This Small Business Innovation Research Phase I project will investigate the sensing mechanisms underlying a new nitrogen oxides (NOx) sensor technology that also has the potential for ammonia sensing. This project will optimize materials for dual NOx and NH3 sensing through experimentation and testing, establish mechanistic models for both NOx and NH3 sensing, and validate the mechanistic model. Currently commercially available NOx sensors fail to meet the accuracy, response time, and price requirements of these complex after-treatment systems. Ammonia or dual NOx /NH3 sensors are not available commercially. The small business has recently identified an electrocatalytic NOx sensor technology and has demonstrated the potential for significantly improved accuracy, sensitivity, and response time over the commercial technology. Through modification to the sensing electrode materials and sensor operating conditions, this sensor technology has also been demonstrated to be sensitive to ammonia. In this project, the NOx sensing mechanisms will be studied to develop this promising technology into an optimized, robust device. Additionally, the ammonia sensitivity will be investigated to establish a dual NOx /NH3 sensor for the diesel emissions after-treatment market.
The broader/commercial impact of this project will be the enhanced ability to monitor NOx, which is a major global pollutant and a precursor to acid rain, and ground-level ozone and smog formation. New environmental regulations are driving NOx emissions to increasingly lower levels, with the most challenging of these being the 2010 EPA Tier 2 diesel tailpipe standards. To meet these, engine manufacturers have been developing new diesel after-treatment technologies including selective catalyst reduction (SCR) systems and lean NOx traps and require both NOx and ammonia sensors for closed loop control and diagnostics of these systems. If successful, the new NOx sensor has the potential to significantly reduce emissions levels of these gases through more accurate and faster detection than the competition. Moreover, the additional NH3 sensitivity offers a solution for monitoring of ammonia slip, an issue for which no commercial sensor currently exists. With a >$1.2 billion market forecasted for 2012, the NOx /NH3 sensor has tremendous commercial potential. Additionally, the new sensor technology is expected to be a lower cost approach, enabling the diesel industry to have a sensor that meets both the technical and price requirements.
Nitrogen oxides (NOX) are a major global pollutant and a precursor to acid rain, ground-level ozone and smog formation. New environmental regulations are driving NOX emissions to increasingly lower levels, with the most challenging of these being the 2010 EPA Tier 2 diesel tailpipe standards. To meet these, engine manufacturers have been developing new diesel after-treatment technologies, the most prevalent being selective catalyst reduction (SCR) systems, in which ammonia is dispensed to reduce the NOX to N2 and H2O. While effective for meeting NOX regulations, excessive ammonia dosing is a common problem in SCR systems, and future regulatory control of ammonia emissions is anticipated. Sensors capable of accurate, real-time quantification of NOX and NH3 in the exhaust stream are needed for closed loop control of these systems, enabling diesel system manufacturers to meet these emissions regulations cost effectively. Currently, only one commercial NOX sensor exists, and it has insufficient response time and accuracy to meet the needs of these applications. Moreover, no commercial NH3 sensor exists today. A dual NOX /NH3 sensor, enabled by NexTech’s unique technology, therefore, offers a strong value proposition in diesel exhaust after-treatment systems and has tremendous potential market opportunity. NexTech offers a unique technology to address the need for diesel after-treatment systems, and because of the dual NOX and NH3 sensing capability, the technology presents a significant opportunity within the diesel industry. Development of a robust sensor product to meet the market’s future needs requires a fundamental understanding of the mechanisms of sensor response under anticipated operating conditions. In this Phase I SBIR project, NexTech investigated the fundamental responses of its sensor technology to NOX, ammonia, and background oxygen concentration under a range of sensor operating conditions, with focus on developing a mechanistic model for its NOX and NH3 sensing characteristics, as well as evaluating the sensor over a range of anticipated application conditions. Approaches employed in this project include current-voltage (I-V) testing, response cycle testing with systematic condition changes, and Diffuse Reflective Infrared Fourier Transform Spectroscopy (DRIFTS) analysis. During the Phase I project, NexTech has accomplished the technical goals set forth toward the enhancement of the dual NOX and NH3 sensor, summarized as follows: Fundamental response characterization tests yielded several important relationships between the operating conditions and performance of the sensor under NOX and NH3 additions into the test gas. These observations were leveraged into developing the model for the sensor mechanism. Conditions were identified at which the NOX and NH3 sensitivities could each be discretely optimized. The impact of background oxygen partial pressure was evaluated and observed to be minimal over a range of gas and temperature conditions, enabling accurate NOX and NH3 sensing even under varying application conditions. DRIFTS analysis has laid an excellent foundation for enhancing our understanding of the specific surface species formation or conversion under a variety of operating conditions. DRIFTS spectra were analyzed under conditions of varying NO, NO2, and NH3, as well as varying gas temperature and background gas conditions. Through these results, NexTech has developed a mechanistic understanding of the NOX and NH3 sensing properties of its dual NOX/NH3 sensor. Both gas bench characterization and DRIFTS analysis support the concept that the sensor exhibits different fundamental sensing mechanisms in the presence of these two gases. Through manipulation of operating parameters, dual sensitivity can be achieved in a single sensor.
