Nobuyuki Ichikuni

Effect of electronic structures of Au clusters stabilized by poly(N-vinyl-2-pyrrolidone) on aerobic oxidation catalysis.

Au clusters smaller than 1.5 nm and stabilized by poly(N-vinyl-2-pyrrolidone) (PVP) showed higher activity for aerobic oxidation of alcohol than those of larger size or stabilized by poly(allylamine) (PAA). X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy of adsorbed CO, and X-ray absorption near edge structure measurements revealed that the catalytically active Au clusters are negatively charged by electron donation from PVP, and the catalytic activity is enhanced with increasing electron density on the Au core. Based on similar observations of Au cluster anions in the gas phase, we propose that electron transfer from the anionic Au cores of Au:PVP into the LUMO (pi*) of O(2) generates superoxo- or peroxo-like species, which plays a key role in the oxidation of alcohol. On the basis of these results, a simple principle is presented for the synthesis of Au oxidation catalysts stabilized by organic molecules.

A New Binding Motif of Sterically Demanding Thiolates on a Gold Cluster

A gold cluster, Au(41)(S-Eind)(12), was synthesized by ligating the bulky arenethiol 1,1,3,3,5,5,7,7-octaethyl-s-hydrindacene-4-thiol (Eind-SH) to preformed Au clusters. Extended X-ray absorption fine structure, X-ray photoelectron spectroscopy, and the fragmentation pattern in the mass spectrometry analysis indicated that formation of gold-thiolate oligomers at the interface was suppressed, in sharp contrast to conventional thiolate-protected Au clusters.

Microfluidic Synthesis and Catalytic Application of PVP-Stabilized, ∼1 nm Gold Clusters

Small PVP-stabilized gold clusters were successfully prepared by the homogeneous mixing of continuous flows of aqueous AuCl 4 (-) and BH 4 (-) in a micromixer. Spectroscopic characterization revealed that microfluidic synthesis could yield monodisperse Au:PVP clusters with an average diameter of approximately 1 nm, which is smaller than clusters produced by conventional batch methods. These approximately 1 nm Au:PVP clusters exhibited higher catalytic activity for the aerobic oxidation of p-hydroxybenzyl alcohol than did Au:PVP clusters prepared by batch methods.

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.

Selective Photocatalytic Oxidation of Alcohols to Aldehydes in Water by TiO2 Partially Coated with WO3

Semiconductor TiO(2) particles loaded with WO(3) (WO(3)/TiO(2)), synthesized by impregnation of tungstic acid followed by calcination, were used for photocatalytic oxidation of alcohols in water with molecular oxygen under irradiation at λ>350 nm. The WO(3)/TiO(2) catalysts promote selective oxidation of alcohols to aldehydes and show higher catalytic activity than pure TiO(2). In particular, a catalyst loading 7.6 wt % WO(3) led to higher aldehyde selectivity than previously reported photocatalytic systems. The high aldehyde selectivity arises because subsequent photocatalytic decomposition of the formed aldehyde is suppressed on the catalyst. The TiO(2) surface of the catalyst, which is active for oxidation, is partially coated by the WO(3) layer, which leads to a decrease in the amount of formed aldehyde adsorbed on the TiO(2) surface. This suppresses subsequent decomposition of the aldehyde on the TiO(2) surface and results in high aldehyde selectivity. The WO(3)/TiO(2) catalyst can selectively oxidize various aromatic alcohols and is reusable without loss of catalytic activity or selectivity.

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.

Ni/Mgo catalyst prepared using citric acid for hydrogenation of carbon dioxide

Abstract 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.

Selective synthesis of organogold magic clusters Au54(C≡CPh)26.

Organogold clusters Au(54)(C(2)Ph)(26) were selectively synthesized by reacting polymer-stabilized Au clusters (1.2 ± 0.2 nm) with excess phenylacetylene in chloroform.

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.