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In this project funded by the Bayerische Forschungsstiftung two fundamental investigations had been carried out: first a new N-rich liquid ammonia precursor solution based on guanidine salts had been completely characterized and secondly a new type of side-flow reactor for the controlled catalytic decomposition of aqueous NH₃ precursor to ammonia gas has been designed, applied and tested in a 3-liter passenger car diesel engine. Guanidine salts came into the focus due to the fact of a high nitrogen-content derivate of urea. Specially guanidinium formate has shown extraordinary solubility in water (more than 6 kg per 1 liter water at room temperature) and therefore a possible high ammonia potential per liter solution compared to the classical 32.5% aqueous urea solution (AUS32) standardized in ISO 22241 and known as DEF (diesel emission fluid), ARLA32 or AdBlue® .

The NO reduction in an ammonia SCR converter has been simulated by a 1D+1D model for a single representative channel to parametrically study the characteristics of the system under typical operating conditions. An appropriate model has been selected interpreting the chemical behavior of the system and the parameters are calibrated based on a comprehensive set of experiments with an Fe-Zeolite washcoated monolith for different feed concentrations, temperatures and flow rates. Physical and chemical properties are determined as well as kinetics and rate parameters and the model has been verified by experimental data at different operating conditions. Three different mechanisms for the surface kinetics to model NO reduction have been assessed and the results have been compared in the cases of steady DeNO performance and transient response of the system. Ammonia inhibition is considered in the model since it has a major effect specifically under transient operating conditions.

The reduction of NOx using NH₃ has been successfully practiced for stationary sources and more recently, for passenger cars and heavy-duty applications in the US and Europe. Due to the up-coming Euro 6 regulations (2014) for passenger cars and light-duty trucks, NH₃-SCR catalyst technologies are extensively studied by OEMs, catalysts manufacturers and raw materials suppliers, all looking for technologies very efficient at low temperatures, thermally stable up to 800°C and with a limited impact of the NO₂/NOx ratio on activity. Among the new emerging SCR catalytic systems, non-zeolitic zirconia-based mixed oxides were introduced recently in SAE 2008 as promising new SCR catalysts. This paper reports the progress made on these materials. "Synthetic Gas Bench Tests" performed on powder catalysts show a significant increase of the NOx conversion, in comparison with that previously reported.