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In order to reduce the NOx concentration in car exhausts usually the selective catalytic reduction with ammonia is used. However, to avoid the transport of ammonia in vehicles urea is applied as NH3 precursor. Controlled urea decomposition before the injection into the exhaust gas system itself may be accomplished by the use of a separate reactor. Urea decomposition to ammonia in the liquid phase under pressure in a heated reactor was compared to its decomposition in the gas phase. In the liquid phase, higher conversion rates relative to the reactor volume were realized than in the gas phase. Catalysts which showed high activity in the gas phase influenced the decomposition in the liquid phase only slightly. [ABSTRACT FROM AUTHOR]

Abstract: We report about a novel niobia-ceria based catalyst that may be applied for the selective catalytic reduction (SCR) of NO x as well as the catalytic regeneration of diesel particulate filters (DPF) in diesel engines. The material proved to be active in model gas experiments for a series of important reactions in these processes: (1) the SCR of NO with NH3, (2) the hydrolysis of urea to NH3 and (3) the oxidation of soot. The catalyst was able to convert 72% NO already at 250°C and showed almost full NO reduction between 300 and 450°C. The new niobia-ceria exhibited a similar urea hydrolysis activity as compared to a conventional TiO2 catalyst. A significant decrease of the soot oxidation temperature was also noticed with this catalyst. [Copyright &y& Elsevier]