Nobuyuki Matsubayashi

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.

XANES and EXAFS analysis of copper ion-exchanged ZSM-5 zeolite catalyst used for nitrogen monoxide decomposition

XANES and EXAFS analysis of Cu ion-exchanged ZSM-5 zeolite, a highly active catalyst for NO decomposition, is performed. The copper species in the zeolite are Cu(II) ions in the zeolite cages. The contribution of Cu-Cu local structure is suggested for high loading samples. The Cu atoms in the zeolite are more ionic than CuO. The analysis of the catalyst deactivated by SOx treatment suggests the presence of Cu atoms surrounded by SO4 ions which blocks the adsorption of NO molecules.

Confirmation of sulfur tolerance of bimetallic Pd–Pt supported on highly acidic USY zeolite by EXAFS

The sulfur tolerance (i.e., degree of sulfidation) of Pd and Pt in sulfided bimetallic Pd–Pt catalysts (Pd : Pt mole ratio of 4 : 1) supported on USY (ultrastable Y) zeolites (SiO2/Al2O3 = 10.7, 48, and 310) was investigated using an extended X‐ray absorption fine structure (EXAFS) method. The sulfidation of the catalysts was done in a 1000 ppm H2S–2% H2/N2 stream at 573 K for 0.5 h. In the Fourier transforms of Pd K‐edge and Pt LIII‐edge EXAFS spectra, both of the peaks due to metallic Pd and to metallic Pt for the Pd–Pt/USY (SiO2/Al2O3 = 10.7) catalyst remained most after sulfidation. Further, the results of the Fourier transforms confirmed that the sulfur tolerance of both Pd and Pt decreased with increasing SiO2/Al2O3 ratio, suggesting that Pd and Pt become sulfur‐tolerant when Pd–Pt bimetallic particles are supported on highly acidic USY zeolite.

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.

Molybdate catalysts prepared by a novel impregnation method: Effect of citric acid as a ligand on the catalytic activities

Abstract Molybdate, nickel-molybdate and cobalt-molybdate/γ-alumina catalysts were prepared by an impregnation method using citric acid as well as ammonia as ligands. Molybdenum structures in the impregnating solutions and on the sulfided catalysts were characterized by EXAFS and XPS. Agglomerated molybdenum octahedra existed in the impregnating solutions containing citric acid, in contrast to the monomeric molybdenum tetrahedra obtained when using ammonia. The nickel-molybdenum catalyst prepared by using citric acid was inferior to the one prepared by using ammonia in terms of both hydrogenation and HDN activities, which might be due to a decrease in the amount of active Ni-Mo-S phase. On the other hand, the cobalt-molybdenum catalyst prepared using citric acid was superior to the one prepared using ammonia in terms of HDS activity. A decrease in the lateral size of MoS2-like crystallites might attribute to an increase in the HDS activity.

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.

Influences of oxygen-containing substances on deactivation of sulfided molybdate catalysts

Abstract The influences of oxygen-containing compounds on the changes in chemical states of sulfided metals in molybdate catalysts during the hydrotreatment of hydrocarbon feedstocks were investigated. The effect of oxygen-containing model compounds on the deactivation in the hydrodenitrogenation (HDN) activity of Ni Mo catalyst in hydrotreating a subbituminous coal-derived kerosine oil was in the order of O2 H2O2 > benzofuran > phenol > H2O. The XPS analyses of the heavily deactivated Ni Mo catalysts in the presence of oxygen-containing model compounds showed that the amounts of Mo4+ decreased significantly, and almost all of nickel sulfide and sulfidic sulfur were converted into Ni2+ and sulfate sulfur, respectively. The pre-oxidation of the sulfided Ni Mo catalyst via air, i.e. the formation of metal sulfides into oxides/sulfates, resulted in a decrease in HDN activity. The higher the degree of oxidation was, the lower the HDN activity was. It was suggested that some amounts of metal sulfides were converted into the lower reactive oxides/sulfates via oxygen in the oxygen-containing compounds even under hydrotreating conditions.

EXAFS analysis of vanadium oxide thin overlayers on silica prepared by chemical vapour deposition

The structure of vanadium oxide overlayers of V2O5/SiO2 catalysts prepared by chemical vapour deposition (CVD) and impregnation methods has been determined by using vanadium K-edge EXAFS and XANES. The Fourier transform of EXAFS for the vanadium oxide overlayers obtained by CVD of VO(OC2H5)3 showed very weak peaks due to V—O—V bonds, even at the high loading level of V2O5(17 wt.%), while crystalline V2O5 gave strong peaks due to V—O and V—O—V bonds. On the basis of the EXAFS and XANES results, it has been concluded that the vanadium oxides obtained by the CVD method were present as thin overlayers on SiO2, and were stable to calcination at 773 K. On the other hand, with an impregnation method, XANES of V2O5/SiO2 at loading levels less than 5 wt.% gave peaks different from those of crystalline V2O5. It was presumed that an isolated V species was formed as reported in the literature. At loading levels >5 wt.%, XANES and EXAFS for V2O5/SiO2 catalysts prepared by the impregnation method were very similar to those of crystalline V2O5, indicating that crystallites of V2O5were formed on SiO2 in this case. This occurs because aggregates of vanadium compounds, e.g. oxalate, were formed as precursors of V2O5 during the drying process.