Applications of x-ray absorption fine structure (XAFS) spectroscopy in fuel science

摘要

X-ray absorption fine structure (XAFS) refers to the details ofnhow x-rays are absorbed by an atom at energies near and above thencore-level binding energies of that atom. XAFS spectra are especiallynsensitive to the formal oxidation state, coordination chemistry, andnthe distances, coordination number and species of the atomsnimmediately surrounding the selected element.1 Practically, XAFSncan be divided into two regions, near-edge region and extendednregion. The near-edge XAFS, or x-ray absorption near edge structuren(XANES), provides information on oxidation state, coordinationnsymmetry, and can be used for identification of different species bynfingerprinting. In contrast, extended XAFS, or EXAFS, measures thencoordination structure including bond distance and coordinationnnumber of neighboring atoms. XAFS has been applied in many fieldsnof research including fuel science. In this talk, two examples arengiven to illustrate the uniqueness of XAFS spectroscopy. In onenexample, catalyst deactivation in CeO2–Al2O3 supported Ni catalystsnfor hydrogen production from steam reforming of liquidnhydrocarbons in the presence of sulfur impurities was studied bynXANES for a better understanding of sulfur poisoning mechanism.nXANES spectroscopy at sulfur K-edge (2472 eV), and carbon Kedgen(284.2 eV) was used to identify the sulfur and carbon species innthe used catalysts and provided new insight into sulfur poisoningnmechanism in steam reforming catalysts.2-4 In the other example,nstructure of a PtNiFe/C cathode electrocatalyst used in PEM fuelncells was probed by EXAFS at Pt L3 edge (11,564 eV).