Noritetsu Yoshida

Solution of hydrogen in thin palladium films

Solubility enhancements have been observed for hydrogen in thin Pd films (250–820 A) in the αphase. Thermodynamic data for the films are determined from isotherms at temperatures between 25 and –40 °C and are compared with those for bulk Pd. From the values of WH—H(interaction energy of hydrogen in the film) and the solvus behaviour, it is suggested that the hydride phase in the films is destabilized relative to the dilute phase as the film thickness decreases. The dependence of the solubility on annealing has been examined for a thin film. The results indicate that the special characteristics of thin films disappear after annealing at ca. 400 °C.

On the hyperfine deuterium distribution of the catalytic reaction of propene with deuterium on copper powders

Abstract The hydrogenation mechanism of propene on a copper catalyst was investigated at room temperature, using deuterium as the reactant instead of protium. Thereby, not only distributions of the produced deuteropropenes and deuteropropanes were determined by mass spectrometry, but also distributions of the deuterated positions in both monodeuteropropenes and monodeuteropropanes were determined, respectively, by microwave spectrometry and NMR spectrometry. From these two distributions, an extended associative mechanism could be confirmed by assuming half-hydrogenated intermediates of the types CH 3 -CH 2 - C ∗ H 2 and CH 3 - C ∗ H-CH 3 , even though the deuterium-exchange reaction occurs much more frequently via the former species. Double-bond migration was confirmed during the reaction, as has already been proposed on nickel catalyst. Some caution is pointed out on the use of the random-distribution law in discussing the reaction mechanism on the basis of deuterium distribution.

Application of microwave spectroscopy to the isotopic analysis of the reaction products of methylacetylene with deuterium on nickel catalysts

Abstract The reaction of methylacetylene with deuterium was investigated in a static system over nickel powders at 25 °C, and the products were analyzed by the mass spectroscopic and microwave spectroscopic methods. The propylene yield in the products was ca. 0.8, similar to the result presented in the literature. In sharp contrast with the reaction of propylene with deuterium, the methyl positions of propylene could not be deuterated, suggesting that the double-bond migration does not occur during the reaction. Of all the propylene- d 2 , cis -dideuteropropylene consisted of more than half the product at the 70% conversion. Protium concentration on the surface was estimated to be very low during the reaction. This is in contrast to the situation in the reaction of olefins with deuterium.

MICROWAVE STUDY OF THE ADSORBED SPECIES IN THE DEUTERIUM-EXCHANGE REACTIONS OF PROPYLENE WITH REFERENCE TO ITS CATALYTIC HYDROGENATION.

Synopsis Deuterium-exchanged positions of the monodeuteropropylene produced in the exchange reactions relating to propylene were investigated on Gu and Rh by means of the microwave spectroscopy, similarly as done on Ni, Pd and Pt in the previous reports. Information thus obtained gave us several important knowledge; e.g., the adsorbed species of propylene are drastically different according to metals, and double-bond migration occurs during the adsorption and desorption processes of propylene.

Solution of hydrogen in thin films of a palladium–silver alloy

The absorption of hydrogen in evaporated Pd–Ag (5–7 atom % Ag) films with thicknesses of 360, 1150 and 2160 A has been studied volumetrically from –40 °C to room temperature. Thermodynamic parameters in the range of the α-phase have been determined for the films and are compared with those for bulk alloys. It is found that the hydrogen solubilities in the films are larger than in the bulk alloys, and these tend to increase with decreasing film thickness. The absolute values of WHH(the interaction energy of dissolved hydrogen) for the films are much smaller than those for the bulk alloys, and these values are found to increase with an increase in the film thickness. It is suggested that the solubility enhancement in the α-phase and the weakening of H–H interactions are mainly caused by stresses which are created during the deposition of the films.

Calculation of Elementary Reaction Rates in the Catalytic Hydrogenation of Propylene on Copper

By applying the theory due to Yasuda and Hibota in the preceding paper to the catalytic hydrogénation of propylene on copper powders at room temperature, reaction rates at some elementary steps are calculated throughout the reaction from deuterium-distributions in all the reactants and products which were produced in the reaction between propylene and deuterium (2:1). A ratediagram describing the variation in the reaction rates shows that reaction mechanisms at some elementary steps should not be considered independently and that the role of physically adsorbed hydrocarbons is not to be disregarded for a correct understanding of the whole reaction-mechanism.

Isotopic Composition of Chemisorbed Hydrogen during the Reaction of Propylene with Deuterium on Copper

還元粉糊触媒輔いて,25℃でプロピレンの重水素化反応を行なわせ,反応の進行にともなって変化する気相水素の同位体組成(H2,HD,D2)を質量分析計で測定した。その結果,反応初期においては,H3の生成速度がHDの生成速度よりも大きかった。これは100%D2との反応にもかかわらず,触媒表面に解離吸着している水素原子は軽水素原子が大部分で,重水素原子が少ないことを示唆している。そこで著者らはこの測定値を用い,水素の解離吸着過程と吸着水素原子の脱離再結合過程における同位体効果が無視し得るものと仮定して,吸着水素原子中の重水素原子の割合(表面重水素濃度)を計算したところ,反応初期での表面重水素濃度は15%であった。この値はすでに轍告したこの系におけるプロピレンとプロパンの重水素分布の結果とも合致する。それゆえ, この結果はオレフィン水素化反応の機作として一般に受け入れられている会合機作によって説明することができる。