oxygen species is generated from the 'pumped' oxide ions appearing at the gold/YSZ/gas-phase three-phase boundary. The oxidation of butene to methyl vinyl ketone and crotonaldehyde, and isobutene to methacrolein (and some isobutylene oxide) is also demonstrated.