The reactivity of Tan+ clusters with NO molecules: N-O bond dissociation and NOx conversion

Nitric oxides are primary contributors to air pollution. Examining their chemical transformations is crucial for developing effective clean air strategies. In this study, we studied the reactions between cationic tantalum clusters Tan+ (n = 1-16) and NO, utilizing our customized laminar flow tube reactor coupled with a tandem quadrupole mass spectrometer. The experimental results indicate that the reaction pathways of Tan+ clusters vary with cluster size: for smaller tantalum clusters Tan+ (n ≤ 5), the reaction products are mainly composed of TanN+ and TanO+, suggesting direct N-O dissociation or bimolecular reaction to release N2O or NO2 mediated by small metal clusters. In contrast, the larger clusters Tan≥6+ exhibit a range of reaction products, facilitated by the favorable adsorption of multiple molecules to generate the Tan(NO)m+ and TanO(NO)m+ series. Theoretical calculations reveal that the energetics and reaction dynamics differ among Tan+ clusters of varying sizes. This study clarifies the substantial size effect of the Tan+ clusters in reactions with nitric oxide and underscores the importance of small Ta clusters for NO elimination and NOx conversion.