Catalytic Oxidation of NO on [Au M]- (M = Pd and Pt) Bimetallic Dimers: An Insight from Density Functional Theory Approach

Escalation of nitrogen monoxide (NO) concentration into the atmosphere has caused severe environmental problems. So, it is important to prepare or design a suitable catalytic system to understand the oxidation of NO into NO2 at the molecular level. In this regard, a comprehensive theoretical investigation of the catalytic oxidation of NO on anionic bimetallic dimers [Au-M](-) (M = Pd, Pt) has been considered here using the density functional theory method at the M06L functional along with def2TZVP basis set. To refine the energies and electronic properties of all species, single-point energy calculations are further performed with the CCSD(T) method using the same basis set. The adsorption of NO and O-2 on bimetallic dimers is studied, and binding energy has been calculated to understand the stability of the adsorbed species. Our calculations show that M sites are found to be the preferred site for adsorption rather than Au site. Further, full catalytic reaction pathways using the Langmuir-Hinshelwood mechanism are investigated in which two NO molecules are converted into two NO2 molecules in the presence of an activated O-2 molecule. Moreover, an energetic span model has justified that conversion on [Au-Pd](-) catalyst possesses a lower apparent activation energy than that on [Au-Pt](-) which makes [Au Pd](-) a more efficient catalyst toward the catalytic conversion of NO into NO2. Thus, the present study will convey an understanding of the mechanism of NO oxidation at the molecular level as well as designing better catalysts for future prospects.