Selective Catalytic Reduction of NOx with H₂ for Cleaning Exhausts of Hydrogen Engines: Impact of H₂O, O₂, and NO/H₂ Ratio

A key concept for hydrogen-fueled internal combustion engines is reducing NOx emissions with direct H2-SCR. Besides platinum as an active noble metal component, palladium-based catalysts are attractive for NO reduction with high selectivity. However, reliability of the catalytic activity in the presence of water with persistently low side product formation remains challenging. Therefore, a monolithic 1%Pd/5%V2O5/20%TiO2-Al2O3 model catalyst is studied extensively under different conditions, showing that NOx conversion remains high even in the presence of 5% water, maintaining over 65% selectivity toward N2. Additionally, the catalyst remained active in a long-term experiment over 12 h in the absence and presence of water with an NO conversion over 45%. Finally, steady-state measurements and a kinetic analysis reveal overall concentration dependencies alongside trends of the reduction reaction competing with the hydrogen combustion reaction.