Investigation of Heterogeneous Catalysts by an Electrochemical Method: Ceria and Titania-Supported Iridium Nanoparticles for Ethylene Oxidation

Abstract

Recently, metal support interaction (MSI) has been demonstrated to be closely related to electrochemical promotion of catalysis (EPOC) in the functionality of the process through spillover/backspillover of ionic species to/from the conductive support. In the present work, the interaction that iridium oxide (IrO x ) nanoparticles have with two mixed ionic-electronic conducting (MIEC) materials (i.e., ceria, CeO 2 and titania, TiO 2 ) for ethylene oxidation is evaluated. To this end, the open circuit catalytic oxidation of ethylene as well as steady-state polarization measurements were carried out for free-standing (unsupported) IrO x and ceria- and titania-supported IrO x (~1 nm). The presence of these two supports was found to increase the catalytic reaction rate when compared to the free-standing IrO x , and decrease the electrochemical reaction rate at the three-phase boundary, as confirmed by the exchange current density (i 0 ). In the light-off experiments, the IrO x /CeO 2 catalyst showed a higher reaction rate until 300 0 C; however IrO x /TiO 2 was superior at 350 0 C. It was also shown that the catalysts with lower i 0 resulted in higher open-circuit reaction rates due to the larger amount of thermally-induced backspillover promoters to the gas exposed catalyst surface, in agreement with the EPOC phenomenon.