Shogo Shimazu

Hydrogenation of CO2 over sprayed Ru/TiO2 fine particles and strong metal–support interaction

Ru/TiO2 catalysts were prepared by spray reaction (SPR) and conventional impregnation (IMP) methods. The catalytic activities of SPR fine particles were much higher than those of IMP 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.

Catalytic properties of sprayed Ru/Al2O3 and promoter effects of alkali metals in CO2 hydrogenation

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.

Highly efficient and selective hydrogenation of unsaturated carbonyl compounds using Ni–Sn alloy catalysts

Inexpensive Ni–Sn-based alloy catalysts, both bulk and supported, exhibited high selectivity in the hydrogenation of a wide range of unsaturated carbonyl compounds and produced unsaturated alcohols almost exclusively. For the bulk Ni–Sn alloy catalysts, a relatively high reaction temperature of 453 K was required to achieve an efficient hydrogenation of CO rather than CC. The catalyst that consisted of the Ni–Sn alloy dispersed on TiO2 allowed a remarkable reduction of the reaction temperature to 383 K. Both the Ni3Sn2 and Ni3Sn alloy phases were found to be responsible for the enhancement of the chemoselectivity. The Ni–Sn alloy catalysts were reusable without any significant loss of selectivity.

Asymmetric hydrogenation of α,β-unsaturated carboxylic acid esters by rhodium(I)-phosphine complexes supported on smectites

Abstract Hectorite(HT)-supported Rh complex catalysts were prepared by the interaction of [Rh(P ∗ −P ∗ )(COD)] + (P ∗ −P ∗ = ( S )-BINAP and ( S )-( R )-BPPFA, COD - cyclooctadiene) into sodium hectorites (NaHT) in acetonitrile/H 2 O. The basal spacing of each modified clay was 2.94 nm (BINAP) and 2.72 nm (BPPFA), respectively. Asymmetric hydrogenation of α,β-unsaturated carboxylic acid esters containing ester groups of various chain lengths was studied on these modified hectorites. The dependence of selectivity on employed solvents and bulkiness of the ester groups suggested that the interaction between substrates and the active sites increased in the interlayer space, thus enhancing the asymmetric selectivity.

Creation of highly stable monomeric Pd(II) species in an anion-exchangeable hydroxy double salt interlayer: Application to aerobic alcohol oxidation under an air atmosphere

An active Pd(II) catalyst supported on the Ni–Zn mixed basic salt (NiZn), which is classified by the anion-exchangeable layered hydroxy double salts, was synthesized by simple intercalation of the anionic Pd(II) hydroxyl complex. The divalent Pd species in the interlayer of NiZn maintained their original monomeric structure during the aerobic alcohol oxidation, due to the strong electrostatic interaction between the NiZn host and anionic Pd(II) species. This catalyst could be reused without any loss of the catalytic activity and selectivity in the aerobic alcohol oxidation.

Asymmetric hydrogenation of itaconates by hectorite-intercalated Rh-DIOP complex

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 nm from XRD measurement. This novel heterogenized catalyst exhibited a characteristic chiral as well as size recognition of the substrates in the hydrogenation of itaconates.

Preparation of clay-supported Sn catalysts and application to Baeyer–Villiger oxidation

Clay-intercalated Sn catalysts were prepared by a conventional cation-exchange method and used for the Baeyer–Villiger oxidation of various ketones with hydrogen peroxide as an oxidant. The intercalation of monomeric Sn species into the clay interlayer was monitored by solid-state 7Li MAS NMR. Solid-state 119Sn MAS NMR and Sn K-edge XAFS analysis revealed that an isolated Sn species, such as [SnIV(OH)x(H2O)5−x](4−x)+ (x = 0–3), was formed in the clay interlayers. Our clay-intercalated Sn catalysts showed extremely high performance in Bayer–Villiger oxidation and were also reusable without any significant loss of activity or selectivity.

Promoting effect of NiAl2O4 for supported Ni particles on sprayed Ni/Al2O3 catalysts

Ni/Al2O3 catalysts were prepared by the spray reaction method. The NiO particles supported on NiAl2O4 were stabilized against the aggregation and converted into smaller Ni particles by H2 reduction. The Ni particles stabilized on NiAl2O4 marked anomalous high activity for CO hydrogenation, due to the stronger interaction between Ni and NiAl2O4.

Regioselective hydrogenation of dienes catalyzed by palladium–aminosilane complexes grafted on MCM-41

A palladium(II)-aminosilane complex supported on MCM-41 (Pd-AEAPSi/MCM (1)) was prepared by the complexation of palladium(II) acetate to 3-(2-aminoethyl)aminopropyl (AEAPSi) groups grafted on MCM-41. FT-IR and 13 C CP MAS NMR studies indicated that AEAPSi chelated to palladium(II) to form the Pd(II)-AEAPSi complex. Regioselective hydrogenation of dienes was carried out by the obtained 1 as a catalyst. Pd-AEAPSi/MCM exhibited remarkably high reaction rates for the dienes with a hydroxyl group such as geraniol and linalool, while for limonene without OH group the reaction rate was notably low. The MCM-supported catalyst also showed noticeably high regioselectivity in the hydrogenation of dienes with OH group. These results indicate that the hydrophilic interaction between the MCM-41 surface and the substrates plays an important role in the rate-determining step.

New application of spray reaction technique to the preparation of supported gold catalysts for environmental catalysis

Abstract Taking the advantage of the characteristic preparation method of nanocomposites particles, spray reaction was applied for the preparation of supported gold catalysts, i.e., Au/TiO2 and Au/Al2O3. The structure and the physical properties were characterized by means of powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), EXAFS and BET measurements. The exposed surface sites of metal were estimated by CO and/or NO adsorption. The marked catalytic activities for CO oxidation and NO–CO reaction were discussed in terms of the enhancement of synergistic effects due to the characteristic nanostructures.