Deactivation of commercial three-way catalysts: effect of the thermal ageing

Licentiate thesis, 2010

This licentiate thesis is a summary of my study on thermal deactivated commercial three way catalysts (TWCs). The experiments were performed using gasoline and a E85 fuel mixture of 85 vol.% ethanol and 15 vol.% gasoline. Gas composition, temperature, space velocity and stoichiometry were kept to levels similar to automotive conditions. The effect of hydrothermal ageing on mono- and bimetallic commercial TWCs was investigated. The analysis showed clear deactivation of the aged samples and the influence on TWC’s properties, such as: light-off temperature, specific surface area (BET), noble metal dispersion, oxygen storage capacity (OSC), oxygen storage capacity complete (OSCC) and labile oxygen storage capacity (LOSC). Water inhibition has been investigated and confirmed for the performance of NOx reduction of the fresh catalyst. Xray photoelectron spectroscopy (XPS) was used to measure changes in the oxidation state of the Pd and Rh present in the washcoat of the catalyst before and after hydrothermal ageing. An element map SEM-EDX analysis was performed in order to characterize the design and morphology of the catalysts, as well as their surface’s composition and distribution. In this work, theoretical and methodological contributions to deactivation of the catalysts are presented.