Chapter 4 Characterization of Catalyst Structures by Extended X-Ray Absorption Spectroscopy

Abstract

This chapter presents the examples that illustrate the possibilities of the X-ray absorption spectroscopy (XAS) technique: with certainty that all atoms within reach of the exploring beam are detected—thus differing from other techniques such as ultraviolet (UV) or electron spin resonance (ESR)—and with complete selectivity for the element examined, the identity of the atoms neighbours to the latter (with an accuracy of a few Z units) and their number (with a moderate error) and the corresponding interatomic distances (with an accuracy of a few hundredths of A) can be determined. Besides that, some information about the electronic structure of the catalytic active species, and from it also about its symmetry characteristics, can be obtained from the structure of the absorption edge. The main pitfalls of the technique lie in the need of performing carefully the experiments and the data analysis, to avoid systematic errors and distortions of the data (especially in the calibrations and baseline subtractions) which could alter the meaning of the results. This point has been particularly stressed in the discussions held during the last International Conferences on extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES).