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 adsorption step has been studied as a function of the surface state of the catalyst by using near-edge X-ray absorption fine structure (NEXAFS) spectroscopy at the nitrogen K edge. The role of oxygen, whose presence is essential for the reaction to occur, is examined. In absence of a preliminary surface oxidation, nitric oxide was found not to be adsorbed on the ZnAl2O4/Al2O3 surface. 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 these experiments we clearly demonstrate the advantages of soft X-ray experiments in catalysis research even in the case of practical application to real materials.