Yasukazu Saito

A new dual parameter scale for the strength of lewis acids and bases with the evaluation of their softness

Abstract A dual parameter scale has been proposed to represent the acidity of metal ions as Lewis acids. One parameter, X , is related to the electronegativity of the ion and is derived from the equation: (10 X) 1 2 = x i = x M 0 + (ΣI n ) sol1 2 , where x i and x M 0 are the electronegativities of the metal ion and the neutral metal atom, respectively, and I n is the n -th ionization potential ( M ( n −1) + → M n + ). Another parameter, Y , is calculated by Y = 10( I n / I n +1 )( r i /√ n ), where r i is the ionic radius of the metal ion and n is its formal charge. This parameter, Y , can be considered to express the tendency of a metal ion to form a dative pi-bond and consequently should correspond to its “softness”. The instability constant of a metal ion complex, K , can be described by these parameters as follows, p K = log K = αX + βY + γ , where α and β dual basicity parameters of the ligand corresponding to X and Y , respectively, and γ is a constant determined for each ligand. Some examples of the applications of these parameters are given.

Catalytic decalin dehydrogenation/naphthalene hydrogenation pair as a hydrogen source for fuel-cell vehicle

Abstract A catalytic decalin dehydrogenation/naphthalene hydrogenation pair has been proposed as a hydrogen source for fuel-cell vehicles in the present study. In order to evolve hydrogen from decalin efficiently under mild conditions, its catalytic dehydrogenation in a liquid-film type reactor was adopted with use of carbon-supported platinum-based fine particles under reactive distillation conditions. The catalyst layer was superheated in the liquid-film state, which gave much higher hydrogen evolution rates and conversions at 210°C than those in the suspended state. Requirements concerning high-evolution rates of hydrogen or high-power densities for practical fuel-cell vehicle operations would be fulfilled enough at around 280°C. As for the storage densities of hydrogen on both weight and volume bases (7.3 wt %, 64.8 kg-H 2 / m 3 ) , it is to be noted that their magnitudes are higher than the storage densities (6.5 wt %, 62.0 kg-H 2 / m 3 ) targeted by the Department of Energy, USA (DOE).

Liquid-film-type catalytic decalin dehydrogeno-aromatization for long-term storage and long-distance transportation of hydrogen

Abstract A new approach for mobile storage of hydrogen has been proposed with the use of a catalytic reaction pair of decalin dehydrogenation/naphthalene hydrogenation. With the complement of the industrialized naphthalene-hydrogenation catalysis, the other endothermic catalysis for decalin dehydrogenation was now performed at around 200°C with carbon-supported platinum-based catalysts. Under liquid-film conditions, hydrogen was evolved from decalin much more efficiently than the suspended ones due to the superheated states of dehydrogenation catalysts. It was confirmed that the catalytic conversions of decalin dehydrogeno-aromatization in the liquid-film states could surpass easily the equilibrium limit, because the conditions of suppressed reactant evaporation and reactive distillation were operative here. Exergy loss in the hydrogen storage system would be reduced tremendously by adopting this catalyst-assisted decalin/naphthalene pair as the medium of hydrogen carrier.

Contrast between nickel and platinum catalysts in hydrogenolysis of saturated hydrocarbons

Abstract In order to contrast the reaction mechanism of hydrogenolysis on nickel catalysts with that on platinum catalysts, the detailed analysis of initial reaction products in hydrogenolysis of five hexane isomers and methylcyclopentane was ensured by means of a pulse technique, using hydrogen as carrier gas for a gas Chromatographic microreactor. The hydrogenolytic products from reactants on nickel and platinum catalysts showed a very interesting contrast with each other at low conversion. Analogous to other reactions in hydrogen atmosphere, the reaction intermediates in hydrogenolysis are presumed to be normal alkyls -CH 2 (CH 2 2) n CH 3 on nickel catalysts, which are selectively hydrocracked owing to the successive α-scission to give methane as a main product. On the contrary, a carbonium ion mechanism has been proposed for platinum catalysts to interpret both the characteristic distribution of the initial hydrogenolytic products and the considerable skeletal isomerization during hydrogenolysis. Since heterolytic splitting of a carbon-hydrogen bond of saturated hydrocarbon gives a carbonium ion, the carbon-hydrogen heterolysis at the stage of adsorption on platinum catalysts may be due to the large stability of platinum-hydride coordination, which cannot be expected for the nickel-hydride case. The contrast between nickel and platinum catalysts in hydrogenolysis of saturated hydrocarbons is thus correlated with the nature of the carbon-hydrogen splitting, homolytic or heterolytic, at the stage of adsorption, which is understandable only in terms of the softness of the catalyst metals.

The classification of metal catalysts in hydrogenolysis of hexane isomers

Abstract The hydrogenolysis of hexane isomers has been studied on various supported metal catalysts (Fe, Co, Ni, Pd, and Pt) in the presence of hydrogen. The previous conclusion that there are two different mechanisms in the hydrogenolysis of saturated hydrocarbons on nickel and platinum catalysts has been found to hold generally on the above metal catalysts. From the product patterns in catalytic hydrogenolysis of hexane isomers, the catalysts could be classified into two groups, one containing Fe, Co, and Ni and the other containing Pd and Pt. This distinct difference cannot be explained by an intensive factor, but must be attributed to some more intrinsic property of these metals, because this contrast between the two groups is generally observed among several metal-catalyzed reactions. The effect of the support on the hydrogenolysis of hexane isomers was also investigated in the case of platinum and nickel catalysts. It was found that the differences observed between nickel and platinum were preserved on all supports used.

Rh2(OAc)4-PPh3 as a catalyst for the liquid-phase dehydrogenation of 2-propanol

The most active homogeneous catalyst hitherto known for the selective dehydrogenation of 2-propanol has been found to form from Rh2(OAc)4 by adding PPh3 in situ, although Rh2(OAc)4 itself possesses no catalytic activity. From the reaction solution a complex was isolated, 31P(1H) NMR of which showed that coordination of PPh3 occurs not only to the axial but also to the equatorial positions of the Rh-Rh axis. When this complex is used as a catalyst with PPh3 and acetic acid present, no induction period was observed, which appears for the catalyst generated in situ. Drastic changes in catalytic properties occurred by replacing Rh2(OAc)4 with Rh2(OCOCF3)4 or PPh3 with P(OPh)3, which indicate prospects of tailor-making the catalyst.

n-Alkene and dihydrogen formation from n-alkanes by photocatalysis using carbonyl(chloro)phosphine–rhodium complexes

n-Alkenes and dihydrogen were obtained from n-alkanes by photocatalysis using carbonyl(chloro)phosphine–rhodium complexes; the rate of alkane dehydrogenation was the same as that of propan-2-ol dehydrogenation under the same photocatalytic reaction conditions.

Lithium ion conductivity of A-site deficient perovskite solid solutions

Abstract Over twenty of A-site deficient perovskite solid solution with Li + ion conductivity (Li-ADPESSs) were prepared with the M and Li concentration fixed at M 0.56 Li 0.33 TiO 3 in the five series: (A) (La 1− X Nd X ) 0.56 Li 0.33 TiO 3 , (B) La 0.56 Li 0.33 M(IV) X Ti 1− X O 3 [M(IV)=Zr,Hf], (C) (Ca 1− X Sr X ) 0.56 Li 0.33 Ta 0.56 Ti 0.44 O 3 , (D) (Ca 1− X Sr X ) 0.56 Li 0.33 Fe 0.225 Ta 0.775 O 3 , E) Sr 0.56 Li 0.33 M(|||) 0.225 Ta 0.775 O 3 [M(|||)=Cr,Fe,Co,Ga,Y]. Except for the few, the quenched samples were the α-form with disordered arrangement of the A-site ions. The relation between bulk conductivity ( σ b ) and the cube root ( V 1/3 ) of the perovskite cell volume showed a maximum at V 1/3 ≈387 pm for the series A, B and at V 1/3 ≈395 pm for the series C–E, respectively. The perovskite framework containing less covalent, large cations calls for a larger optimal cell volume for fast conduction.

Improvements on thermal efficiency of chemical heat pump involving the reaction couple of 2-propanol dehydrogenation and acetone hydrogenation

Abstract Rapid catalytic dehydrogenation of 2-propanol by heating with low-quality thermal energy (ca 80 °C) and heat removal for fractional condensation of evolved gases at ambient temperature (ca 25 °C) make it possible to obtain high-quality thermal energy (ca 200 °C) from the hydrogenation heat of acetone. It has been found that the thermal efficiency of such a chemical heat pump can be greatly improved by adopting a Ru or more preferably Ru-Pt catalyst and conducting the reaction in a liquid-film state for the dehydrogenation (endothermic) process. The evolved gas was found to contain acetone exceeding the chemical reaction equilibrium in the gas phase, even when the reaction was performed under the stationary condition. Under such conditions, quite a high value was attained for both the fraction of heat used for the endothermic reaction (25.6%) and the exergy efficiency (58.6%). Advantages of the proposed catalytic system are discussed.

Catalytic dehydrogenation of methanol with ruthenium complexes

Abstract Dihydrogen was evolved at sufficiently high reaction rates from the methanol solution of ruthenium chloride under reflux conditions in the presence of an excess of sodium methoxide, with small amounts of sodium hydroxide. An activation energy of 123 kJ mol−1 was obtained for the methanol solution containing sodium methoxide (20 wt.%). At low sodium methoxide concentrations, however, removal of the Cl− ligand from the ruthenium species by adding silver tetrafluoroborate accelerated the reaction. Sodium formate was ascertained to be the reaction product in the solution. The correlation between the coordination structure of ruthenium and the catalytic activity is discussed.