Hydrogen-fueled internal combustion engines are a promising CO₂-free and zero-impact emission alternative to battery or fuel cell electric powertrains. Advantages include long service life, robustness against fuel impurities and a strong infrastructural base with existing production lines and workshop stations. In order to make hydrogen engines harmless in terms of pollutant emissions as well, NO_X emissions at the tailpipe must be reduced as low as the zero-impact emission level. Here, the application of selective catalytic reduction (SCR) catalysts is a promising solution that can be rapidly adopted from conventional diesel engines.

This paper therefore investigates the influences of the hydrogen concentration in the raw exhaust gas, of the NO₂/NO_X ratio and of the space velocity on the performance of two different SCR technologies. The results show that both types of SCR, copper-zeolite and vanadium-based, have their advantages and drawbacks. Copper-based SCR catalysts have an early light-off temperature and reach maximum efficiencies of up to >99%. On the other hand, vanadium systems promise almost no secondary N₂O emissions. As a result, we combined both approaches to create a superior solution with high efficiency and lowest secondary emissions.