NDLI: Decomposition of Urea in the SCR Process: Combination of DFT Calculations and Experimental Results on the Catalytic Hydrolysis of Isocyanic Acid on TiO$_{2}$ and Al$_{2}$O$

Content Provider	Springer Nature Link
Author	Czekaj, Izabela Kröcher, Oliver
Copyright Year	2009
Abstract	In selective catalytic reduction (SCR) systems for diesel vehicles the injected urea solution decomposes to ammonia and isocyanic acid (HNCO), which reacts with water to another ammonia molecule and carbon dioxide over the SCR catalyst or a special urea decomposition catalyst. The second reaction step, i.e. the catalytic hydrolysis of HNCO was studied on the anatase TiO$_{2}$(101) surface and Al$_{2}$O$_{3}$(100) surface with ab initio density functional theory (DFT) calculations using a cluster model as well as with in situ diffuse reflectance infrared Fourier transform spectra (DRIFTS) investigations and kinetic experiments. The following mechanistic pathway has been identified to be most feasible: HNCO dissociatively adsorbs on the metal oxide surface as isocyanates, which are attacked by water, thereby forming carbamic acid at the surface. In a further step this intermediate is transformed to a carbamate complex, which leads to CO$_{2}$ desorption and consequently NH$_{3}$ formation. The comparison between the sum of the theoretical vibrational spectra of the reaction intermediates with the in situ DRIFT spectra also strongly supports the accuracy of the second reaction pathway. This mechanism holds also for the HNCO hydrolysis over γ-Al$_{2}$O$_{3}$ and the reactivity compared to TiO$_{2}$ was found to be consistent with the heights of the barriers in the energy diagrams. Based on these promising preliminary results a computational screening has been started in order to predict the most active metal oxides and surfaces for this reaction.
Starting Page	1740
Ending Page	1745
Page Count	6
File Format	PDF
ISSN	10225528
Journal	Topics in Catalysis
Volume Number	52
Issue Number	13-20
e-ISSN	15729028
Language	English
Publisher	Springer US
Publisher Date	2009-07-10
Publisher Place	Boston
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Titanium dioxide TiO$_{2}$(101) surface Aluminium oxide γ-Al$_{2}$O$_{3}$(100) DFT DRIFTS Cluster model Isocyanic acid Carbamic acid Carbamate group Characterization and Evaluation of Materials Industrial Chemistry/Chemical Engineering Pharmacy Physical Chemistry Catalysis
Content Type	Text
Resource Type	Article
Subject	Chemistry Catalysis

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