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.
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