Solid state electrochemical DeNOx—An overview

doi:10.1016/j.apcatb.2010.09.002

Applied Catalysis B: Environmental

Volume 100, Issues 3–4, 20 October 2010, Pages 427-432

https://doi.org/10.1016/j.apcatb.2010.09.002 Get rights and content

Abstract

The literature on direct electrochemical reduction of NO_x in a solid state cell has been reviewed. It is shown that the reduction of nitric oxide either occurs on the electrode or on the electrolyte if F-centers are formed. It is also shown that some oxide based electrodes has a high apparent selectivity towards the reduction of nitric oxide in a net oxidizing atmosphere. The activity and apparent selectivity of oxide based electrodes is strongly dependent on the composition of the oxide. The selectivity of noble metal based electrodes is generally very low. However, coating of noble metal based electrodes can give current efficiencies of up to 20% even in the presence of large amounts of oxygen.

Graphical abstract

Research highlights

▶ Solid state electrochemical DeNO_x is reviewed. ▶ Noble metals show only little use as cathodes for electrochemical DeNO_x. ▶ Noble metals with coatings show promising use as cathodes for electrochemical DeNO_x. ▶ Some oxides also show promising use as cathodes for electrochemical DeNO_x.

Introduction

The exhaust gas emitted from the combustion process of fossil fuels contains significant amounts of NO_x [1]. The emission of NO_x is highly unwanted, as NO_x lead to the formation of smog and acid rain [2], [3]. Several processes are known that can reduce the NO_x from diesel exhausts. The best known commercial solution is the selective catalytic reduction (SCR) of NO_x using urea as a reducing agent [4]. The main problems with this method is that the reducing agent has to be stored on-board the vehicle, and that possible slip of the reducing agent is a serious threat. The formation of nitrous oxide (a powerful greenhouse gas) is another problem, that hasn’t been solved [5]. Electrochemical reduction of NO_x in an all solid state electrochemical reactor is a potential attractive technique [6]. In electrochemical reduction of NO_x current is used instead of a reducing agent. The concept is shown in Fig. 1. In the figure it is seen that nitric oxide is reduced at the cathode to nitrogen and oxide anions. The oxide anions are transported through the electrolyte to the anode where oxygen is formed. Some reviews on solid state electrochemical DeNO_x have already been published most of them several years ago [6], [7], [8], [9], [10]. This is an up to date and more in depth review.

Section snippets

General considerations

The constituents and the temperature of the exhaust of different types of engines are shown in Table 1. It is seen that the exhaust of a typical diesel engine contains 200–1000 ppm of NO_x, besides other pollutants. In this context the high amount of oxygen present in the exhaust gas should be noted.

Solid state electrochemical DeNO_x is build on the SOFC technology. The operation temperature of the SOFC is typically around 750 °C. The temperature of the exhaust gas of a diesel engine is much lower,

Literature survey

Early work. The idea of reducing NO_x electrochemical in an all solid state cell was first suggested by Pancharatnam et al. [11] in 1975. Using a Scandia Stabilized Zirconia (SSZ) electrolyte and either porous platinum or porous gold electrodes they showed that nitric oxide could be reduced at the cathode to N₂ and oxide anions in the temperature range of 600–800 °C. By applying very high over-potentials (−2.2. V vs. air) it was furthermore shown that the rate of the reduction of nitric oxide

Conclusion

Good progress has been made in identifying electrodes for direct electrochemical reduction of nitric oxide under net oxidising conditions. It has been shown that several oxide based electrodes has a high apparent selectivity towards the reduction of nitric oxide. It has likewise been shown that coating of metal based electrodes can lead to current efficiencies of up to 20% even in the presence of high amounts of oxygen. Removal of nitric oxide using a full ceramic cell has been proved possible.

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ReviewSolid state electrochemical DeNOx—An overview

Abstract

Graphical abstract

Research highlights

Introduction

Section snippets

General considerations

Literature survey

Conclusion

Prog. Energy Combust. Sci.

Appl. Catal. B: Environ.

Appl. Catal. B: Environ.

Solid State Ionics

Solid State Ionics

Solid State Ionics

Solid State Ionics

Solid State Ionics

Solid State Ionics

Solid State Ionics

Solid State Ionics

Mater. Res. Bull.

J. Eur. Ceram. Soc.

Appl. Catal. B: Environ.

Solid State Ionics

Solid State Ionics

Chem. Eng. Sci.

Surf. Sci.

Surf. Sci.

Science

Science

Catal. Today

Catal. Rev. Sci. Eng.

Electrochemical Activation of Catalysis

Chinese J. Catal.

Ionics

J. Electrochem. Soc.

J. Electrochem. Soc.

J. Electrochem. Soc.

Review
Solid state electrochemical DeNO_x—An overview