The effect of NO and CO on the Rh(100) surface at room temperature and atmospheric pressure

Rhodium is used in automotive catalysis to reduce NO and CO emission by catalyzing the reduction of NO to N2 and the oxidation of CO to CO2. Rhodium nanoparticles in the catalyst are exposed to high pressures of NO and CO, which leads to disintegration and sintering of the catalyst. To design more stable catalysts, the effects of high pressures of NO and CO on rhodium must be understood. Therefore, we studied the Rh(100) surface, which is most active for NO reduction by CO, at atmospheric pressures of NO and CO with scanning tunneling microscopy. Atomistic thermodynamics, low-energy electron diffraction, and Auger electron spectroscopy were used to understand the behavior of adsorbates on the surface. We observe the formation of rhodium islands and roughening of the step edges at high CO pressures. Roughening does not occur at the same pressures of NO, and is also less severe when co-dosing NO and CO, even at identical CO partial pressures. Atomistic thermodynamics shows that NO likely inhibits CO adsorption by blocking adsorption sites, preventing carbonyl formation, and decreasing surface roughening. [Display omitted] •Exposure of Rh(100) at atmospheric pressures of CO at room temperature causes significant roughening of terraces and steps.•Exposure of Rh(100) at atmospheric pressures of NO at room temperature does not cause significant roughening but molecular adsorption of NO.•Exposure of Rh(100) at atmospheric pressures of CO and NO results in molecular NO adsorption that blocks CO adsorption.•The observed effects of CO and NO on Rh(100) show opposite behavior compared to Rh nanoparticles.