J. Ceram. Sci. Tech., 08 [01] 19-24 (2017) DOI: 10.4416/JCST2016-00056 available online at: http://www.ceramic-science.com © 2017 Göller Verlag Optimisation of a Urea Selective Catalytic Reduction System with a Coated Ceramic Mixing Element M.A. Damm *1 , M. Sauerborn 1 , T. Fend 2 , U. Herrmann 1 1 Solar-Institut Jülich (SIJ), FH Aachen University of Applied Sciences 2 Institute for Solar Research, Facilities and Solar Materials received August 1, 2016; received in revised form October 3, 2016; accepted November 4, 2016 Abstract The selective catalytic reduction of NO x emissions to H 2 O and N 2 is a major technology in automotive applications for exhaust gas aftertreatment. In this process, the reactant ammonia (NH 3 ) is produced by injecting AdBlue®. With the help of an SCR catalyst, this NH 3 reduces emitted NOx to non-toxic nitrogen (N 2 ) and water (H 2 O). For the homogenization and evaporation of the urea solution, usually metallic mixing elements are used. The new approach uses a mixing element based on structured porous ceramic with an enlarged surface and a special catalytic coating. The Solar-Institut Jülich and the German Aerospace Centre have developed a manufacturing process to modify and optimise the structure of basic polyurethane foams to achieve a high NH 3 conversion rate in combination with adjustable backpressure. The optimised flow dynamics of the exhaust gas and the additional special catalytic coating lead to a high-performance mixing element. As a consequence, the size of the conventional SCR catalyst, which is located downstream of the mixer, can be reduced. This leads to cost-efficient and compact exhaust gas aftertreatment. In this paper the experimental results of the performance analysis of this newly designed porous-ceramic-coated mixing element will be presented. Keywords: Selective catalytic reduction system, selective catalytic reduction catalyst, mixing element, porous ceramic polyurethane foam I. Introduction The selective catalytic reduction (SCR) of NO x emis- sions to H 2 O and N 2 is a major technology in automotive applications for exhaust gas aftertreatment 1 . In this pro- cess, the reactant ammonia (NH 3 ) is produced by inject- ing a liquid water-urea solution (AdBlue ® ). In a thermal dissociation (Eq. 1.0) 2 and hydrolysis process (Eq. 1.1) 2 , the required NH 3 is formed. (NH 2 ) 2 CO → NH 3 + HNCO (thermal dissociation) (1.0) HNCO + (H 2 O) * → NH 3 + CO 2 (hydrolysis) (1.1) With the help of an SCR catalyst, this NH 3 reduces emit- ted NOx to non-toxic nitrogen (N 2 ) and water (H 2 O) e.g. according to Eq. 1.2 2 : 4 NO + O 2 + 4 NH 3 → 4N 2 +6H 2 O (SCR) (1.2) The chemical reaction has to be supported by a catalyst in order to accelerate the hydrolysis reaction and to avoid the production of solid polymerization products with high thermal stability from the acid component HNCO 3, 4 . The catalyst for the hydrolysis reaction can be integrated in the SCR catalyst or synthesized as a single component with an additional SCR catalyst. According to the state of the art, the atomization of the injected urea solution is improved by increasing the pres- sure of the AdBlue® injection to achieve adequate distri- * Corresponding author: damm@sij.fh-aachen.de bution and rapid formation of NH 3 . Such low-cost pulsed pressurised atomizer systems need a static mixing element in front of the SCR catalyst for effective distribution of the reactant concentration in the inflow of the SCR cat- alyst 5 . For the homogeneous nebulization and complete evaporation of the urea solution, usually metallic mixing elements are used 6 . These systems need a large volume for all their required components, especially the SCR catalyst, and are very expensive. In these applications, the mixing elements act only as a mixer. An overview of the classic SCR system can be seen in Fig. 1 7 . The new approach presented in this paper uses a mixing element based on structured porous ceramic with an enlarged surface and a special catalytic coating. A struc- tured porous ceramic offers in this way a high specific sur- face which is needed for the functionality as a catalyst. The catalytic coating is applied to accelerate the hydrol- ysis reaction (Eq. 1.1) and to achieve a high NH 3 conver- sion rate. The body material of the mixing element is made of clay-based porous ceramic which is manufactured from blanked polyurethane foam in the Schwartzwalder pro- cess. The Solar-Institut Jülich and the German Aerospace Center have developed a manufacturing process to mod- ify and optimise the structure of the basic polyurethane foam to achieve the high NH 3 conversion rate in combi- nation with adjustable backpressure. The optimised flow