Hidenori Yahiro

An ESR study on the thermal electron excitation of a sodium atom incorporated in a silicon clathrate compound

Abstract An ESR study was carried out for sodium-containing silicon clathrate compounds, Na x Si 136 with 3 ⩽ × ⩽10. For Na 3 Si 136 a quartet with an isotropic hf splitting of 13.3 mT was observed together with the weak septet of 6.7 mT at 4 K; the former and the latter being attributed to the Na atom and the dimer cation Na 2 + , respectively. The temperature-dependent ESR spectral intensity of the Na atom was observed over a wide temperature range from 4 to 200 K. A deviation from the paramagnetic Curie law was observed in the higher temperature region and is discussed in terms of a thermal electron excitation from the Na impurity level to the conduction band of the silicon clathrate compound.

ESR study of the motional dynamics of NO2 adsorbed on Na-mordenite

Abstract The temperature dependent ESR spectra of NO 2 adsorbed on Na-mordenite have been studied in the temperature range 77–300 K. An analysis based on slow-motional ESR theory shows that the reversible change with temperature is caused by Heisenberg spin exchange. The activation energy is 0.8–1.6 kcal/mol depending on NO 2 concentration. The spin exchange is probably caused by the interaction of NO 2 molecules with each other as they diffuse along the channels of Na-mordenite.

ESR studies of nitrogen oxides adsorbed on zeolite catalysts:Analysis of motional dynamics

ESR spectra of NO2 adsorbed on X- and Y-type zeolites were observed in the temperature range 77–346 K. Based upon spectral simulation using a Brownian diffusion model, motional dynamics of NO2 adsorbed on zeolite surface were analyzed quantitatively. In the case of X-type zeolite, it was found that the ESR spectra below 100 K is near the rigid limit. Above 230 K, the average rotational correlation time decreased from 1.7×10−9 (230 K) to 7.5×10−10sec (325 K) with increasing temperature and its degree of anisotropy was very close to one (N=1.25). On the other hand, the temperature-dependent ESR spectra of NO2 adsorbed on Y-type zeolite were observed to be somewhat different from that for X-type zeolite.

ESR studies of the effect of zeolite structures on motional dynamics of NO2

Abstract Electron spin resonance (ESR) spectroscopy was used to study the effect of zeolite structure on the motional dynamics of NO 2 adsorbed on the zeolites. The temperature-dependent ESR spectral line shapes were quantitatively analyzed using the slow-motion ESR theory. It was observed that the motional dynamics of NO 2 is strongly dependent on the structure of the zeolite (Beta-type, ZSM-5, mordenite, L-type and ferrierite zeolites). The following important observations were made. (1) In zeolites with similar channel structures, the diffusion rate of NO 2 is proportional to the channel size, and the order of the diffusion rates is Beta-type>ZSM-5>ferrierite and L-type>mordenite. (2) The diffusion of NO 2 is faster in the zeolites with multi-dimensional channels (Beta-type, ZSM-5 and ferrierite) than that in those with uni-dimensional channels (L-type and mordenite).

EPR of silver–ammonia adducts in γ-irradiated AgNa-A zeolite with low silver content

An EPR study has been performed on a low Ag+-exchanged Na-A zeolite (Ag0.1Na11.9-A) on which ammonia had been adsorbed followed by exposure to γ-radiation at 77 K. The formation of Ag atoms, normally observed for zeolites with a high Ag content, is abated by the presence of ammonia. New EPR spectra with the silver hyperfine coupling constant slightly smaller than that of isolated silver atoms were observed. The new spectra were assigned to two silver–ammonia complexes, [Ag–NH3]0 and [Ag–(NH3)2]0, the former being more thermally stable than the latter; the latter decayed at 150 K. The EPR parameters of [Ag–NH3]0 were determined as follows: giso=2.005 and aiso(107Ag)=38.0, A⊥(14N)=1.4, A‖(14N)=1.7 and aiso(1H)≈0 mT. The formation reactions and possible locations of the adduct radical are discussed in terms of annealing temperatures and the amount of ammonia introduced.

An ESR study on reduction-oxidation properties of copper ions in Cu—Pd—H3PO4/SiO2 catalyst active in direct oxidation of benzene

The reduction-oxidation of copper ions in Cu—Pd—H3PO4/SiO2 catalysts, active in the direct oxidation of benzene to phenol, was studied by means of electron spin resonance spectroscopy. The isolated and aggregated copper (II) ions were found to exist on the Cu—Pd—H3PO4/SiO2 catalyst after evacuation at room temperature. A portion of the Cu(II) ions supported on SiO2, isolated Cu(II) ions coordinated with PO43−, was found to be reversible with alternate reduction-oxidation treatments at 200°C. When the ESR results were compared with the formation rates of phenol, the ‘reversible’ Cu(II) ions were concluded to be responsible for catalytically active sites.

14-P-09-EPR studies on nitrogen monoxide in zeolites

Publisher Summary This chapter presents electron paramagnetic resonance (EPR) studies on nitrogen monoxide (NO) in zeolites. NO introduced into sodium (Na)-A(Na-LTA), Na-mordenite(Na-MOR), and Na-ZSM-5(Na-MFI) zeolites is studied by X-band-EPR measurements. The EPR spectra of NO introduced into Na-LTA reveals the presence of two monoradicals with different rotational rates. The rotational motion of the NO monoradical formed in Na-LTA differs from that in Na-MOR and Na-MFI. A (NO)2 biradical is present in Na-LTA while it is absent in the calcium ion-exchanged A-type zeolite, indicating that the pressure of Na+ is essential for the (NO)2 biradical formation.

Reduction of poly(tetrafluoroethylene) by aromatic radical anions: An ESR and NMR study

An ESR and 19F-NMR study was carried out to elucidate the reduction kinetics of PTFE with aromatic radical anions (anthracene, benzophenone, biphenyl, and naphthalene), whose counter cation is Na+, in THF solvent. The ESR signal intensities of aromatic radical anions decayed according to the second-order equation whose rate depends on the kind of radical anions; the relative order being naphthalene (1.00) ≫ biphenyl (0.03) > anthracene (0.02) > benzophenone (0.003). The defluorination from PTFE was examined by a high-resolution 19F-NMR method of NaF disolved in an ethanol/water mixed solvent. When an excess amount of Na metal was present, the yield of NaF exceeded the initial concentration of aromatics. The result suggests that the aromatic radical anions are regenerated by the reaction with excess Na metal. The amounts of NaF salts produced during the reducing process were also followed by the same order as the decaying rates of aromatic radical anions.

Anode Performance of Ni/(CeO2)1-x(LnO1.5)x (Ln: Lanthanoids) in SOFCs Using Hydrocarbon Fuels

The anode performances of Ni/(CeO2)1-x(LnO1.5)x (Ln: La, Pr, Nd, Sm, Gd, and Yb) were investigated in direct-methane solid oxide fuel cells. Among the anodes tested in the present study, Ni/CeO2-Sm2O3 and Ni/CeO2-Yb2O3 composite anodes showed the relatively low anodic overpotential. The anodic overpotential of Ni(x wt%)/(CeO2)1-y(SmO1.5)y depended strongly on Ni content, while it less depended on Sm content. The catalytic activity of methane oxidation was measured for Ni/LnDC at 973 K and Ni/CeO2 and Ni/CeO2-Yb2O3 samples showed the high catalytic activity. This result suggests that the activity for the direct oxidation of methane by O2 is not main factor controlling the anodic overpotential in direct methane solid oxide fuel cell.