Selective Catalytic Reduction Of NO By Ammonia Over Pt/Fe/Cu Al-Rich Beta Zeolite

Nitrogen oxides are common atmospheric pollutants, which lead to acid rain and photochemical smog, and they can cause a series of significant environmental issues. How to remove nitrogen oxides effectively has become an important topic in today's environmental protection. This thesis aims at the disadvantage that the commercial NH3-SCR catalyst shows low activity at lower temperatures, and uses aluminum-rich Beta zeolite (Si/Al?4) from organotemplate-free synthesis as the support. By loading Fe and Cu ions, NH3-SCR catalysts with excellent performance have been prepared. The influences of the reaction conditions and Pt modifications on the NH3-SCR catalysts have been investigated in the presence of H2O, CO2 and C3H6. The main results are as follows:Cu-Beta-4 catalyst was prepared by ion-exchange of Al-rich Beta zeolite with Cu2+ Cu-Beta-4 has an excellent catalytic performance not only under standard NH3-SCR conditions but also under conditions of H2O, CO2 and C3H6. The activity of NH3-SCR decreases in the low and middle temperature window as a result of the existence of C3H6. When H2O, CO2 and C3H6 exist simultaneously, the poisoning effect of C3H6 can be inhibited in NH3-SCR. The deactivation of Cu-Beta-4 catalyst in the presence of C3H6 may be caused by the coke as revealed by the TG and 13C MAS NMR characterizations.Fe-Beta-4 and Fe-Cu-Beta-4 catalysts were prepared by impregnation of Al-rich Beta with Fe3+ or Fe3+/Cu2+, respectively. NH3-SCR performances were tested under different conditions. The presence of propylene can result in an obvious decrease in NH3-SCR activity of the Fe-Beta-4 in the whole temperature window, and the Fe-Cu-Beta-4 shows a similar trend. This may be caused by the competitive adsorption of propylene. When H2O, CO2, C3H6 coexisted, it could not significantly inhibit the poisoning effect of propylene to NH3-SCR.Based on Cu-Beta-4, we further prepared a series of Pt modified Cu-Beta-4 by impregnation, and the NH3-SCR performances were tested when H2O, CO2, C3H6 coexisted. It is found that the presence of Pt may improve the NO conversion and reduce the impact of C3H6 at lower reaction temperatures. But at higher reaction temperatures, the violent NH3 oxidation may result in insufficient reducing agent and decreased the NO conversion. This may be due to two reasons:firstly, Pt itself could serve as the active center in the oxidation of NH3, secondly, the introduction of Pt may transform part of the isolated copper ions into the clustered copper ions which are also the active center in the NH3 oxidation. Similarly, on Pt-Fe-Beta-4 and Pt-Fe-Cu-Beta-4, the decrease of NH3-SCR activities may also caused by the severe NH3 oxidation at higher temperatures.