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

Artikel i vetenskaplig tidskrift, 2017

In the present study 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 using several high-resolution electron microscopy techniques like STEM, FIB/SEM slice & view, SEM and EDX. A combination of these analysis techniques and advanced TEM specimen preparation allowed for three-dimensional probing at different length scales avoiding the random character of conventionally crushed powder specimens due to site specificity. A core-shell distribution of Pt-Pd nanoparticles within the alumina support particles, with enlarged nanoparticles (≈ 1.5 to 40 nm) being 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.