Surface Conductivity Measurement of Catalyst Materials by EUPS and Its Correlation to Catalyst Performance

Commercial three way catalysts (TWC) are designed to eliminate HC, CO and NOx pollutants emitted from gasoline powered internal combustion engines. TWC have been optimized over many years to meet ever more stringent emission regulations. It has long been speculated that surface electrical conductivity may be a key parameter in controlling catalytic activity, however until now it has not been possible to reliably measure this physical parameter on a catalytic surface.

In this study, the surface electrical conductivity of catalyst powders, such as Rh/ CeO_1-x-Zr_xO₂, Rh/ZrO₂ and Rh/Al₂O₃, were measured by EUPS (Extreme Ultraviolet excited Photoelectron Spectroscopy). Then the measured electrical conductivity was compared with catalyst performance from CO-NO and water gas shift reactions which are important for controlling automobile exhaust emissions from gasoline vehicles. Good correlation was observed between the surface electrical conductivity and catalytic light-off performance for both reactions, thus linking the contribution of the surface electrical conductivity to catalytic activity.