The Effect of Catalyst Composition on Electric Field-Mediated Catalytic Reactions for Exhaust Emission Control

To prevent global warming, improvements in the efficiency of internal combustion engines and the introduction of hybrid electric vehicles are gaining popularity as ways of controlling carbon dioxide emissions. Because of the lower average temperature of the exhaust gases from these systems, catalytic reactions mediated by an electric field have attracted attention because catalysts can have higher catalytic activity at lower temperatures than conventional catalysts. In addition, they consume less power than electrically heated catalysts. In this study, we determined the catalytic activity of a palladium/ceria-zirconia catalyst in an electric field with exhaust gas temperatures lower than conventional gas temperatures. Further evaluation using catalytic materials with modified ceria-zirconia ratios revealed the importance of the electrical resistance of the materials during electric field–mediated catalytic reactions. Upon modulating the applied current, the current strength was found to be related to a change in the electrical resistance of the catalyst during the reaction. Furthermore, we observed that the activity and electrical resistance of the catalysts were intrinsically linked. These results suggest that electron-promoted surface proton transport and intra-lattice oxygen defects in metal oxide catalysts, as well as their structural changes, significantly contribute to their catalytic activity in an electric field. These electric field–mediated catalytic reactions using modified catalysts can adapt to the growing shift in engine operating conditions by ensuring that the benefits associated with the use of hybrid vehicles and high-efficiency combustion engines are not offset by an increase in the production of carbon monoxide, nitrogen oxide, and unburned hydrocarbons.