Experimental and Computational Studies of CO and NO Adsorption Properties on Rh-Based Single Nanosized Catalysts

In this work, we investigated the mechanisms for the high activity and durability of Rh single nanosized catalysts for the CO–NO reaction in three-way catalysis. For this, we analyzed the relationship between the Rh particle morphology and surface adsorption of CO and NO molecules on Rh via transmission electron microscopy, in situ Fourier transform infrared (FT-IR) spectroscopy, and density functional theory calculations. Compared with that of the Rh-loaded catalyst as a conventional catalyst, we clearly found differences in the size of the Rh nanoparticles supported on the oxides. Additionally, one and two peaks were observed for CO adsorption on the Rh-loaded and Rh single nanosized catalysts via in situ FT-IR measurements, respectively, while the vibrational frequency of NO remained almost the same. The gemi-dicarbonyl CO adsorption, which corresponded to the two CO adsorption peaks in the Rh single nanosized catalyst, was only stable for small Rh nanoparticles, such as Rh₄. This indicated that the Rh particle size varied markedly between the Rh single nanosized and Rh-loaded catalysts. The adsorption properties of CO were different because of the particle size difference. We clearly found that the high catalytic activity of the Rh single nanosized catalyst was due to the small particle size of the supported Rh.