US EPA

1693896 

Journal Article 

Development of multifunctional NOx-catalysts and -sensors 

Saruhan, B; Stranzenbach, M 

2005 

1 

Materials Science Forum
ISSN: 0255-5476
EISSN: 1662-9752 

MATERIALS SCIENCE FORUM 

492-493 

249-254 

WOS:000230986100041 

High temperature lean burners in combustion system are one of the most effective approaches for the improvement of the energy efficiency in gas turbine engines. However, such systems are prone to produce toxic gases causing acid rain and greenhouse effect leading to air pollution. It is the future policy of European Union to achieve efficient and environment-friendly energy generation by targeting low to zero emission in power plant technology and aircraft traffic. Stringent legislation concerning such emissions for vehicles are already underway and is expected to be released for turbine engines, especially for those located in or near urban areas.



Catalytically stabilized combustion is an attractive technique because it offers the potential of ultra-low NOx emissions (< 3 ppm), improved flame stability and fewer pulsations. Possible positions to situate the catalytic converters in air-craft engines are hot areas such as within combustion chamber and at hot-gas outlets behind the chamber, requiring high-temperature stability of materials.



The catalytic system consists of ceramic layers with unique microstructures fulfilling the needs of being smart but low cost. For removal of CO, NOx, and HCs, complex oxides are used such as nano-composites of CexZr1-xO2-y with a higher effective surface which yield much better catalytic activity. Another group of materials which delivers preliminary promising results in terms of NO reduction is the Hexaluminates. Mn-substituted La-Hexaluminates with their magnetoplumbite crystal structure having large amount of interstitial oxidation sites and oxygen vacancies provide catalytic combustion by reducing NOx effectively during propulsion. In another approach, nano-sized noble metal particles embedded in ceramic matrices allow an effective fuel-rich catalytic combustion. This paper evaluates the catalytic materials and defines their use and advantages.



Lean premixed combustion is considered for both stationary and mobile gas turbines and engines. It is very attractive in terms of increased engine efficiency but poses higher NOx-emission and some practical problems. Since such engines operate near the lean stability limit, under these conditions, incidents such as flame out, flame instability or pressure waves induced flashback may occur. Thus, it is crucial that combustion is controlled by sensors to monitor the process, operate the flame in a safe range and detect rapidly the occurrence of combustion instabilities. The sensor shall take a two-fold task and control the combustion and regenerate the catalyst. The principles for sensing techniques and requirements for sensor materials for each application area are specified. 

gas-sensors; catalytic conversion and activity; magnetoplumbite; NOx-reduction; coatings