NO Adsorption and Reaction on Aged Pd–Rh Natural Gas Vehicle Catalysts: A Combined TAP and Steady-State Kinetic Approach

SSCI-VIDE+ING+YSC:CMIInternational audienceA combined temporal analysis of products (TAP) and steady-state kinetic study was achieved to characterize the surface reactivity of fresh and aged bimetallic Pd-Rh/Al2O3 Natural-Gas Vehicle catalysts. Single NO pulse TAP experiments were performed on a stabilized surface after exposure to successive NO pulses until to get a steady-state NO conversion. Outlet flow curves recorded during such experiments show fast reaction steps taking place on noble metal particles and a slow process during NO desorption ascribed to the involvement of spill-over effect of chemisorbed NO molecules from the metal to the support. This slow process attenuates on the aged sample likely due to an alteration of the metal/support interface induced by particle sintering at high temperature. Thermal aging also alters the surface composition of bimetallic Pd-Rh particles which leads to changes in the products distribution from NO dissociation. A similar selectivity behavior is observed from steady-state kinetic measurements during the NO/H-2 reaction. Interestingly, a weak partial pressure dependency of the selectivity reflects a surface Rh enrichment of Pd-Rh particles during aging