Liquid-Phase Catalytic Decomposition of Novel Ammonia Precursor Solutions for the Selective Catalytic Reduction of NO_x

Aqueous solutions of NH₃-precursor compounds (i.e. urea and methanamide) were catalytically hydrolyzed in the liquid phase by applying a pressure of 50 bar during contact with the catalyst in a heated tube. Methanamide could be hydrolyzed on an Au/TiO₂ catalyst to yield not only NH₃, but also H₂. Decomposition of urea under high pressure in the liquid phase could even be achieved without the addition of a catalyst. Due to the large excess of water present during decomposition, side products could be avoided. As the reactor tube is electrically heated, the presented method provides a possibility to reliably transform NH₃-precursor compounds into gaseous NH₃ independent of the engine exhaust gas temperature. The NH₃-flow can be added to the main exhaust duct to enable the selective catalytic reduction of NO_x at the light-off of the SCR catalyst.