Theoretical Study On Selective Catalytic Reduction Of Nitrogen Oxides In Hetero-Atom Mordenite

The removal of nitrogen oxides had become more and more important in the field of environmental protection. Zeolite could effectively eliminate NOx with the characteristic of high reaction activeness, high selectivity and wide reaction temperature range. mordenite was widely used as catalyst due to its high Si/Al ratio, high stability, good resistance to the water and acid. Therefore, the study on the selective catalytic reduction of nitrogen oxides in mordenite had great prospect in the field of catalysis. Mordenite was selected as catalyst in this paper. Adsorption properity and reaction mechanism of NOx in the hetero-atom mordenite were studied using quantum chemistry calculation.The models were constructed by B, Al, Ga or Fe replacing a Si atom at the T4 site. To maintain the charge neutrality of the whole system, a H+, Cu+ or Ag+ ion was incorporated. Then the models were optimizated. NH₃ was selected as alkaline probe molecular to examine its acidity. The results showed that the acidity of Al isomorphously substituted mordenite was strongest among the whole system.NOx, SO₂, H₂O, O₂, CH₄ and NH₃ molecules adsorption in Ag-[Al]MOR, Ag-[Fe]MOR Cu-[Al]MOR and Cu-[Fe]MOR were studied using quantum chemistry method. The results showed thatη1-N mode were more stable than inη1-O mode in these models. Ag-[Al]MOR and Ag-[Fe]MOR had certain ability to resist SO2, but not to be stable against H₂O poisoning. Both Cu-[Al]MOR and Cu-[Fe]MOR were plausible catalysts which were stable against water and SO2. Cu-[Fe]MOR was more stable than Cu-[Al]MOR.In addition, the reaction mechanism of NO decomposition in Ag-[Al]MOR was studied. Energy changes, transition states and activation energies were obtained. Rate-determining step and catalytic reaction paths were determined.