Comparative analysis of NOx reduction on Pt, Pd, and Rh catalysts by DFT calculation and microkinetic modeling

• DFT calculation was performed to identify the reaction mechanism of NO reduction on Pt, Pd and Rh catalysts under TWC conditions. • On the Pt catalyst, H 2 plays important roles to assist NO dissociation and to remove surface O*. • On the other hand, Rh showed strong NOx, N 2 and O 2 adsorption and NO was easily dissociated on the surface regardless of reducing agent. • Rh + Pt catalyst exhibits the excellent NO reduction activity under overall TWC condition. In this study, adsorption energies and reaction energetics on (1 1 1) surfaces of Pt, Pd and Rh were established using DFT calculation. Based on these thermodynamic results, reactant conversions and product yields of Pt, Pd and Rh catalysts under various air-fuel ratio (λ) were predicted by microkinetic modeling combined with simulated packed bed reactor. As a result, Pt catalyst efficiently utilizes H 2 in assisting NO dissociation and removing surface O * under stoichiometric and fuel-lean conditions. However, it presents high NH 3 yield under stoichiometric and fuel-lean conditions. Conversely, Rh catalyst show high NO reduction activity under fuel-rich condition while it hardly reduce NO in presence of O 2 . In order to take the advantages of both catalysts, we suggest physically-mixed Rh + Pt catalyst is excellent catalyst using the advantages of each catalyst for TWC. Consequently, it is confirmed that Pt sufficiently reduces NO using H 2 under stoichiometric and fuel-lean conditions, and Rh easily dissociates NO at low temperature under fuel-rich condition when using the Rh + Pt catalyst. We expect that identifying the reaction characteristics of TWC components under different λ conditions will help to propose future TWC design.