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

Abstract

In this study, adsorption energies and reaction energetics on (111) 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 H2 in assisting NO dissociation and removing surface O* under stoichiometric and fuel-lean conditions. However, it presents high NH3 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 O2. 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 H2 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.