一國 伸之

We prepared Rh ion exchanged Y-type zeolite (RhY) and Li-doped RhY (Li/RhY) catalysts and studied the structure transformation of Rh intercalated species during CO adsorption and CO2 hydrogenation by EXAFS and TEM. We found that Rh particles in RhY initially supported inside the zeolite cage as 1.3 nm spherical or hemispherical particles. CO exposure of the fresh RhY caused formation of atomically dispersed Rh species. After CO2 hydrogenation and following reduction, the Rh particles aggregated to form 3.3 nm particles on the outer surface. Meanwhile, Rh particles in Li/RhY were embedded in the zeolite cages, which were narrowed by Li deposition on the wall. The size of the Rh particles was 0.8 nm in diameter. The Rh particles in Li/RhY were stable under reduction, CO adsorption, and CO2 hydrogenation conditions. We concluded Li additive changed the stability of Rh particles in the supercage by modifying surface hydroxyl group concentration. © 2000 OPA (Overseas Publishers Association) N.V. Published by license under the Gordon and Breach Science Publishers imprint.

We have investigated the structure of Pt(A)/MgO and PtMo6/MgO catalysts which were prepared from Pt(C5H7O2)(2) and [PtMo6O24](8-) followed by calcination, respectively, and their catalytic activities for the propane + O-2 reaction. The Pt(A)/MgO and PtMo6/MgO catalysts with atomically dispersed Pt ions were found to be as active as metallic Pt particles supported on MgO for propane combustion. A distorted spinel-like structure around Pt ion embedded at the MgO surface was proposed for the active Pt species by means of EXAFS. The atomically dispersed Pt structure was reduced with propane at 623 K to form Pt-6 clusters with Pt-O bonding to the MgO support. The Pt cluster chemically attached to the MgO surface was selective for the propane dehydrogenation. Restructuring of the Pt clusters to the atomically dispersed Pt structure was observed by oxidation with O-2 at 623 K. (C) 1999 Elsevier Science B.V. All rights reserved.

Ru/TiO2 catalysts were prepared by spray reaction (SFR) and conventional impregnation (IMP) methods. The catalytic activities of SPR fine particles were much higher than those of LMP catalysts for CO2 hydrogenation. A high temperature reduction greatly promoted the activity of SPR catalyst. A model of surface structure was proposed which exhibits the enhancement of decoration and the formation of more boundaries over spr-Ru/TiO2. The high activity of SPR catalyst is attributed to the occurrence of new active sites at the metal-support perimeters and not any SMSI phenomenon. EXAFS reveals that the Ru atom was interacting with TiO2 by oxygen atom so strongly on the SPR catalysts that a part of the Ru atoms, located near the internal interface between Ru particles and TiO2 support, existed as Run+ (n<4) cations even if SPR catalyst was subjected to a high temperature reduction. These Run+ cations are responsible for the inhibition of SMSI formation over SPR catalysts. (C) 1999 Elsevier Science B.V. All rights reserved.

We prepared relatively uniform supported Ru catalysts by ion-exchange and CVD methods, using an NaY zeolite and a mesoporous FSM-16 as substrates, and carried out CO2 hydrogenation. They showed high activity for CO2 hydrogenation. A Ru-ion-exchanged catalyst showed high activity for methanol production. Co addition promoted methanol formation.

Rhodium complex with a chiral phosphine ligand was intercalated into sodium hectorite by cation exchange method. The intercalation compound was characterized by FT-IR, XRD and TEM measurements. The basal spacing of the compound was estimated to be 2.29 rim from XRD measurement. This novel heterogenized catalyst exhibited a characteristic chiral as well as size recognition of the substrates in the hydrogenation of itaconates. (C) 1999 Elsevier Science B.V. All rights reserved.

CO2 hydrogenation (H-2/CO2=3, total pressure=3 MPa, 423 K) over Ph ion-exchanged Y-type zeolite catalysts (RhY) was studied. The RhY catalyst showed 10 times higher activity (as a turnover frequency) than a conventional impregnated SiO2-supported Ph catalyst (Rh/SiO2). Production of methanol was observed at 423 K over RhY. At first the Rh atoms were supported in a highly dispersed form in the zeolite cage. Then they began to aggregate under the reaction conditions, and moved outside the cage. The working state of Ph species was determined to be Rh metal particles (3.3 nm in diameter) located outside the cage; it was the same, regardless of the Ph loading (from 1 to 6 wt%). It was speculated that the high activity of the RhY catalyst was due to the zeolite cage, which played important roles to condense CO2 and to supply CO2 to the Rh sites outside the cage for the promotion of the reaction. Intense deactivation at 100 min was due to accumulation of produced water inside the zeolite cage, because it suppressed the CO2 reservoir inside the cage. (C) 1998 Elsevier Science B.V. All rights reserved.

Three series of Ru/Al2O3 catalysts were prepared by spray reaction (SPR), impregnation (IMP), and these two methods combined. The characteristics of multi-component SPR particles, as CO2 hydrogenation catalysts, were elucidated. The catalytic activity (TOF) of SPR fine particles was higher by one order of magnitude than that of IMP catalyst without any promoters. This is attributed to the formation of more active species at the perimeters between Ru metal and Al2O3 over SPR particles than over IMP catalysts. The addition of alkaline salts promoted the catalytic activity of Ru/Al2O3, irrespective of preparation methods employed. The promotion of alkali metals to Ru/Al2O3 catalysts is probably due to a synergetic effects including the modification of local electron density on Ru metal by the electron donation of alkali metals, the neutralization of residual chlorine ions by the formation of alkaline chloride, and the removal of depositional inactive carbon by alkaline carbonate catalysis. (C) 1998 Elsevier Science B.V. All rights reserved.

The crystalline carbon nanotubes having mesopores that are open at one end, with pore width of 4 +/- 0.8 nm, were characterized by XRD, XPS, and HRTEM. The N-2 adsorption isotherm of multiwall carbon nanotubes was measured at 77 K. A hump was observed near P/P-o = 0.4 in the adsorption isotherm, The adsorption isotherm was deconvoluted into those on the inner and external surfaces using the separately determined total, inner, and external surface areas. The adsorption isotherm on the inner surface was without adsorption hysteresis and had a sharp uptake at the P/P-o region corresponding to the mesopore width, which was ascribed to capillary condensation in the mesopores of carbon nanotubes.

Doped TiO2 photocatalysts were prepared by spray reaction method. The photocatalytic isomerization of cis-2-butene to 1-butene at 323 K has been employed to study a photocatalytic properties. The applicability of spray reaction method to the preparation of TiO2 and doped-TiO2 photocatalysts were proposed.

The behaviors of Rh particles and GeO2 submonolayers supported on SiO2 during oxidation and reduction have been investigated, revealing a structural change in the outermost support surface of supported metal catalysts, by means of XAFS, XRD, TEM and FTIR. Partial reduction of the GeO2 overlayers in Rh/GeO2/SiO2 occurred to form RhGe alloy particles by reduction with H-2 at 423-723 K, as proved by direct Rh-Ge bonding observed by EXAFS at both the Rh-and the Ge-K edges. The RhGe alloy particles were transformed to Rh oxides and GeO2 submonolayers by calcination at 673 K; conversely, these oxide phases were converted back to RhGe alloy particles by reduction at 423-723 K. These transformations on SiO2 took place reversibly during the oxidation-reduction treatments. This is a unique structural change at the Rh/GeO2 overlayer interface in contrast to the behaviors of Rh and Ge on bulk GeO, which were irreversible owing to subsidence of Rh into the GeO2 bulk.

An application of Ni/MgO catalyst which was prepared by using citric acid to the hydrogenation of carbon dioxide was investigated. The Ni/MgO catalysts with Ni content higher than 30 wt% were found to exhibit high catalytic activities for the hydrogenation of carbon dioxide due to the large Ni metal surface area. The usage of citric acid realizes the formation of NiO-MgO solid solution at a low temperature of 773 K. Aggregation of Ni metal particle is probably depressed by MgO highly dispersed in the Ni particle during the reduction of the NiO-MgO solid solution. A structural model of the Ni catalyst is proposed.

We measured Pt L(2,3)-edge X-ray absorption near edge structure (XANES) spectra for the Pt particles supported on SiO2, Al2O3 and MgO with and without adsorbed hydrogen. The new peaks appeared at 6-8 eV above the Pt L(2,3)-edges in difference spectra between those in vacuum and under hydrogen. The intensity of the new peak was found to be proportional to the amount of adsorbed hydrogen but independent of the kind of the supports, These results suggest that the XANES difference spectra provide a new method for in situ characterization of adsorbed hydrogen on supported Pt particles without interference of the support.

We measured Pt L(3), L(2) and L(1)-edges X-ray absorption near edge structure (XANES) spectra of Pt particles dispersed on metal oxide supports (SiO2, Al2O3 and MgO) with and without hydrogen adsorption. The difference spectra obtained by subtracting the spectra in vacuum from the ones with adsorbed hydrogen were independent of kind of the support and only dependent on the amount of adsorbed hydrogen. It was suggested that the change can not be only explained by the change of density of Pt 5d unoccupied state but by creation of a resonance state associated with the localized Pt-H interaction. We also found a linear relation between the change in the XANES spectra and the amount of adsorbed hydrogen, which provides a new characterization method for adsorbed hydrogen on supported Pt particles.

Interlayers of Na-hectorite (HT) and zirconium phosphate (ZrP) were modified with “chirality tuning guests” to enhance enantio-selective adsorption. The modified interlayers were characterized by means of spectroscopic techniques. The enantio-selective entrapments of alkylamines were studied, and their mechanisms will be discussed in terms of chiral pair formation. Regio-selective hydrogenation of geraniol was also found over multiply modified HT. © 1995, Elsevier B.V.