Research On Preparation Of Modification Cu-ZSM-5 Catalysts And Its Removal Of NO

Cu-ZSM-5 is a kind of ideal catalyst for removal of NO in coal-fired gas since it can direct decomposition NO to N2 and O2. But it also has narrow temperature range, higher reaction temperature and obvious oxygen inhibition. This paper mainly studies how to improve the oxygen resistance of Cu-ZSM-5 and preparation of Cu-ZSM-5/CeYSZ composite membrane catalyst.In the preparation process of Cu-ZSM-5, the optimum concentration of Cu ion-exchange solution is 0.010mol/L and the temperature is 40℃. The amount of Cu loading in zeolites increases with the exchange times but the NO removal efficiency does not have apparent change. High temperature sintering can significantly improve the activity of the catalyst. Oxygen concentration has obviously impact on catalysts activity. The catalysts activity decreases when oxygen concentration reaches to 5% and becomes very low when oxygen concentration reaches to 10%.Introduction of co-ions and assistants can improve the resistance of catalysts to oxygen. Introduction of Ag+ and Ce3+ by ion-exchange can increase the activity of catalyst and reduce reaction temperature. The optimum ion-exchange sequence of Ag-Cu-ZSM-5 is loading Ag+ first, and then Cu2+, which the NO removal efficiency could reach 60% at 320℃within 5% of O2. Introduction of Ce to Cu-ZSM-5 catalyst, Ce3+and Cu2+should be loaded at the same time which the NO removal efficiency could reach 61% at 330℃within 5% of O2. The co-existence of Ce and La can strengthen the oxygen resistance and widen the activity temperature interval. The addition of CaH2(10%wt.) into Cu-Ce-La-ZSM-5 by blending can greatly promote the NO removal efficiency, which could reach 83% at 340℃within 5% of O2.The Cu-ZSM-5/CeYSZ composite membrane catalyst is prepared by sol-gel process through coating CeYSZ membrane and ZSM-5 membrane on Al2O3. Cu-ZSM-5/CeYSZ maintains constant activity about 65% when the concentration of O2 below 7% and the activity of catalysts sharply decrease when the concentration of O2 above 7%.The adsorption of nitrous oxide on Cu-ZSM-5 has been investigated using the ONIOM2 method. The analysis of frontier molecular orbital showed energy gap between Cu-ZSM-5 and nitrous oxide becomes smaller after introduction of Cu by ion-exchange. We can conclude from the thermodynamic data and adsorption structure of nitrogen oxides that N2O2 is the easiest adsorption form. The N-O bond length in N2O2 adsorption structure by Cu-ZSM-5 is longer than other structure. The calculated results also show that oxygen can easily adsorb by Cu-ZSM-5, so the existence of oxygen can restraint the adsorption of nitrogen oxides.