XAFS CHARACTERIZATION ON THE ACTIVE SITES OF Ni／γ—Al2O3 CATALYSTS FOR NO—SCR BY PROPENE

Ni/γ-Al2O3 catalysts show high catalytic activity for the selective catalytic reduction of NO by C3H6.The microstructures of nickel species were characterized by the spectroscopy of X-ray Absorption Near Edge Structures(XANES) and Extended X-ray Absorption Fine Structures(EXAFS).The resuts of XANES and EXAFS indicate that the nickel species in the sample calcined at 500℃mainly exist as highly dispersed NiO phase,Whereas in the samples calcined at750 and 950℃,the nickel species mainly exist as NiAl2O4-like spinel.The surace NiAl2O4-like spinel is the main active site for the selective reduction of No,and the highly dispersed NiO phase is the main active site for C3H6 oxidation. The formation of subsurface or buld NiAl2O4 spinel results in the reduction of surface spinel and cuases the decrease of activity for the selective catalytic reduction of NO by propene.