Kinetics and Mechanism Study of Low-Temperature Selective Catalytic Reduction of NO with Urea Supported on Pitch-Based Spherical Activated Carbon

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• 作者：Zhi Wang ; Yanli Wang ; Donghui Long ; Isao Mochida ; Wenming Qiao ; Liang Zhan ; Xiaojun Liu ; Seong-Ho Yoon ; Licheng Ling
• 刊名：Industrial & Engineering Chemistry Research
• 出版年：2011
• 出版时间：May 18, 2011
• 年：2011
• 卷：50
• 期：10
• 页码：6017-6027
• 全文大小：1147K
• 年卷期：v.50,no.10(May 18, 2011)
• ISSN：1520-5045

文摘

The kinetics and mechanism of selective catalytic reduction (SCR) of NO with urea supported on pitch-based spherical activated carbons (PSACs) were studied at low temperatures. NO oxidation to NO₂ catalyzed by the 0.5鈭?.8 nm micropores in PSACs was found to be the rate-limiting step in urea鈭扴CR reaction, which was confirmed by both the apparent activation energy calculations and the kinetics results of urea鈭扴CR reaction and NO oxidation on PSAC. These two reactions gave very similar negative apparent activation energies (鈭?6.5 kJ/mol for urea鈭扴CR reaction and 鈭?5.2 kJ/mol for NO oxidation), indicating that the adsorption of reactants on PSAC is of key importance in these two reactions. Moreover, these two reactions were both approximately first-order with respect to NO and one-half order with respect to O₂. It was found that NO₃ from the disproportionation of the produced NO₂ was quickly reduced by supported urea into N₂. After the complete consumption of supported urea, NO₂ started to release, and the carbon surface was gradually oxidized by adsorbed NO_x species. NO₃ was found to be stably adsorbed on the oxidized carbon surface. On the basis of the results obtained, a reaction mechanism of low-temperature urea-SCR reaction on PSAC was proposed and discussed.