Three‐Dimensional Probing of Catalyst Ageing on Different Length Scales: A Case Study of Changes in Microstructure and Activity for CO Oxidation of a Pt–Pd/Al₂O₃ Catalyst

Abstract

The effects of thermal treatment on the microstructure of a Pt–Pd/Al2O3 oxidation catalyst and its activity for CO oxidation have been studied. The microstructural analysis was performed by using several high‐resolution electron microscopy techniques such as STEM, FIB/SEM slice & view, SEM and EDX. A combination of these analytic techniques and advanced TEM specimen preparation allowed for three‐dimensional probing at different length scales, avoiding the random character of conventionally crushed powder specimens owing to site specificity. A core–shell distribution of Pt–Pd nanoparticles within the alumina support particles, with enlarged nanoparticles (≈1.5 to 40 nm) present in the shell and small nanoparticles (<1.5 nm) in the core, was revealed in the untreated catalyst. A more uniform spatial distribution developed during thermal treatment at 700 °C or higher with larger nanoparticles forming in the core. Accompanying measurements of the catalytic activity for CO oxidation showed the detrimental effect of sintering of the small nanoparticles on the reaction rate and apparent activation energy of the reaction.