Electrochemical reduction of NOx - DTU Orbit

4 DRIFT study of NOx adsorption on CGO10 impregnated with K2O or BaO
1520-1580 cm -1 and 1200-1250 cm -1 can be ascribed to NO3 - . However, it should be mentioned,
Cerrutti et al. ascribed peaks at 1208-1222 cm -1 to chelating NO2 - instead of NO3 - 128 , but the broad
shape of the peak around 1200 cm -1 observed in this work also indicates the peak may be due to
several adsorbed species, for instance due to both NO3 - and chelating NO2 - adsorbed on the CGO
surface.
With respect to the region around 1600 cm -1 only one, clearly distinctive peak is observed at 500
°C at 1573 cm -1 , ascribed to NO3 - (see above). The peak at 1573 cm -1 has two low asymmetric
shoulders on the left/high wavenumber side. When the temperature is decreased to 300 °C, these
two shoulders increase in size, and in addition two peaks appear at 1603 and 1610 cm -1 ,
respectively. By comparison to literature these two peaks are suggested to be due to adsorbed
NO - and adsorbed NO2, as these two species were ascribed by Busca et al. to 1595 cm -1 and 1605
cm -1 126 , respectively. It also seems reasonable that more weakly adsorbed species like NO - and
NO2 only adsorbs at lower temperatures as observed in this work, while at 500 °C only strongly
adsorbed species like NO3 - can stay adsorbed on the CGO surface.
Finally minor peaks are observed at 1673-1680 cm -1 , 1720 cm -1 and 2207-2212 cm -1 , and suggested
to be due to N2O4 126 , cis-N2O2 2- 129 and N2O 114, 126, 130 respectively.
4.4.2 Influence of gas phase conditions on the formation of surface species
The adsorption peaks described in the previous section were observed on DRIFT spectra recorded
on a non-impregnated CGO10 sample subjected to 1000 ppm NO + 10% O2. Spectra were also
recorded on non-impregnated CGO10 while subjected to three other atmospheres: 1000 ppm NO,
1000 ppm NO2 and 1000 ppm NO2 + 10% O2. In general the spectra recorded in 1000 ppm NO +
10% O2, 1000 ppm NO2 and 1000 ppm NO2 + 10% O2 look very much alike (se Figure 11 and Figure
12), with dominating peak groups located at ≈1600 cm -1 and ≈1200 cm -1 , ascribed as previously
mentioned to adsorbed NO2 (≈1610 cm -1 ), NO3 - (≈1580 cm -1 ), and at 1197-1245 cm -1 overlapping
NO3 - and NO2 - peaks. In addition to these peaks smaller peaks ascribed to N2O (2207 cm -1 ) 130 , cis-
N2O2 2- (≈1720 cm -1 ) 129 , N2O4 (1671-1680 cm -1 ) 126 and NO2 (1610-1614 cm -1 ) 126 are also observed.
On the spectra recorded in 1000 ppm NO + 10% O2 an extra peak is visible at 1603 cm -1 in between
the 1610 cm -1 and 1580 cm -1 peak (see Figure 10), which likely can be ascribed to NO - 126 . From the
results it is not possible to conclude, whether this peak is not present in the NO2 containing
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