| Due to the development of modern industry, various nitrogen oxides have become one of the most crucial gases to our environment. Therefore how to clear up NOx has been an extremely concerned project for various countries.In this work location of Cu+in Cu-ZSM-5 was studied using density functional theory method with a 22T model containing the straight and sinusoidal channels as well as the channel intersection of ZSM-5. It was found that Cu+is stabilized in ZSM-5 by forming two or three Cu-0 bonds with the zeolite framework oxygen atoms. Three stable sites were identified for Cu+in the ZSM-5 framework, i.e.; in the straight channel (type I site), in the sinusoidal channel (type III site) and in the intersection region of these two channels (type II site).The adsorption of NOx molecules (NO, N2O, NO2) in different Cu+sites of Cu-ZSM-5 showed that the molecules acquired negative charges, indicating aπback donation of d electrons of Cu+toπ* antibonding orbital of the adsorbed molecules. The optimization of the adsorption complexes of NO and NO2 on type I and III Cu+ sites reached the same equilibrium geometry. Among the three Cu+sites, NOx molecules are most negatively charged in the complexes involving type II site, which indicates that the molecules are most significantly activated on this site, and therefore the catalytic reaction might occur in the intersection region of ZSM-5.Based on this, the produce and decomposition of NOx molecules on the Cu+ center of the intersection region of Cu-ZSM-5 was investigated in details, and the catalytic reaction cycle of NOx was determined. It was found that the initial step of the reaction is that NO adsobed on the Cu+site and decomposed to adsorobed 0 (S*O) and N2O. The following decompsition of the adsorbed N2O has two possible ways:1) reacts with S*O to produce N2+O2; 2) decompses to N2 and adsorbed O, and then the adsorbed O could reaction with the new adsorbed NO to produce NO2. NO2 was then decomposed to complete the reaction cycle. |
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