期刊
CATALYSIS SCIENCE & TECHNOLOGY
卷 3, 期 4, 页码 942-951出版社
ROYAL SOC CHEMISTRY
DOI: 10.1039/c2cy20668d
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资金
- TOTAL (France)
The catalytic hydrolysis of urea was investigated under conditions relevant for the selective catalytic reduction of NOx (urea-SCR). The hydrolysis activities of the tested catalysts coated on cordierite monoliths were in the order ZrO2 > TiO2 > Al2O3 > H-ZSM-5 > SiO2. A comparison with isocyanic acid (HNCO) hydrolysis on the same catalysts showed that urea decomposition was much slower than HNCO hydrolysis; hence, catalytic urea thermolysis into NH3 and HNCO is likely to be the rate-determining step in urea decomposition. Interestingly, a different order of catalyst activities was found in water-free experiments on urea thermolysis: TiO2 > H-ZSM-5 approximate to Al2O3 > ZrO2 > SiO2. The widely accepted reaction pathway for urea decomposition, namely urea thermolysis followed by HNCO hydrolysis, seems to be valid on all the tested catalysts except ZrO2: The high urea hydrolysis activity of the ZrO2 catalyst compared to its low urea thermolysis activity suggested a different reaction pathway, in which water directly attacks adsorbed urea rather than adsorbed HNCO.
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