| In order to meet the increasingly strict regulations on emission of vehicle exhausts, NH3selective catalytic reduction (NH3-SCR) de-NOx technology has become a hot research. At present, SCR catalysts include noble catalysts, oxide catalysts and zeolite catalysts. With wide activity temperature window, excellent hydrothermal stability and high N2selectivity, Cu/SAPO-34becomes a promising new NH3-SCR catalyst.To investigate the adsorption properties and roles of NH3and NOx in NH3-SCR process, the adsorption sites, strength, amounts and rates of NH3and NOx on Cu/SAPO-34catalyst were studied in this work. In additional, the reaction mechanisms were discussed.Cu/SAPO-34catalyst was prepared through ion exchange method by H-SAPO-34powder with determine ratio of Al/Si/P. We analysed the physical structure of H/Cu-SAPO-34zeolites through ICP-AES, XRD and ex situ DRIFT. The introduction of Cu ions did not destroy the chabazite zeolite structure of SAPO-34, and copper ions were well-dispersed or existed as isolated ions at the exchange sites.Transient response experiments showed that NH3was adsorption gas, while NOx were not. H-SAPO-34contains a large number of Br nsted acid sites and Lewis acid sites, which can adsorb and store a lot of NH3species. As Lewis acid sites, Cu cations can also adsorb NH3molecures, but they occupy more other adsorption sites. So the total amounts of NH3are less than that of H-SAPO-34. Cu species can promote the oxidization of NO and stored on Cu sites as nitrates/nitrites.In order to investigate the surface reaction mechanism, the roles of adsorbed species on different adsorption sites were studied. As active sites, the NH3adsorbed on Cu2+cations can take part in SCR reaction directly, and the NH3species adsorbed on other sites can migrate to Cu2+cations to react indirectly.NH3-Cu2+would react with the nitrites/nitrates stored on Cu ions to form intermediate species, NH4NO2and NH4NO3. Finally, the intermediate species decomposed into N2, H2O and little N2O. |
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