Lee Deuk Ki
Division of Civil and Environmental Engineering, Gwangju University, Gwangju 503-703, Korea.
Environ Sci Technol. 2003 Dec 15;37(24):5745-9. doi: 10.1021/es034332q.
Aqueous phase catalytic oxidation of ammonia has been studied over Ru/TiO2 catalyst in a batch reactor by changing the solution pH, concentration of catalyst in the solution, temperature, and reaction time. The oxidation reaction of ammonia over Ru/TiO2 catalyst has been found to take place exclusively for the aqueous NH3 with a preferred mode in strong alkaline pH region. An oxidation reaction pathway has been proposed as follows: Oxidation of ammonia is initiated by the reaction of aqueous ammonia with catalytically activated oxygen. After undergoing further successive oxidation reactions with activated oxygen, ammonia is finally oxidized to a molecule of nitrous acid. Nitrous acid dissociates into a nitrite ion and a proton. The solution pH is decreased with the protons from the dissociation of HNO2 so that the solution concentration of NH4+ is increased. Molecular nitrogen as a final product is produced from the homogeneous aqueous phase reaction between nitrous ion and ammonium ion. Further reaction of nitrous ion with the activated oxygen leads to the formation of nitrate ion. The reaction pathway proposed has been validated with the changes of solution pH along with the ammonia conversions, and the formation of N2 from the solution containing NO2- and NH4+ ions in equimolar amounts of nitrogen has been confirmed in a separate experiment. The kinetics of aqueous ammonia oxidation reaction has been well represented as a first-order reaction with respect to the concentration of aqueous ammonia, and an apparent rate constant has been obtained as a function of catalyst concentration in solution, oxygen pressure, and reaction temperature.
通过改变溶液pH值、溶液中催化剂的浓度、温度和反应时间，在间歇式反应器中研究了Ru/TiO₂催化剂上氨的水相催化氧化。已发现Ru/TiO₂催化剂上氨的氧化反应仅针对水溶液中的NH₃发生，且在强碱性pH区域具有优先模式。提出了如下氧化反应途径：氨的氧化由水溶液中的氨与催化活化的氧反应引发。与活化氧进一步连续发生氧化反应后，氨最终被氧化为一分子亚硝酸。亚硝酸解离为亚硝酸根离子和质子。随着HNO₂解离产生的质子使溶液pH值降低，从而使NH₄⁺的溶液浓度增加。亚硝酸根离子与铵离子之间的均相水相反应产生分子氮作为最终产物。亚硝酸根离子与活化氧的进一步反应导致硝酸根离子的形成。所提出的反应途径已通过溶液pH值随氨转化率的变化得到验证，并且在单独的实验中已证实等摩尔量的含NO₂⁻和NH₄⁺离子的溶液中形成了N₂。氨的水相氧化反应动力学很好地表现为相对于氨水溶液浓度的一级反应，并获得了作为溶液中催化剂浓度、氧分压和反应温度函数的表观速率常数。
