Motoyasu Imamura

INNER-SHELL EXCITATION AND SITE SPECIFIC FRAGMENTATION OF POLY(METHYLMETHACRYLATE) THIN FILM

Soft x‐ray excitations in the 250–600 eV photon energy range on poly(methylmethacrylate) (PMMA) result in ionic fragmentation of the original polymer with the most intense ions corresponding to CH+3, H+, CH+2, CH+, CHO+, and COOCH+3. The photon energy dependence of ion desorption from thin films of PMMA was measured to investigate the primary steps in radiation induced decomposition following carbon and oxygen 1s electron excitations using monochromatic pulsed‐synchrotron radiation. It was clearly found that the decomposition depends on the nature of the electronic states created in the excited species. The fragmentation pattern changes depending on the transitions of the 1s electron to a Rydberg orbital, an unoccupied molecular orbital or the ionization continuum. Moreover, the fragmentation occurs specifically around the site of the atom where the optical excitation takes place. Excitations from carbon and oxygen 1s to σ* states seem to be specially efficient for ion production as observed in the case o...

Modification of structural and acidic properties of sol–gel-prepared alumina powders by changing the hydrolysis ratio

The structural and acidic properties of sol–gel prepared alumina powders as catalyst supports were modified by adjusting the hydrolysis ratio, R (i.e. molar ratio of water relative to the alumina precursor, R=[H2O]/[aluminium-tri-sec-butoxide (ASB)]). Structural properties (e.g. porosity) and acidic properties were measured for alumina powders prepared with various R values, from 3 to 13. For R 10, first-order particles were closely packed with ink-bottle-type pore structures, whereas for R=9 or 10, first-order particles were loosely packed with a spatial fractal arrangement that yielded pseudo-cylindrical pore structures. In addition, the alumina powders prepared with R=9 or 10 had larger water pore volume and stronger acidity than those with other R values. These properties unique to the powders prepared with R=9 or 10 were ascribed to relatively short Al–O–Al chain lengths that resulted in loose packing of first-order particles. The results here indicate that alumina powders with favorable properties as catalyst supports (e.g. mean pore diameter) can be tailored by selecting the appropriate R in the sol–gel synthesis process.

Structural changes of Y zeolites during ion exchange treatment: effects of Si/Al ratio of the starting NaY

Abstract The effects of Si/Al ratio of starting NaY zeolites on structural changes during ion exchange treatments were studied. Three zeolites of different Si/Al ratio were subjected to three cycles of ion exchange treatment using (NH 4 ) 2 SO 4 and subsequent calcinations, and analyzed after each cycle. In the first ion exchange, the structural changes of the zeolites were almost independent of the Si/Al ratio of the starting NaY zeolites. For all three zeolites, about 60% of Na ions were exchanged, and the relative crystallinity decreased to about 80% of the starting NaY. In the second and third ion exchanges, the structural changes depended on the Si/Al ratio of the starting NaY zeolites. The zeolitic framework of Y zeolite with a low Si/Al ratio of 2.4 deteriorated, whereas Y zeolite with a medium Si/Al ratio of 2.8 and Y zeolite with a high Si/Al ratio of 4.1 retained their high crystallinity even after the third ion exchange. Furthermore, among the three zeolites, Y zeolite with a medium Si/Al ratio of 2.8 showed largest degrees of ion exchange, dealumination, and mesopore formation.

Preparation of nickel-tungstate catalysts by a novel impregnation method

Abstract Nickel-tungstate/γ-alumina (NiW) catalysts were prepared by an incipient wetness impregnation method using citric acid as a complexing agent. Citric acid has been used by our research group in preparing cobalt-molybdate and nickel -molybdate catalysts. The extended X-ray absorption fine structure (EXAFS) data of the impregnating solutions indicated that citric acid contributes to the formation of polytungstate anions that are smaller than the dodecatungstate ions formed when conventional ammoniacal solutions are used. Sulfided NiW catalysts prepared by using citric acid showed higher hydrogenation activity and hydrogenation selectivity than NiW catalysts prepared using the conventional ammoniacal solutions.

EXAFS study on Pd–Pt catalyst supported on USY zeolite

Abstract Local structure around Pd and Pt in the bimetallic Pd–Pt catalysts supported on ultra stable Y (USY) zeolite (SiO2/Al2O3=680) was investigated by an extended X-ray absorption fine structure (EXAFS) method during oxidation, reduction, and sulfidation. The Pt L III-edge EXAFS spectra showed that a new bond that was significantly different from Pt–Pt to Pt–Pd metallic bonds was formed in the bimetallic Pd–Pt (4:1) reduced catalysts supported on USY zeolite. This new bond may reflect the ionic properties of Pt through the Pt–Pd interaction. Furthermore this new bond survived sulfidation indicating that the bond has a cationic property and sulfur-tolerance property. The Pt–Pd ionic interaction in these catalysts allows some of the Pd metal to survive as metallic phase. The existence of this metallic phase under sulfidation condition may result in high activity of Pd–Pt (4:1) catalyst supported on USY zeolite in the aromatics hydrogenation.

Hydrogenation of tetralin over sulfided nickel-tungstate/alumina and nickel-molybdate/alumina catalysts

Abstract Nickel-tungstate/alumina (NiW/Al2O3) and nickel-molybdate/alumina ( NiMo Al 2 O 3 ) catalysts were prepared using an incipient wetness impregnation method with citric acid as a complexing agent. The hydrogenation activity of both sulfided catalysts was measured in a continuous-flow reactor as well as in a batch tube-bomb reactor with tetralin as an aromatic compound. Activity and stability of both sulfided catalysts were then compared in detail. The hydrogenation activity of the two catalysts depended on the partial pressure of the hydrogen sulfide (H2S) in the reaction atmosphere, where dimethyl disulfide (DMDS) was added to control its pressure. The sulfided NiW/Al2O3 catalyst was advantageous in hydrogenating tetralin under low H2S partial pressure, and the structure of the sulfide phases was quite stable in the reducing atmosphere which was measured by XPS and EXAFS methods. On the other hand, the sulfided NiMo Al 2 O 3 catalyst was advantageous in hydrogenating tetralin under high H2S partial pressure, where the hydrogenation activity of both catalysts were inhibited by H2S. The sulfided NiMo Al 2 O 3 catalyst under low H2S partial pressure was less stable than the sulfided NiW/Al2O3 catalyst due to structural changes of the active phases, such as migration of the Ni species into γ-Al2O3 to form the NiAl2O4 phase and sintering of the MoS2-like phase as confirmed by an XPS and an EXAFS. The superiority of the sulfided NiW/Al2O3 catalyst over the sulfided NiMo Al 2 O 3 catalyst was indicated in deep hydrogenation of low-sulfur feedstocks.

Depth profiling of surface oxidized TiAlN film by synchrotron radiation excited X-ray photoelectron spectroscopy

Abstract Depth profiling analysis of the surface oxide layer of Ti 0.55 Al 0.45 N film was performed by means of synchrotron radiation excited X-ray photoelectron spectroscopy (SR-XPS). The results indicated that the oxidation of nitride and segregation into TiO 2 and Al 2 O 3 occur simultaneously and that the Al 2 O 3 layer is formed at the upper surface layer of the film. The depth profile of nitrogen species indicated that molecular N 2 which was formed by the oxidation of the nitride occurred only in the TiO 2 matrix. This implied that the surface Al 2 O 3 layer functions as a surface protective layer for not only the inward diffusion of oxygen but also the outward diffusion of molecular N 2 .

EXAFS study on the dispersion of molybdenum sulfide catalysts on γ-A12O3

The dispersion of molybdenum sulfide catalysts was characterized based on the lateral dimensions of MoS2 crystallites estimated by EXAFS. A new index ofN(Mo)/N(S), instead ofN(Mo), was used to estimate the average MoS2 size to minimize the contribution of the coexisting oxide or oxisulfide phase in the catalysts. EXAFS showed some advantages over other techniques, such as TEM or XPS.

In situ XAFS analysis system for high-pressure catalytic reactions and its application to CO2 hydrogenation over a Rh/Y-zeolite catalyst

An in-situ XAFS cell was developed and used for the structural analysis of a Rh ion-exchanged zeolite catalyst during high-pressure hydrogenation of carbon dioxide. The in-situ cell enabled analyses of the catalyst structures that changed with the reaction atmosphere and elapsed time; the peak assigned to Rh-O scattering changed to that assigned to Rh-Rh scattering at 404 K during the pretreatment by hydrogen. After 30 min. of the carbon dioxide hydrogenation reaction, the peak intensity assigned to Rh-Rh scattering increased corresponding to the increase in the catalytic activity.

XPS depth profiling by changing incident X-ray energy

Abstract Excitation energy variable XPS measurements were performed using high-flux soft X-rays from synchrotron radiation. This method enables non-destructive XPS depth profiling by changing the photoelectron attenuation length. In the analysis of a HF cleaned silicon wafer, the present method revealed the presence of a very thin (∼ 1A˚) surface layer of partially oxidized silicon (Siδ+) which would not be detected by conventional Al or Mg Kα X-ray sources.