(392c) In Situ Modification of a Pt Catalyst Supported on a Mixed Ionic-Electronic Conducting Membrane

The electrochemical promotion of a platinum catalyst for ethylene oxidation on a dual chamber membrane reactor was investigated. The catalyst was supported on a La_0.6Sr_0.4Co_0.2Fe_0.8O3 membrane (a known mixed ionic-electronic conductor). Due the supporting membrane's electronic conductivity it is possible to promote the reaction by controlling the oxygen chemical potential difference across the membrane. Upon establishment of an oxygen potential difference across the membrane, oxygen species can migrate and spillover onto the catalyst surface, modifying the catalytic activity. In contrast to classical electrochemical promotion, where the supply of the promoting species is achieved by the application of an overpotential across an ionic conducting membrane, using an external circuit, this system introduces a wireless configuration that is better suited for practical applications. Initial experiments showed an overall promotion of approximately one order of magnitude of the reaction rate of ethylene, under an oxygen atmosphere on the sweep side of the membrane reactor, as compared with the rate under an inert sweep gas. Several parameters such as the oxygen content and flow rate of the sweep gas, the temperature and the duration of the reaction were investigated. In addition, parallels were drawn between classical electrochemical promotion and this new wireless approach. An interesting observation made during these experiments was that the reaction rate could keep its promoted state even after the flow of oxygen on the sweep side was interrupted. This behaviour caused further promotion with every experiment cycle. A possible explanation for this behaviour is that the initial imposition of an oxygen chemical potential across the membrane changes the electrochemical potential difference of the catalyst-support interface on the reaction side. This could in turn change the surface oxygen capture rate on the reaction side. The new rate of surface oxygen capture could be sustained even under a helium sweep maintaining the promotion induced by the initial oxygen sweep. Current work on this system focuses on investigating the causes of permanent promotion and on demonstrating controllable promotion of the catalytic activity.