High Turnover Frequency CO–NO Reactions over Rh Overlayer Catalysts: A Comparative Study Using Rh Nanoparticles

A comparative turnover frequency (TOF) study for structure-sensitive CO–NO reactions between overlayer (thin-film) and nanoparticle Rh catalysts was performed using a combined experimental and theoretical approach. Two types of honeycomb catalysts were prepared: one by the arc-plasma deposition of a 3 nm Rh overlayer having a (111) preferential orientation atop a 20-μm Fe–Cr–Al metal foil and the other by a conventional wet coating of Rh/ZrO2 powders comprised of Rh nanoparticles onto a cordierite honeycomb. The reaction rate of the overlayer was found to be more superior to the nanoparticles, despite a smaller surface area, as the TOF was 14-fold greater on the overlayer than on the nanoparticle. In situ infrared spectroscopy suggested that a hollow-site NO formed onto the overlayer in contrast to the bridge- and on-top-NO adsorptions on the nanoparticles. The energy barriers for surface reactions of adsorbed NO molecules were analyzed using a density functional theory based molecular dynamics approach f...