Understanding Pt–Rh Synergy in a Three-Way Catalytic Converter

Abstract

Abstract NO reduction to N2 is the key reaction for efficient operation of a three-way catalytic converter (TWC). It is reported that metal catalysts Pt and Rh co-exist as individual metals in a TWC to give synergistic performance. In this article, we have studied the NO + CO reaction for a 1:1 physical mixture of silica supported Pt and Rh catalysts using fixed bed experiments and microkinetic modeling. The microkinetic model [14] for the reaction on single metals Pt and Rh is simulated for the mixture case in CHEMKIN PRO®. It is observed that the mixture maintains the activity while producing less N2O (by-product of NO + CO reaction) thus enhancing N2 selectivity inspite of having only half amount of Rh. Analysis of surface coverages on individual metals in mixture shows that in the presence of Pt, CO poisoning of Rh is reduced at lower temperature leading to better overall conversion and selectivity. This has potential benefit in automotive catalysis, as it results in the formation of significantly lower amounts of N2O, an undesirable side-product and greenhouse gas; at a lower cost than if pure Pt/Rh catalysts were used.