Electrochemical reduction of NOx - DTU Orbit

4 DRIFT study of NOx adsorption on CGO10 impregnated with K2O or BaO
4.4.3 Influence of catalyst composition on the formation of surface species
Already on the background spectra recorded in 10% O2 a clear difference is seen between the non-
impregnated and the K2O impregnated sample, see Figure 13. On the K2O impregnated sample
four negative peaks are observed a 2757, 2400, 2069 and 1767 cm -1 . Negative peaks observed on
background spectra are caused by IR-absorbing species and the 4 aforementioned peaks
correspond exactly to the 4 peaks measured for KNO3 by Bates et al. 136 . The presence of KNO3 is
somewhat surprising, since the sample during the preparation was heated to 700 °C, and the KNO3
by this was expected to decompose to K2O. However, from the background spectra it must be
concluded that either was all the KNO3 not completely thermally decomposed, or the K2O has after
the heat-treatment at 700 °C taken up some NOx and formed KNO3 again.
Signal [Volts]
3.0
2.5
2.0
1.5
1.0
0.5
0.0
4000
non-impregnated
K 2 O impregnated
3500
3000
2500
Wavenumber [cm-1]
Figure 13. Comparison between background spectra recorded at 500 °C in 10% O2 on non-
impregnated and K2O impregnated sample.
The absorbance spectra recorded on the K2O impregnated sample looks much different compared
36
2000
1500
1000
to the spectra recorded on the non-impregnated sample, see Figure 14 for comparison of the
spectra recorded at 300 °C and 500 °C in 1000 ppm NO +10% O2 and Table 4 for an overview of the
peaks observed at 300 °C and 500 °C . For the K2O impregnated sample the IR spectra show four
significant adsorption peaks at 2757, 2400, 2069 and 1767 cm -1 , which as just described are due to
KNO3 136 . A few other adsorption peaks are also observed at 300 °C at the following wavenumbers:
1883 cm -1 (NO on potassium) 137 , 1514 cm -1 (NO3 - ) 126 and 1343 cm -1 (NO3 - in KNO3) 136 . As for the