NO adsorption on ZnAl2O4/Al2O3 powder: a NEXAFS study at the nitrogen K edge

In order to understand the mechanism of the selective catalysis of nitrogen oxide reduction by hydrocarbons on a ZnAl2O4/Al2O3 catalyst, the NO adsorp tion step has been studied as a function of the surface state of the cataly st by using near-edge X-ray absorption fine structure (NEXAFS) spectroscopy at the nitrogen K edge. The role of oxygen, whose presence is essential fo r the reaction to occur, is examined. In absence of a preliminary surface o xidation, nitric oxide was found not to be adsorbed on the ZnAl2O4/Al2O3 su rface. After this preliminary treatment, we observed that the nitrogen atom of the NO molecule was linked to a surface oxygen with an adsorption mode parallel or slightly tilted with respect to the catalyst surface. Through t hese experiments we clearly demonstrate the advantages of soft X-ray experi ments in catalysis research even in the case of practical application to re al materials.