A new research project for the knowledge-based development of precious metal catalysts for the reduction of nitrogen oxides using hydrogen (H₂-DeNO_x) was launched in November 2019. The research project is funded by the Sächsische Aufbaubank (SAB) and the European Regional Development Fund (ERDF).

Combustion engines based on liquid and gaseous fuels make an important contribution to securing mobility and generating heat and electricity, e.g. in decentralized combined heat and power (CHP) plants. In particular, motorized combined heat and power plants with cogeneration play a key role against the backdrop of the German government's climate plan ("energy transition"), as they are able to provide energy flexibly when the fluctuating "renewable" energy sources of wind and sun are not available in sufficient quantities.

However, combustion engines achieve high levels of efficiency and therefore lower CO₂ emissions, particularly under lean, i.e. oxygen-rich, combustion conditions. The high efficiency levels are offset by the emission of pollutants, in particular nitrogen oxides (NO_x).  However, with the established processes for nitrogen oxide reduction, selective catalytic reduction using ammonia (SCR) and NO_x storage catalysts (NSC), a significant reduction in NO_x emissions can only be achieved from around 200°C upwards. In real operation, however, the exhaust gas temperatures of diesel engines are often below 200°C, and in CHP applications, temperatures after the heat exchanger are only 120°C. The only method for NO_x reduction at low exhaust gas temperatures in oxygen-rich exhaust gases is the use of hydrogen as a reducing agent (H₂-DeNO_x). However, the platinum and palladium catalysts that are effective for this reaction have the disadvantage that the nitrogen oxides are not completely converted to N₂ at the catalysts, but also partially to N₂O. However, N₂O has a 310 times greater greenhouse effect than CO₂, so its emission must be avoided at all costs.

The scientific and technical objective of the RedNOx project is therefore the knowledge-based development of a new type of catalyst for efficient NO_x reduction using H₂ in lean exhaust gases. The catalyst developed should have the following properties:

• High H₂-DeNO_x activity between approx. 120 and 250°C
• Selective NO_x reduction to N₂ (no N₂O formation)
• High selectivity of H₂ for NO_x reduction compared to the reaction with O₂

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