Size-dependent reactivity of Rh cationic clusters to reduce NO by CO in the gas phase at high temperatures.

The reactivity of the reduction of NO pre-adsorbed on Rh 2-9 + clusters by CO was investigated using a combination of an alternate on-off gas injection method and thermal desorption spectrometry. The reduction of Rh n N x O y + clusters by CO was evaluated by varying the CO concentration at T = 903 K. Among the Rh n N x O x + clusters, the Rh 3 N 2 O 2 + cluster exhibited the highest reduction activity, whereas the other clusters, Rh 2,4-9 N x O x + , showed lower reactivity. Density functional theory (DFT) calculations for Rh 3 + and Rh 6 + revealed that the rate-determining step for NO reduction in the presence of CO was NO bond dissociation through the kinetics analysis using the RRKM theory. The reduction of Rh 3 N 2 O 2 + is kinetically preferable to that of Rh 6 N 2 O 2 + . The DFT results were in qualitative agreement with the experimental results.