Extended X-ray absorption fine structure

About: Extended X-ray absorption fine structure is a research topic. Over the lifetime, 10452 publications have been published within this topic receiving 276744 citations.

Absorption Coefficients of Water Vapor in the Vacuum Ultraviolet

Abstract: Absorption coefficients of water vapor in the region 1060–1860A were obtained by a photoelectric method described previously. Pressures (0.08 to 8 mm Hg) of water vapor in the absorption cell were measured with an Alphatron gauge. In the region 1860–1500A, the absorption coefficients were between the values reported by two groups of investigators. Oscillator strengths of two continua, 1150–1430A and 1430–1860A, were found to be 0.05 and 0.041, respectively. At Lyman alpha the absorption coefficient was 387 cm−1. Twelve weak diffuse bands forming a progression in the region 1250–1450 and a number of bands in the region 1060–1250 were observed. The absorption coefficients of the continua and bands were independent of pressure, except for some of the bands in the region 1060–1250A.

Bis(μ-oxo)dicopper in Cu-ZSM-5 and Its Role in the Decomposition of NO: A Combined in Situ XAFS, UV−Vis−Near-IR, and Kinetic Study

Abstract: In situ XAFS combined with UV−vis−near-IR spectroscopy are used to identify the active site in copper-loaded ZSM-5 responsible for the catalytic decomposition of NO. Cu−ZSM-5 was probed with in situ XAFS (i) after O2 activation and (ii) while catalyzing the direct decomposition of NO into N2 and O2. A careful R-space fitting of the Cu K-edge EXAFS data is presented, including the use of different k-weightings and the analysis of the individual coordination shells. For the O2-activated overexchanged Cu−ZSM-5 sample a Cu···Cu contribution at 2.87 A with a coordination number of 1 is found. The corresponding UV−vis−near-IR spectrum is characterized by an intense absorption band at 22 700 cm-1 and a relatively weaker band at 30 000 cm-1, while no corresponding EPR signal is detected. Comparison of these data with the large databank of well-characterized copper centers in enzymes and synthetic model complexes leads to the identification of the bis(μ-oxo)dicopper core, i.e. [Cu2(μ-O)2]2+. After dehydration in H...

Formation of Ce1-xPdxO2-δ solid solution in combustion-synthesized Pd/CeO2 catalyst: XRD, XPS, and EXAFS investigation

Abstract: Pd/CeO2 (1 at. %) prepared by the solution-combustion method shows a higher catalytic activity for CO oxidation and NO reduction than Pd metal, PdO, and Pd dispersed over CeO2 by the conventional method. To understand the higher catalytic properties, the structure of 1 at. % Pd/CeO2 catalyst material has been investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and extended X-ray absorption fine structure (EXAFS) spectroscopy. The diffraction lines corresponding to Pd or PdO are not observed in the high-resolution XRD pattern of 1 at. % Pd/CeO2. The structure of 1 at. % Pd/CeO2 could be refined for the composition of Ce0.99Pd0.01O1.90 in the fluorite structure with 5% oxide ion vacancy. Pd(3d) peaks in the XPS in I at. % Pd/CeO2 are shifted by 3 eV indicating that Pd is in a highly ionic +2 state. EXAFS studies show the average coordination number of 3 around Pd2+ ion in the first shell of 1 at. % Pd/CeO2 at a distance of 2.02 Angstrom, instead of 4 as in PdO. The second shell at 2.72 Angstrom is due to Pd-Pd correlation which is larger than 2.69 Angstrom in PdO. The third shell at 3.31 Angstrom having 7 coordination is absent either in Pd metal or PdO, which can be attributed to -Pd2+-Ce4+- correlation. Thus, 1 at. % Pd/CeO2 forms the Ce1-xPdxO2-delta type of solid solution having -Pd2+-O-2-Ce4+- kinds of linkages.