Cu model catalyst dynamics and CO oxidation kinetics studied by simultaneous in situ UV-Vis and mass spectroscopy

The oxidation state of Cu nanoparticles during CO oxidation in CO + O₂ gas mixtures was sensitively monitored via localized surface plasmon resonances. A microreactor, equipped with in situ UV-vis and mass spectrometry, was developed and used for the measurements. Cu nanoparticles of ∼30 nm average diameter were supported on optically transparent, planar quartz wafers. The aim of the study is 2-fold: (i) to demonstrate the performance and usefulness of the setup and (ii) to use the combined strength of model catalysts and in situ measurements to investigate the correlation between the catalyst oxidation state and its reactivity. Metallic Cu is significantly more active than both Cu(I) and Cu(II) oxides. The metallic Cu phase is only maintained under conditions where close to full oxygen conversion is achieved. This implies that kinetic measurements, aimed at determining the apparent activation energy for metallic Cu under realistic steady-state conditions, are difficult or impossible to perform.