Abstract
Thermal ageing has a significant detrimental effect on the behavior of bimetallic Pd–Rh natural gas fuelled vehicle (NGV) catalysts toward NO adsorption and its dissociation recognized as structure-sensitive. The ageing procedure at the lab-scale consisted of a thermal treatment under wet atmosphere (10vol.% H2O in air) at 980°C that would induce comparable surface reconstructions taking place under real exhaust conditions of Pd–Rh/Al2O3 catalysts. XPS and FTIR of CO adsorption highlight the occurrence of simultaneous particle sintering and preferential surface Rh enrichment. Temporal analysis of product (TAP) experiments have been implemented for in situ characterization that allows the elucidation of surface reactions and diffusion processes taking place at the surface of Pd–Rh/Al2O3 when single NO pulse is introduced. It was found that the relative rates of those processes are strongly affected by the dispersion and the Rh composition on freshly-prepared and aged catalysts. Interestingly, Rh recognized as the most suitable noble metal to convert NO to N2 would also slow down the agglomeration on Pd further protecting the metal/support interface.
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