SCR-Urea Reactions

Concentrated aqueous solutions of Urea (32.5% urea) which is known as diesel exhaust fluid (DBF) (with the trade name AdBlue) are used for this deNOx reaction with dosing levels related to the engine operating temperatures (which are a proxy for engine out NOx emissions) [48]. 

In terms of additional catalytic requirements a catalyst might be required to promote the controlled hydrolysis of urea to generate NH. Lewis acids such as TiO are effective catalysts for this reaction [49]. The use of other materials (e.g. Bronsted acids) can result in unselec-tive hydrolyses with side products such as melamine being formed [50]. In more cases, however, the urea solution is injected into a heated zone where thermal hydrolysis generates 2 equivalents of NH and 1 CO for each urea molecule [51]. 

The material nanocomposite material described later (Section 1.3) uses solutions of urea as a source of NH for use in the SCR deNOx reaction. 

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Sullivan, J.A. and Keane, O. (2005). The role of Bronsted acidity in poisoning the SCR-urea reaction over FeZSM-5 catalysts. Appl Catal B Environ., 61, 244-252. 

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