Osamu Takayasu

Progress of enantio-differentiating hydrogenation of prochiral ketones over asymmetrically modified nickel catalysts and a newly proposed enantio-differentiation model

This article reviews the enantio-differentiating hydrogenation of various prochiral ketones over asymmetrically modified Ni catalysts. Development from the discovery to the state of the art of the modified Ni catalyst is surveyed. Understanding and interpretation of this catalyst is discussed and new enantio-differentiation models are proposed.

Application of an in situ modification of nickel catalysts to the enantio-differentiating hydrogenation of methyl acetoacetate

Abstract In situ modification (( R , R )-tartaric acid and NaBr were directly added to the reaction media) of fine Ni powder (FNiP) and reduced Ni catalysts was applied to the enantio-differentiating hydrogenation of methyl acetoacetate (MAA). The high optical yield of 89% was attained by the reduced Ni catalyst. This is the highest value reported so far for the hydrogenation of methyl acetoacetate using the in situ modification. The addition of a small amount of NaBr to the reaction media increased both the optical yield and hydrogenation rate, while the hydrogenation rate decreased with the addition of NaBr to the modification solution for the conventional modification method. NaBr added to the reaction media for the in situ modification would have both of the following roles: (i) Na + increased the optical yield and the hydrogenation rate; and (ii) Br − increased the optical yield and decreased the hydrogenation rate.

Catalytic inactivities of Ni alloys expressed by surface and bulk compositions

The surface compositions of three kinds of powdered alloys with different structures, CuNi (fcc-fcc), FeNi (bcc-fcc), and CoNi (hcp-fcc), were determined by the penetration of β-rays of 63Ni mixed previously in the alloy, then the effect of the respective alloy structure both of the surface and of the bulk on the catalytic hydrogenation of ethylene was studied. The surfaces of these alloys were found to be Ni-poor for the wide range of alloy composition. The catalytic activity expressed by each surface composition was difficult to explain by the physicochemical properties of the surface. The activity expressed by the bulk composition of CuNi of fcc structure was high in the region of unfilled d-band, and so were that of FeNi and that of CoNi in the region of fcc structure. The activity of FeNi for the dimerization of 14C-ethylene was studied, of whose activity the similar tendency was observed as found in the hydrogenation reaction. These could be interpreted as the results of the positive contribution of the dissolved hydrogen in bulk to the catalytic reactions.

High durability of asymmetrically modified nickel catalysts prepared by in situ modification

Abstract The in situ modification of a reduced Ni catalyst at the first run showed a high durability for the repeated use with high optical yields in the enantio-differentiating hydrogenation of methyl acetoacetate. Reduced Ni from Ni oxide and fine Ni powder were the best materials in comparison with Raney Ni. For attaining high optical yields and high durability, in situ modification and a Ni surface suitable for the enantio-differentiating hydrogenation are necessary. One of the reasons for the low durability of the conventional pre -modified Ni with repeated use would be the desorption of tartaric acid from the catalyst surface during the hydrogenation reaction.

Enantio-differentiating hydrogenation of methyl acetoacetate over tartaric acid-NaBr-modified supported nickel catalyst prepared from nickel acetylacetonate

Abstract Supported nickel catalysts were prepared from nickel acetylacetonate, and then modified in a solution containing tartaric acid and sodium bromide. The enantio-differentiating hydrogenation of methyl acetoacetate was carried out over this catalyst. The effects of the preparation variables of the supported nickel catalysts on the optical yield and the effects of the conditions for the nickel surface modification on the optical yield were examined. The catalysts were also characterized by XRD and TEM. The maximal optical yield of 87% was attained when crystallized α-alumina (sumico rundum) was used as a support.

Enantio-differentiating hydrogenation of methyl acetoacetate over fine nickel powder with in situ modification

Enantio-differentiating hydrogenation of methyl acetoacetate (MAA) was carried out using fine nickel powder (FNiP) by adding tartaric acid (TA) and sodium salts to the reaction media (in situ modification) instead of using a conventionally modified nickel catalyst. This catalyst prepared by the in situ modification gave an optical yield up to 79%.

Spillover effect for the reducing reaction of CO2 with CH4 over SiO2-supported transition metal catalysts physically mixed with MgO

Abstract It was demonstrated that a Ni catalyst supported on MgO was a better performing catalyst than that of Ni on SiO2 for the partial oxidation reaction of CH4 with CO2 to give syngas, but unfortunately the lifetime of Ni/MgO was shorter than Ni/SiO2 because of carbonaceous deposits. These weak points were improved by physically mixing these catalysts with MgO or α-Al2O3. These findings were explained by the spillover of hydrogen.

The reduction mechanism of powdered copper-nickel oxides

Abstract The mechanism of the formation of copper-nickel alloys from copper and nickel nitrates by calcination and by reduction with hydrogen was investigated by means of X-ray diffraction and measurement of the rate of the reduction. X-ray diffraction showed that the unreduced copper-nickel oxides were composed of cupric oxide and miscible oxide of nickel and copper. Cuprous oxide and free nickel did not appear in the process of reduction. The completely reduced copper-nickel was composed of nickel-rich alloy and extremely copper-rich alloy. The rate of reduction of copper-nickel oxide was practically the same as that of cupric oxide. From these results and the change in the BET areas, it was concluded that the alloys are formed by the interdiffusion of nickel into a copper phase which forms earlier than nickel.

Deactivation of Ni-Catalysts and Its Prevention by Mechanically Mixing an Oxide for the Formation Reaction of CO+H2 from CO2+CH4

The CO 2 reforming reaction of CH 4 to give syngas was examined in two types of catalysts. One type is the Ni-supported catalysts on an unreducible oxide such as SiO 2 , MgO, and α-Al 2 O 3 and the other is the mechanically mixed catalysts of the Ni-supported catalyst with another unreducible oxide. Endurance tests showed three main types of deactivation curves for these catalysts. XRD analysis after the endurance tests and thermogravimetric analysis showed the reason for the occurrence of these three types. One is concerning Ni/SiO 2 , etc. whose abrupt deactivation occurred during the first 100 h and subsequent slow deactivation by the increase of Ni particle size. The second one is concerning Ni/α-Al 2 O 3 , etc. whose initial activity was very high but at a few hundred hours an abrupt deactivation started by the formation of NiAl 2 O 4 . The third one is concerning Ni/MgO, etc. whose deactivation was very slow partly due to the formation of carbonaceous deposits. This problem on Ni/MgO was overcome by mechanically mixing it with SiO 2 or by using a CO 2 excess feed.

Study of the parameters controlling the enantio-differentiating ability of asymmetrically modified solid catalysts for the hydrogenation of γ-ketoesters

The enantio-differentiating hydrogenation of γ-ketoesters was carried out over asymmetrically modified solid catalysts. The parameters affecting the enantiomer excess (ee) were investigated and the results were compared with those of the hydrogenation of methyl acetoacetate and 2-octanone reported in the literature. The highest value of enantiomer excess of 51% was attained for the hydrogenation of methyl 4-oxopentanoate over a tartaric acid (TA)-NaBr-modified reduced nickel catalyst prepared from nickel oxide. The amount of NaBr in the modification solution needed to be optimized according to the manufacturers of the nickel oxides. The addition of an appropriate amount of carboxylic acid to the reaction media increased the enantiomer excess of the hydrogenated products.