Electrochemical reduction of NOx - DTU Orbit

4 DRIFT study of NOx adsorption on CGO10 impregnated with K2O or BaO
When the spectra recorded in 1000 ppm NO are compared to the spectra recorded in the three
other atmospheres significant differences are observed, mainly as much fewer peaks are present
in the IR spectra when the sample is supplied with only 1000 ppm NO in Ar. At 300 °C three
adsorption peaks are clearly visible, at 1560 cm -1 , 1269 cm -1 and 1211 cm -1 , as in the previous
section these peaks are ascribed to NO3 - (1560 cm -1 , 1269 cm -1 , 1211 cm -1 ) and/or NO2 - (1269 cm -1 ,
1211 cm -1 ). At first hand it is surprising to find dominating peaks due to a NO3 - , i.e. a highly
oxidized NO specie, when there is no oxygen in the atmosphere and also since the IR spectra
recorded by Philip et al. under similar conditions mainly seemed to be dominated by NO2 -
species 116 . Still the results in this work indicate, when CGO10 is supplied with 1000 ppm NO at 300
°C, NO is adsorbed and NO3 - are formed by reaction of the NO with adsorbed oxygen or lattice
oxygen at the CGO10 surface. It should be kept in mind; the CGO surface due to the pre-treatment
in 10% O2 likely is fairly rich in O2 from the beginning of the experiment.
At 500 °C it is not possible to observe adsorption peaks at all, but curiously enough two clear
desorption peaks are observed at 1552 cm -1 and 1255 cm -1 , i.e. almost exactly at the wavenumbers
where the NO3 - /NO2 - adsorption peaks were observed at lower temperatures, see Figure 12. This
could indicate that when the background spectrum was recorded, i.e. prior to the treatment in
NO-containing atmosphere, a small amount of NO was already adsorbed on the CGO and this NO
then subsequently is removed at 500 °C when the sample is treated in 1000 ppm NO without O2. It
is unknown where this small amount of pre-adsorbed NO should have come from, as the sample
prior to experiment had not been near any NO source, and the experimental set-up was flushed in
10% O2 between all the experiments to avoid any residual NO in the gas supply system during the
start-up of a new experiment.
A summary of the NO-related peaks observed in the four different atmospheres is given in Table 3
together with the assignment of the peaks to different NOx-species. The wavenumbers are stated
for peaks observed at 300 °C, and if the wavenumber is written in bold the peak was also observed
at 500 °C.
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