| NH3-SCR is one of the most efficient technologies to decrease the NOx in theexhaust gas of stationary and mobile source. Cu/SAPO-34, owing to the excellenthydrothermal stability and superior SCR catalytic activity, has become the focus inzeolite catalysts. This paper is focused on the effect of synthesis method on thestructures and the Cu species of Cu/SAPO-34catalysts.In this paper, three Cu/SAPO-34catalysts were prepared by one-pot, precipitateand ion-exchange method respectively. To avoid the influence of Cu loading and thesupports on the SCR activities, all of the samples with the equivalent Cu loading andSi:Al:P ratio were achieved through the concise control. The NH3-SCR activity wasevaluated and various characterization methods (XRD, SEM, H2-TPR, EPR) wereused to probe the nature and structure of Cu species. Moreover, the kinetic study wasused to study the active sites over various Cu/SAPO-34catalysts. Finally, the effect ofsynthesis methods on the Cu species and the active sites was proposed.The results demonstrate that the synthetic method does not affect the structure ofthe catalyst, but affect the distribution of Cu species which leaing to the differentactivity of the SCR catalyst. The dominant Cu species is CuO-clusters forprecipitation sample, and it is isolated Cu2+for ion-exchange sample. Besides, bothCuO and Cu2+co-exist for one-pot catalyst. After hydrothermal treatment, the Cuspecies migrate from the external surface into the ion exchange sites and form moreisolated Cu2+species.The kinetic results demonstrate that the Cu/SAPO-34catalysts prepared bydifferent methods show the same activation energy (Ea=31.1±1.6KJ/mol) and TOFvalue. It proves that the SCR reaction routes are not changed and the active sites forthe NH3-SCR are the isolated Cu2+located on the ion-exchange sites at lowtemperature. The difference of SCR activity is caused by the various content ofisolated Cu2+over Cu/SAPO-34by different method. In addition, the Cu/SAPO-34prepared by one-pot method exhibits similar activity and hydrothermal durability asthe samples prepared by ion-exchange method. So the one-pot method is a promisingway to substitute for the ion-exchange method to synthesize Cu/SAPO-34. |
