| Density function theory (DFT) has been applied to investigate theadsorption of NO and N2O on beta zeolite and the mechanism of N2Oreduction by CO. We also employ the Gambit software and FLUENT softwareto investigate the performances of transfer and reaction for SCR of N2Oremoval with CO in reactors of different shapes.Firstly, density function theory (DFT) has been applied to investigate theinteractions between NO and N2O with Cu+species in a beta zeolite (BEA) atsites T1and T9. The geometries for Cu-BEA represented as10T cluster, andcomplexes of NO and N2O adsorptions on them in η1-O and η1-N modes havebeen completely optimized. The calculated results showed that NOx could beadsorbed on Cu+species in two modes, and N-O bond distances of NOxincrease after adsorption, showing that NO is activated. The adsorptionenergies of NO and N2O molecules in η1-N mode on Cu-BEA are larger thanin η1-O mode, indicating that the configuration in η1-N mode is more stablethan in η1-O mode. The adsorption energy of N2O or NO molecule on Cu-BEAat site T9is larger than at site T1in both modes, showing that the interactionsbetween N2O or NO and Cu-BEA at site T9are stronger than at T1site. Secondly, density function theory (DFT) methods have been applied tothe investigation of the interaction of NO and N2O with [FeO]+species in abeta zeolite (BEA). The geometries for H-BEA and Fe-BEA represented as10T cluster, and NO and N2O adsorption on them in η1-O and η1-N modeshave been completely optimized. The adsorption energy of NO and N2Omolecule in η1-N mode on Fe-BEA and H-BEA is larger than that in η1-Omode, indicating that NO and N2O is mainly bonded by N to H or Fe atom.The adsorption energy of NO and N2O molecule on Fe-BEA is larger than thaton H-BEA, indicating that iron site is preferred. Adsorption energies for N2Oand NO follow the order of NO> N2O, predicating that the affinity of NOmolecule on BEA zeolite is much stronger than N2O molecule on BEA zeolite.Thirdly, this study is focused on nitrous oxide (N2O) decomposition bythe combination of experimental and theoretical methods. Fe-beta zeolite wasprepared by wet ion-exchange method, and their activity measurement indirect N2O decomposition and N2O reduction with carbon monoxide (CO)were carried out respectively. The experimental results showed that N2Oconversion is apparently improved in N2O decomposition by CO as reducingagent. Fourier Transform Infrared (FTIR) spectroscopy and density functiontheory (DFT) methods have been applied to the investigation of themechanism of N2O reduction by CO on Fe-modified beta zeolite. Thegeometries of Fe-beta zeolite and Cu-beta zeolite represented as5T cluster,reactants, transition states and products on two possible pathways have been completely optimized. We used the [FeO]+and Fe+as the active centers inFe-beta zeolite and Cu+as the active centers in Cu-beta zeolite. The pathway1includes two step (the N2O decomposition and the removal of active O atom),and pathway2has one step (adsorbed N2O and CO reacts). The result showsthat N2O decomposition by CO can easily occurs through the two pathways.On [FeO]+active site, activation of N2O with energy barrier of141.24kJ·mol-1is the main reaction step of pathway1, and the energy barrier ofpathway2is172.99kJ·mol-1. On Fe+active site, desorption of CO2withenergy barrier of38.22kJ·mol-1is the he main reaction step of pathway1, andthe energy barrier of pathway2is70.56kJ·mol-1. The result shows that thereaction may happen through the two pathways, and pathway1is dominant.The energy barrier on [FeO]+active site is larger than that on Fe+active site,O atom of [FeO]+active center could easily be removed by CO, and theenergy barrier (38.22kJ·mol-1) is very low, indicating that the active center inFe-beta zeolite may be Fe+species in N2O reduction by CO. The energybarrier on Cu+active site (pathway1(146.36kJ·mol-1) pathway2(166.39kJ·mol-1)) is higher than that on Fe+active site indicating that the activation onFe+active site is higher than that on Cu+active site. It was also found that COadsorbed on beta zeolite induces the fast removal of surface atomic oxygencoming from N2O molecule decomposition on Fe-beta zeolite. The adsorbedCO molecule can also easily react with adsorbed N2O molecule to formproducts because of the low energy barrier. Lastly, we tries to identify the relationship of monolith catalysts betweengeometric configuration and performances of transfer and reaction for SCR ofN2O removal with CO. Five kinds of channel shapes like round, regulartriangle, rectangle, square and hexagon, as well as traditional pelletpacked-bed reactor, were investigated to compare their momentum transfer(i.e. pressure drop P), heat transfer (i.e. Nu number), mass transfer (i.e. Shnumber) and reaction performance (i.e. N2O conversion). It was found thatpressure drop is in the order of pellet>> round> regular triangle> rectangular> square> hexagon. For monolith catalysts, Nu and Sh are in the order ofround> regular triangle> rectangular≈square> hexagon. However, fortraditional pellet packed-bed reactor, Nu and Sh have relation with the kind ofcarrier gas, but they are always larger than those of monolith catalysts whetherit is He or N2as carrier gas. N2O conversion finally depends on the mutualcontributions of reaction and transfer, and thus is in the order of pellet>>round> regular triangle> rectangular≈square> hexagon, whether it is N2orHe as carrier gas. The channel size also has influence on N2O conversion andpressure drop.
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