Electrochemical reduction of NOx - DTU Orbit

1 Introduction
when a square-wave voltage was applied rather than DC voltage 44 . In a series of papers Lucas-
Consuegra et al. reported on an electrochemically assisted NSR catalyst consisting of a Pt/K-βAl2O3
cell 46-48 . The Pt/K-βAl2O3 cell investigated by Lucas-Consuegra et al. showed the best performance
at 300 °C, and two different forms of nitrate were identified to be formed during the storage
process: a weakly bonded surface nitrate and a bulk nitrate 46 . Furthermore the influence of water
in the gas was investigated, and even though the performance of the catalyst decreased during
wet conditions, the decrease was not detrimental 46, 47 . Yoshinobu et al. reported recently studies
on electrochemical deNOx in combination with electrochemical oxidation of particulate matter
(PM); the studies were made both in a disk-electrode set-up and in a honeycomb module tested in
real diesel engine exhaust 49 . The electrodes investigated were composite electrodes of Pt or Ag in
combination with YSZ or CGO 49 . The addition of BaO to the electrodes was proven to be crucial for
the NOx conversion, however in the presence of CO2 a performance decrease was observed due to
the formation of BaCO3 49 . During the tests in real engine exhaust 97 wt% of the PM was removed
and 74% of the NOx was reduced at a fuel penalty of 9%, which are promising results, however a
higher NOx conversion and lower fuel penalty must be achieved for the technology to become
commercially attractive 49 .
1.3 Objective and lay-out of the thesis
This projects deals with electrochemical deNOx, a method under development for NOx removal
from automotive diesel engines. The objective of the PhD project is to investigate how the NOx
conversion during electrochemical deNOx is affected, when NOx-storage compounds are added to
noble metal-free ceramic electrodes. The investigation is centered around three main questions:
1) How much is the activity and selectivity of the ceramic electrodes towards NOx conversion
affected by the addition of a NOx storage compound?
2) What are the optimal conditions for NOx conversion on ceramic electrodes combined with
NOx storage compounds?
3) Which mechanisms/reaction steps are included in the oxidation/storage of NOx on the
electrodes and the subsequent reduction?
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