Building Selectivity for NO Sensing in a NOx Mixture with Sonochemically Prepared CuO Structures

Max Mullen,Prabir Dutta

doi:10.3390/chemosensors4010001

Abstract

Several technologies are available for decreasing nitrogen oxide (NOx) emissions from combustion sources, including selective catalytic reduction methods. In this process, ammonia reacts with nitric oxide (NO) and nitrogen dioxide (NO2). As the stoichiometry of the two reactions is different, electrochemical sensor systems that can distinguish between NO and NO2 in a mixture of these two gases are of interest. Since NO and NO2 can be brought to equilibrium, depending on the temperature and the surfaces that they are in contact with, the detection of NO and NO2 independently is a difficult problem and has not been solved to date. In this study, we explore a high surface area sonochemically prepared CuO as the resistive sensing medium. CuO is a poor catalyst for NOx equilibration, and requires temperatures of 500 C to bring about equilibration. Thus, at 300 C, NO and NO2 retain their levels after interaction with CuO surface. In addition, NO adsorbs more strongly on the CuO over NO2. Using these two concepts, we can detect NO with minimal interference from NO2, if the latter gas concentration does not exceed 20% in a NOx mixture over a range of 100–800 ppm. Since this range constitutes most of the range of total NOx concentrations in diesel and other lean burn engines, this sensor should find application in selective detection of NO in this combustion application. A limitation of this sensor is the interference with CO, but with combustion in excess air, this problem should be alleviated.

Highlights

There are numerous studies of different electrochemical methods of sensing for nitric oxide (NO) and NO2 in the literature [1], but, interestingly, there are very few studies which focus on the detection of one of these gas species in a mixture of NO and NO2
NO is favored at high temperature, and NO2 is favored at low temperature
Advantage is taken of the fact that NO/NO2 equilibration is not significantly promoted over CuO at 300 ̋ C, each component, NO and NO2, maintain their identity

Summary

Introduction

There are numerous studies of different electrochemical methods of sensing for NO and NO2 in the literature [1], but, interestingly, there are very few studies which focus on the detection of one of these gas species in a mixture of NO and NO2. Most studies focus on detection of one of these gases and measure selectivity to one of these gases against the other with both in their pure form, in a balance of some mixture of N2 and O2. Measurement of NO and NO2 in a NOx mixture is made even more difficult since NO and NO2 can be in equilibrium. There are electrochemical sensors that can measure total NOx [2,3,4,5]. There can be a small amount of NO2 in these combustion

Objectives

Methods

Results

Discussion

Conclusion