The Effect Of Si/P/Al Ratios To The SCR Activity Over Cu/SAPO-34Catalysts

The Selective Catalytic Reduction （SCR） is one of the most efficienttechnologies to decrease the NOx in the exhaust gas of stationary and mobile source.Compared with the noble catalysts, oxide catalysts and other zeolites catalysts theCu/SAPO-34is a promising candidate as NH₃-SCR catalysts. This paper is focusedon how the Si/P/Al ratios in support affect the structures and the activity ofCu/SAPO-34catalysts, aiming to find an appropriate support of Cu/SAPO-34catalysts and supply principles for researching and developing new zeolites SCRcatalysts.Three Cu/SAPO-34catalysts here with different Si/P/Al ratios were prepared bythe same ion-exchange method. The XRD,SEM,31P NMR,27Al NMR,29Si NMR wereused to research the effect of Si/P/Al ratios to the structures and acid density ofSAPO-34. Moreover, the H2-TPR,EPR,NH₃-TPD,NO-TPO and NH₃-TPO wereperformed to study the effect of Si/P/Al ratios to the acid density and the modes of Cuspecies on the Cu/SAPO-34catalysts. And the relation between the Si/P/Al ratios andthe SCR performance of different Cu/SAPO-34were concluded here.It is seen that the acid sites of SAPO-34origin from the substitution of P atomsin AlPOs by the Si atoms, so the acid density of SAPO-34increases with theimprovement of Si contents in supports. In addition, the Si and Al atoms inCu/SAPO-34are propitious to the loading of Cu in Cu/SAPO-34catalysts. There aretwo locations for Cu²⁺species in Cu/SAPO-34catalysts at least, and the Cu²⁺speciesin different sites show different SCR activity. Finally it is concluded that the differentSCR performance of three Cu/SAPO-34catalysts is caused by the acid content andthe modes of Cu species resulted by the various Si/P/Al ratios.The Cu/SAPO-34catalysts show good hydrothermal stability and the agedCu/SAPO-34samples perform as the same SCR activity as that of fresh samples,which is mainly for the good stability of support itself and the increase of Cu²⁺species, the active sites, in the aged Cu/SAPO-34catalysts.