Mo／ZSM-5催化剂上NO催化还原反应机理与动力学研究

采用浸渍法制备了Mo/ZSM-5催化剂样品,并以氨为还原剂对其NO选择性催化还原活性、以及NO转化的反应速率进行测定.结果表明,在Mo/ZSM-5催化剂上不会发生NO氧化成NO2的反应,也没有N2O生成,然而有少量的NO分解反应发生.在氧气存在条件下,Mo/ZSM-5催化剂上NO-NH3-O2的SCR反应遵循LH机理.NO、O2和NH3首先吸附在Mo/ZSM-5表面,吸附态NO物种与吸附NH3物种直接反应生成氮气,气相氧的作用是加强NO吸附、补充催化剂表面吸附氧物种.并由此推导出NO转化的速率方程式,分别计算和模拟了在不同O2浓度、NO浓度和反应温度条件下NO的反应速率rNO值及其变化关系.结果表明,理论模拟值能够与实验值很好地吻合,所推测的机理能够很好地描述Mo-ZSM-5催化剂上NO选择性催化还原行为.

Kinetics and Mechanism of Catalytic Reduction of NO by NH3 over Mo/ZSM-5 Catalyst

The Mo/ZSM-5 catalyst was prepared by impregnation method.The activity of Mo/ZSM-5 catalysts for selective catalytic reduction of NO with ammonia and the rate of NO conversion were also measured.The results show that the oxidation of NO to NO2 did not occur in the reaction condition,N2O was not detected either.But a little amount of NO can be decomposed on Mo/ZSM-5 catalyst.According to experimental results the mechanism of NO-SCR in the presence of ammonia has been presumed as L-H model.The reactants NO,NH3 and O2 are first adsorbed on the surface of catalyst,then the adsorbed NO species reacted with adsorbed ammonia species on the surface to form N2 and H2O.The function of gaseous O2 is to enhance the adsorption of NO and addition of adsorbed oxygen species.From that an expression of rate of NO conversion was deduced,and the rNO value was calculated under the condition of different O2 concentration,NO concentration and reaction temperature respectively.The calculations show an high consistency with the experiment results,which means the presumed mechanism is suitable to the performance of Mo/ZSM-5 catalyst.