Susumu Tsuchiya

Rare earth metals as hydrogenation catalysts of unsaturated hydrocarbons

Abstract To elucidate the characteristics of rare earth metallic catalysts the hydrogenation of unsaturated hydrocarbons (ethene, propene, 1-butene, 1,3-butadiene, ethyne, propyne, and benzene) were carried out around ambient temperature using samarium and ytterbium particles formed by clustering metal atoms in frozen organic matrices by metal vapor techniques. In the hydrogenation reactions the rare earth metallic catalysts discriminated between the CC double bonds and triple bonds; alkenes, dialkenes, and aromatic compounds were readily hydrogenated, whereas alkynes were not hydrogenated at all. However, enhanced isomerization activity of propyne to propadiene was observed. The addition rates of hydrogen to alkenes were represented on coordinates of a first-order equation: v = kP H 2 . Preliminary kinetic studies suggest that the reaction is controlled by the hydrogen adsorption process. This identification is reinforced by the H 2 -D 2 isotope scrambling measurements. The hydrogenation of 1,3-butadiene by the rare earth catalysts was completely selective for alkene formation, and the yield of 2-butene was relatively high (>80%) with a high trans:cis ratio (2 ~ 20). The mode of hydrogen addition to the diene was examined using isotope techniques, indicating that 1-butene and 2-butene were formed by 1: 2- and 1:4-addition of hydrogen to 1,3-butadiene, respectively. In addition, it was found that the molecular identity of hydrogen was conserved during the hydrogenation of unsaturated hydrocarbons.

Hydrogen absorption in modified intermetallic compound systems

Abstract The modification of Mg 2 Ni by various organic compounds was investigated with a view to improving its hydrogen absorption properties. In particular Mg 2 Ni reversibly absorbed hydrogen under more moderate conditions when it had been modified with tetracyanoethylene or phthalonitrile. Studies of the treated materials using electron spin resonance and electronic spectra showed the formation of electron donor-acceptor (EDA) complexes owing to the high electron affinity of the organic species used. It is believed that the EDA complexes formed on the surface layer provide sites for hydrogen activation which is followed by the diffusion of excess hydrogen into the underlying intermetallic phase. This is consistent with the results of X-ray analysis and thermodynamic measurements.

Exceptionally active magnesium for hydrogen storage: Solvated magnesium clusters formed in low temperature matrices

Abstract It was found that the cocondensation of magnesium atoms with tetrahydrofuran vapour on a cooled surface (77 K) leads to the formation of magnesium aggregates which are exceptionally active for hydrogen absorption under mild conditions. The active magnesium clusters immediately began to absorb hydrogen without the conventional activation treatments even at about 473 K under atmospheric pressures. The present study is concerned with the evaluation of the magnesium clusters formed in low temperature matrices as a hydrogen storage medium. Further, attention is directed towards changes in the surface properties of magnesium caused by treating it with aromatic molecules in connection with the process of hydrogen absorption.

Effects of lanthanide metals in Eu–Ni and Yb–Ni bimetallic catalysts

Lanthanide metals (Eu and Yb) dissolved in liquid ammonia and reacted readily with reduced Ni powders to form Eu–Ni and Yb–Ni bimetallic catalysts with different lanthanide contents. The catalysts were characterized by the hydrogenolysis of ethane and cyclohexane, the hydrogenation of ethene, hydrogen chemisorption and temperature-programmed desorption (TPD) measurements. The rate of hydrogenolysis decreased markedly when Yb and Eu were added to the Ni surface, whereas the hydrogenation activity showed a tendency to increase, especially in the Eu–Ni system. The lanthanide itself showed a low activity for the hydrogenolysis and hydrogenation reactions under the reaction conditions. An analysis of the decrease in the rate of hydrogenolysis with lanthanide addition suggested a decrease in concentration of surface nickel available for structure-sensitive reactions caused by lanthanide coverage. For the hydrogenation of ethene the surface was gradually covered with the lanthanide metals and simultaneously certain interactions occurred to produce active centres; the presence of lanthanide metals on Ni strongly influenced the state of adsorption of hydrogen in the subsequent activation processes, resulting in enhanced capacity of this surface to dissociate hydrogen. For the hydrogenation of ethene and adsorption characteristics, lanthanide and transition metals were more efficient when they were used together.

Application of organic compounds to metal-hydrogen systems as a technique for improving sorption properties: A new class of hydrogen absorbers

Abstract A technique for using organic materials to improve the sorption properties of magnesium-based hydrogen storage media is presented. Two approaches are possible. First, Mg 2 Ni and SmMg 3 reversibly absorb hydrogen under more moderate conditions when they have been modified with various organic compounds (anthracene, phenanthrene, chrysene, perylene, naphthacene, phthalonitrile, tetracyanoethylene or chloranil). The hydriding behaviour of modified Mg 2 Ni and SmMg 3 is associated with the formation of electron donor-acceptor (EDA) complexes by charge transfer between the alloy particles and the organic modifiers. The process of hydrogen uptake is explained by “hydrogen spill-over”, in which hydrogen species in an atomiclike form which have been activated at the EDA sites rapidly migrate to react with the adjoining alloy particles. Second, small solvated magnesium particles formed by clustering in low temperature organic matrices (tetrahydrofuran, benzene, pentane or ethyl ether) are exceptionally active and immediately begin to absorb hydrogen without requiring “activation”. The hydrogen sorption characteristics of these magnesium-organic compound systems are elucidated. The exceptional activity of these systems can be partially interpreted in terms of their structural geometry compared with that of pure magnesium. The organic matrix in which the magnesium atoms are dispersed and in which crystal growth proceeds has pronounced effects on the shape, size and catalytic properties of the particles formed.

Ethylene hydrogenation over lanthanide-doped Cu and Ag catalyst systems (EuCu, YbCu, EuAg and YbAg)

Abstract Metal powders (Cu and Ag) react readily with Eu and Yb which dissolve in liquid ammonia, resulting in the formation of active lanthanide-doped catalysts (EuCu, YbCu, EuAg and YbAg). The catalytic properties of the samples with varied levels of lanthanide doping have been evaluated in the hydrogenation of ethylene. For EuCu and YbCu the hydrogenation activity increased rapidly with the lanthanide addition and then gradually; increases of over three or four orders of magnitude compared with the constituent metals alone were observed. The activity of Eu-containing systems was, in most cases, higher than that of the Yb-containing systems. The catalytic behaviour was markedly dependent on the evacuation temperatures of the catalysts before reaction. This is due to the reconstruction of surface morphology with an increase in the pretreatment temperature, which brings about the interaction between the lanthanide and transition metals to form active sites synergistically. This phenomenon is most probably associated with appearance of high catalytic activity for the present systems. The nature of the active sites formed and the effect of lanthanide addition are discussed.

Lanthanide (Eu or Yb)-promoted Ni, Cu and Ag-catalyzed transfer hydrogenation with NH3 as a hydrogen donor

Abstract Novel lanthanide (Ln)-promoted Ni, Cu and Ag catalysts prepared by the reaction of Ni/SiO2, Cu/SiO2 and Ag/ZrO2 with the dissolved Eu or Yb metals in liquid ammonia have been studied for the catalytic transfer hydrogenation of ethene, buta-1,3-diene and propyne. The transfer hydrogenation with the aid of ammonia as a hydrogen donor was greatly enhanced by the Ln-promoted catalysts. The catalytic activity for the transfer hydrogenation increased with increasing lanthanide content in the bimetallic catalysts, which evidently reflected synergetic effects between the lanthanide and transition metals. The transfer hydrogenation of ethene with ammonia over Eu–Ni/SiO2 proceeded to form ethane and nitrogen, maintaining the following stoichiometric relationships: 3C2H4+2NH3→3C2H6+N2 The catalytic hydrogen transfer from ammonia to buta-1,3-diene or propyne similarly followed the stoichiometric relationships. The Ln-promoted catalysts showed substrate selectivity for the transfer hydrogenation using ammonia as the hydrogen source; Ln–Ni/SiO2 was reactive for ethene and buta-1,3-diene, but not for propyne. Ln–Cu/SiO2 was active for propyne and buta-1,3-diene. Ln–Ag/SiO2 was relatively active for buta-1,3-diene. The major factors governing the catalytic transfer hydrogenation seem to be involved in the participation of the acceptor and donor molecules in the hydrogen transfer step rather than the ease of dehydrogenation of ammonia and the processes of hydrogen addition to the acceptor. The catalytic hydrogen transfer from ammonia to acceptor molecules occurs concertedly.

Selective lanthanide-catalysed reactions. Catalytic properties of Sm and Yb metal vapour deposition products

The characteristics of lanthanide catalysts obtained when Sm and Yb were vaporized into a frozen organic (tetrahydrofuran, benzene and methyl-cyclohexane) matrix (77 K) were investigated. These low-valent, highly dispersed lanthanide particles (indicated as Sm/THF, Sm/benzene, Yb/THF, Yb/benzene etc.) were catalytically active and selective for hydrogenation and isomerization. Samarium usually showed a greater activity than ytterbium. Olefin [ethene, propene, but-1-ene and (z)-but-2-ene] hydrogenation obeyed the rate law v=kPH, suggesting that the reaction is controlled by catalytic activation of hydrogen. The molecular isotopic identity of hydrogen was conserved during the hydrogenation. Yb/THF and Yb/benzene were active for partial hydrogenation of benzene to cyclohexene. For the hydrogenation of olefins and acetylenes the substrate specificity was high; thus C—C double bonds were more readily reduced than triple bonds. The samarium and ytterbium catalysts discriminate between terminal and internal C—C triple bonds, only internal CC bonds (but-2-yne and pent-2-yne) being reduced very selectively in contrast to acetylene, methylacetylene and but-1-yne. Solid base character of the lanthanide provides a cause for these differences in catalytic properties.

Hydrogen storage composites obtained by mechanical grinding of magnesium with graphite carbon

Novel hydrogen storage Mg/G composites prepared by mechanical grinding of magnesium (Mg) and graphite carbon (G) with benzene have been found to incorporate new hydrogen-storing sites, other than those due to the magnesium component, and can take up hydrogen reversibly.

Magnesium-based hydrogen-storage materials: Solvated Mg-Ni by metal vapour deposition

Abstract The solvated alloy Mg-Ni (88–94 wt.% magnesium; 0.6–6 wt.% nickel), prepared by dispersing metal atoms into a frozen organic matrix by metal vapour deposition, exhibited exceptionally active hydrogenation capability under mild conditions. Organic species retained in the metal clustering process stabilize the small particles by acting as modifiers and prevent them from sintering. In solvated Mg-Ni, small nickel particles in the 1–4 nm diameter range were highly dispersed on magnesium particles with large surface areas (94–108 m 2 g − 1 ). The hydride formation which was accelerated enormously by dispersed nickel is probably controlled initially by surface reactions.