Catalytic combustion reduces NOx formation. Since the concept benefits from combustion of the pre-mixed fuel/air over a honeycomb form of catalyst, the full-combustion occurs at relatively lower temperatures, and thus, leads to significantly lower NOx emission. The concept is successfully tested in stationary gas turbines where gas form fuel can easily be used. For airliners, however, the liquid fuel (e.g. kerosene) needs to be vaporized prior to mixing with air. Thus, the applicability of the concept is at present limited due to a lack of technological and constructive developments.
With the exhaust gas treatment technologies, the catalytic converter is placed at the post-combustion area. Currently, many materials and principles are suggested for effective NOx-reduction in exhaust gases. These function effectively under stochiometric A/F-ratios (λ > 1) as in Three-Way Catalysis (TWC) or under lean/rich-cyclic combustion conditions as in storage/reduction catalysis (SR-NOx). Selective catalytic NOx reduction by addition of NH3 as reductant is another concept which also works well, especially for stationary systems where the problems related to the presence of corrosive non-reacted ammonium are not regarded as important. As an alternative, hydrocarbons (HC) can be employed as reductant which is more suitable for mobile transport systems. However, in oxygen containing exhaust gases such as those in lean-burn diesel engines and turbines these concepts and materials display only a fraction of their performances which is detected under oxygen-free conditions. Therefore, there is a need for future applications to develop materials that are high-temperature stabile and catalytically active at temperatures above 600°C. These can be complex oxides from binary compounds with perovskite and spinel structures and/or ternary compounds of magnetoplumbite structure. These can accommodate many catalytic and sensing elements in their crystal structure and thus, are versatile and cheap to produce. Nano-sized noble metal clusters embedded in ceramic matrices are more complicated to manufacture and expensive, but are nevertheless promising alternatives.