Hideto Sakane

Deterioration mechanism of Cu÷ZSM-5 as a catalyst of selective reduction of NOx by hydrocarbons from the exhaust of stationary natural gas-fuelled engine

The durability of Cu-ZSM5 as a catalyst of selective reduction of NOx by hydrocarbons from the exhaust of stationary natural gas engines was examined. Even 100% ion-exchanged Cu-ZSM5 also showed a deterioration tendency at 773 K under wet conditions simulating lean-burning gas engine exhaust. From the results of the durability test of SOx concentration dependence, SOx was not considered to be the cause of the deterioration. The deteriorated Cu-ZSM5 was characterized by the measurements of BET surface area, CO adsorption, XRD, NMR, EXAFS, XANES as well as carbon analysis. Neither dealumination, carbon deposition nor loss of micropore was observed in the deteriorated sample, and CuO cluster formation and resultant loss of surface area of copper were clearly shown, therefore, the CuO cluster formation is considered to lead to deterioration of the activity of Cu-ZSM5.

Structures of Fe(III) complexes with EDTA and EDDDA in aqueous solution by EXAFS and XANES

Abstract The Fe K-edge X-ray absorption spectra of Fe(III) complexes with EDTA (ethylenediaminetetraacetic acid) and EDDDA (ethylenediamine- N , N -diacetic- N , N ′-dipropionic acid) in weakly acidic or neutral aqueous solutions are measured. The spectra of powdered crystalline samples of these complexes are also measured as the reference materials. The comparisons of the XANES spectra, including their pre-edge peak, and the EXAFS Fourier transforms conclude that in aqueous solution a seven-coordinate structure is predominant for the Fe(III)-EDTA complex and a six-coordinate one for the Fe(III)-EDDDA complex.

Solvation structures for bromide ion in various solvents by extended X-ray absorption fine structure

The Br K-edge X-ray absorption spectra have been obtained for bromide ion dissolved in various protic and aprotic solvents. The Br ⋯ O distances in protic solvents which are fixed by the hydrogen-bond interaction and Br ⋯ C in aprotic solvents by the ion–dipole interaction were determined to be 3.1–3.2 and 3.5–3.6 A, respectively. The co-ordination numbers of Br– were found to be widely different, 3–6, from solvent to solvent. In protic solvents the solvation number correlates with the Mayer–Gutmann acceptor number, AN. Aprotic solvents can be divided into two groups in terms of the solvation structures. The solvation numbers in dimethylformamide, dimethylacetamide, dimethyl sulfoxide, acetone and ethyl methyl ketone are larger than those in other aprotic solvents possibly because of their bonding to Br–through two methyl groups. The amplitude of the extended X-ray absorption fine structure (EXAFS) oscillation evaluated from the peak intensity in the Fourier-transform spectrum correlates with AN throughout the series of solvents studied. This correlation is attributed to the similarity between the mechanism determining the amplitude of EXAFS and that of AN.

XAFS Studies of Copper/ Zeolite Catalysts for NOx Reduction

XANES and EXAFS of Cu ion-exchanged zeolite catalysts effective for selective reduction of NOx by hydrocarbons have been studied by using a laboratory EXAFS spectrometer. The structural change of Cu species during catalytic reaction is suggested from the changes of Cu-Cu interaction peaks in EXAFS Fourier transforms and of the peaks due to multiple scattering in XANES spectra. Copper ions before reaction exist as isolated ions at the ion-exchanging sites, while Cu atoms in deactivated catalyst are sintered to form cluster species.

Solvent effects on cobalt(III) and chromium(III) oxalato complexes by x-ray absorption fine structure

Abstract Cobalt and chromium K-edge XAFS (X-ray Absorption Fine Structure) spectra of [Co(ox)3[3−, [Co(ox)2]−, [Co(mal)2en]− and [Cr(ox)3]3− (ox = oxalate, mal = malonate, en = ethylenediamine) in solids and in various solvents were measured. XANES (X-ray Absorption Near-Edge-Structure) spectra of a trisoxolato cobalt complex, and a chromium complex, vary with the type of solvent, while such a solvent effect was not detected for [Co(ox)2en]− and [Co(mal)2en]−. EXAFS (Extended X-ray Absorption Fine Structure) analyses of the trisoxalato complexes in solvents indicate that metal-coordinating atom distances vary depending on the solvents used and linear reduction of the distances was observed with increasing Gutmanns acceptor number of a solvent. This trend is apparently in accord with the observed blue shifts in d-d absorption spectra of [Co(ox)3]− in greater acceptor number solvents. Furthermore, it was found that othr metal-ligand atom distances than interatomic distances of metal-directly coordinating atoms also shrink with acceptor numbers of solvents.

EXAFS and Ligand Exchange Reaction of Hydrated 3d Transition Metal Complexes

Relation between EXAFS parameters and ligand exchange reaction rate constant in solution is investigated. The EXAFS spectra of hydrated 3d metal complexes have been obtained over the temperature range of 20 K to 300 K. The temperature dependences of the mean square relative displacement σ2 and the third order coefficient C3 in cumulant expansion of EXAFS signal are examined for the first nearest metal-oxygen bond. The ligand exchange rate constant correlates not only with σ2 but also C3 both obtained from the EXAFS for solid hydrated complexes, and the higher the rate constant, the more rapidly σ2 and C3 increase with temperature.

Determination of dissociation energy for ligand exchange reaction from EXAFS.

EXAFS (extended X-ray absorption fine structure) experiments were performed at several different temperatures for a series of 3d transition metal ions (Cr3+, Fe3+, Fe2+, Ni2+, Co2+, Zn2+) in aqueous solutions. Anharmonic EXAFS analyses, which include up to third order cumulant, were carried out to study on the metal-oxygen bonding potential. According to the model in which the dissociation process is dominant for the ligand-water exchange reaction, the dissociation energy has been first evaluated from EXAFS in solution phase.

Anharmonic potential derived from EXAFS of hexaaqua transition metal complexes

EXAFS (extended X-ray absorption fine structure) experiments were performed at several different temperatures for a series of 3d transition metal ions (Cr3+, Fe3+, Fe2+, Ni2+, Co2+ and Zn2+) in aqueous solutions. Anharmonic EXAFS analyses, which include up to third order cumulant, were carried out to study the metal–oxygen bonding potential. According to the model in which the dissociation process is dominant for the ligand water exchange reaction, the dissociation energy has been evaluated by combining experimental results of temperature dependence of a harmonic Debye–Waller factor and an anharmonic third order cumulant for hydrated metal complexes. The dissociation energies deduced from the EXAFS experiments were found to correlate well with those having been theoretically predicted, and with the experimental water-exchange rate constants.

XAFS cumulant and ligand exchange reaction rate constant for metal ion in aqueous solution

Abstract The EXAFS spectra of hydrated transition metal complexes have been obtained for investigating the relation between the Debye-Waller factor, σ 2 , in EXAFS and the ligand exchange reaction rate constant, k 1 , for the complexes in aqueous solution. The relation between σ 2 and log k 1 is studied by use of the Arrhenius theory. The introduction of the anharmonic Morse function as the interaction potential is found to lead to a simple expression connecting them.