Effect of Ageing Atmosphere on Three-way Catalytic Performance of Supported Rh Catalysts

Deactivation of a mixture of Rh/Al2O3 and CeO2-ZrO2 (CZ) by high-temperature ageing was clearly observed in three-way catalytic reactions under lean/rich perturbation conditions. The light-off temperature at which 50 % conversion was achieved was increased in the order of fresh < stoichi. approximate to rich < rich/lean < lean ageing conditions. Rh dispersion and presence of isolated Rh sites, revealed from in-situ FT-IR spectroscopy following CO adsorption, were responsible for the high light-off activity. NO conversion in higher temperature regions under lean/rich perturbation conditions was influenced by the ageing atmosphere. H-2-TPR measurements suggested the formation of Rh-CZ interactions with different strengths depending on the atmosphere during high-temperature ageing. The strength of the Rh-CZ interaction was suspected to be important to achieve high NO conversion in higher temperature regions.