Decomposition of Urea in the SCR Process: Combination of DFT Calculations and Experimental Results on the Catalytic Hydrolysis of Isocyanic Acid on TiO2 and Al2O3

被引:0
作者
Izabela Czekaj
Oliver Kröcher
机构
[1] Paul Scherrer Institute,Department General Energy
来源
Topics in Catalysis | 2009年 / 52卷
关键词
Titanium dioxide; TiO; (101) surface; Aluminium oxide; γ-Al; O; (100); DFT; DRIFTS; Cluster model; Isocyanic acid; Carbamic acid; Carbamate group;
D O I
暂无
中图分类号
学科分类号
摘要
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 TiO2(101) surface and Al2O3(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 CO2 desorption and consequently NH3 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-Al2O3 and the reactivity compared to TiO2 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.
引用
收藏
页码:1740 / 1745
页数:5
相关论文
共 106 条
[1]  
Piazzesi G(2006)undefined Appl Catal B 65 55-80
[2]  
Kröcher O(2000)undefined Ind Eng Chem Res 39 4120-173
[3]  
Elsener M(1982)undefined Chem Soc Rev 11 41-68
[4]  
Wokaun A(1996)undefined Combust Sci Technol 121 85-9366
[5]  
Kleemann M(1998)undefined Appl Catal B 18 1-630
[6]  
Elsener M(2007)undefined Catal Lett 115 33-320
[7]  
Koebel M(2001)undefined Surf Sci 490 116-175
[8]  
Wokaun A(1996)undefined Chem Soc Rev 25 61-undefined
[9]  
Belson DJ(1972)undefined Spectrosc Lett 5 477-undefined
[10]  
Strachan AN(1990)undefined Appl Catal 64 243-undefined