Yuriko Nitta

Selective hydrogenation of αβ-unsaturated aldehydes on cobaltsilica catalysts obtained from cobalt chrysotile

Abstract Selective hydrogenation of cinnamaldehyde and crotonaldehyde has been studied under mild conditions with uniformly-dispersed cobalt-silica catalysts prepared by the reduction of cobalt chrysotile, Co3(OH)4Si2O5, and those prepared from silica-supported basic cobalt carbonate precipitated under different conditions. The selectivity for unsaturated alcohols was found to increase with increasing size of cobalt crystallites in the catalyst. The structure sensitivity of this reaction has been explained in terms of the strength of adsorption of the starting and the intermediate compounds on different surfaces of cobalt metal, on the basis of the results for competitive hydrogenation of saturated aldehyde and unsaturated alcohol. Satisfactorily high selectivities to unsaturated alcohols were obtained with a catalyst having a relatively large size of cobalt crystallite and with an appropriate choice of reaction conditions.

Surface state and catalytic activity and selectivity of nickel catalysts in hydrogenation reactions: III. Electronic and catalytic properties of nickel catalysts

Abstract Various nickel catalysts (nickel-boride, nickel-phosphide, Raney-nickel, Urushibara-nickel, and decomposed-nickel) were investigated to examine the relationships between catalytic and electronic properties of nickel catalysts modified by component elements (boron, phosphorus, aluminum, and zinc) in the catalysts. Based on the X-ray photoelectron spectroscopic results, a parameter Δ q was tentatively proposed to characterize the electronic properties of the catalysts. The specific activity (activity per surface area of nickel metal) for hydrogenation reaction, the adsorption equilibrium constant of acetophenone, the resistivity against poisoning, and the characteristic selectivities in hydrogenation of 1,2-butylene oxide were found to be summarized in terms of the parameter Δ q . It is suggested that Δ q is a useful parameter to reflect the electronic properties of the nickel catalysts.

Copper-zirconia catalysts for methanol synthesis from carbon dioxide : effect of ZnO addition to Cu-ZrO2 catalysts

Coprecipitated Cu-ZrO2 catalysts were found to show higher selectivity to methanol in CO2 hydrogenation than conventional Cu-ZnO catalysts. Addition of ZnO to Cu-ZrO2 catalysts of Cu/ZrO2 = 1 (weight ratio) greatly enhanced the activity at lower temperatures, while keeping the high methanol selectivity of Cu-ZrO2 catalysts. A remarkable increase in the Cu dispersion with increased amount of added ZnO explains the increased activity at lower temperatures, while the reforming of methanol to CO is accelerated by ZnO at higher temperatures, leading to a lowered yield of methanol. It is suggested that ZrO2 rather than ZnO in the ternary systems plays a more effective role for the selective formation of methanol.

Effects of preparation variables of supported-cobalt catalysts on the selective hydrogenation of α,β-unsaturated aldehydes

The effects of starting salts, supports, added amount of Na{sub 2}CO{sub 3}, and other precipitation variables on catalytic properties of supported cobalt catalysts were studied for the hydrogenation of cinnamaldehyde and crotonaldehyde by using TGA, XRD, and XPS. The catalysts prepared from cobalt chloride always exhibited high selectivities to unsaturated alcohols irrespective of the support employed. The amount of surface chlorine remaining after H{sub 2}-reduction of the Co/SiO{sub 2} precursors prepared from cobalt chloride decreased with increasing amount of Na{sub 2}CO{sub 3} added as the precipitant, and both activity and selectivity reached maxima at around Cl/Co = 0.2 in the catalyst surface. The enhanced selectivity of the catalyst prepared from cobalt chloride was explained by the effects of residual chlorine both in the H{sub 2}-reduction stage and in the reaction stage; the former leads to a favorable crystallite size distribution (CDS) of cobalt and the latter depresses the hydrogenation of C{double bond}C double bond. The difference in activities and selectivities of various supported catalysts prepared from cobalt nitrate was discussed based on the difference in the strength of metal-support interaction which leads to different CDSs of cobalt in theses catalysts.

Effect of preparation variables on enantioselectivity of supported nickel catalysts modified with tartaric acid

Abstract Enantioselective hydrogenation of methyl acetoacetate to methyl 3-hydroxybutyrate on various supported nickel catalysts modified with ( R,R )-tartaric acid was studied under mild reaction conditions in order to examine the effects of preparation variables on the enantioselectivity and activity of resulting catalysts. The selectivity of the supported nickel catalysts was strongly dependent on the precipitation conditions. The effect of reduction conditions on the selectivity depended on the kind of support. Even Ni-alumina catalysts, when reduced under relatively mild conditions, had high enantioselectivity although their hydrogenation activity was low. Ni-silica catalysts, precipitated under optimum conditions and reduced at 400–500 °C for 1–3 h, were much more active than the other catalysts with similar, high enantioselectivity. Various extents of the selectivity of supported nickel catalysts were explained in terms of the effect of preparation conditions on the crystallite size distributions of nickel.

Preparation chemistry of precipitated NiSiO2 catalysts for enantioselective hydrogenation

Abstract Effects of preparation conditions on chemical composition and reducibility of precipitated precursors of NiSiO 2 catalysts were studied using thermal gravimetric analysis. The proportion of NiCO 3 in the precursor decreased as the preparation conditions became severe and the reducibility of the precursor decreased with a decrease in the NiCO 3 content, suggesting stronger metal-support interaction of SiO 2 with Ni(OH) 2 than with NiCO 3 . The X-ray diffraction measurements showed that the mean crystallite size of nickel in H 2 -reduced catalysts increased with increasing NiCO 3 content in the precursor. The activity and selectivity of the modified catalysts in enantioselective hydrogenation of methyl acetoacetate depended on the proportion of NiCO 3 in the precursor and were explained in terms of crystallite size distribution of nickel in the catalysts.

Effect of starting salt on catalytic behaviour of Cu-ZrO2 catalysts in methanol synthesis from carbon dioxide

Starting salts used in the co-precipitation of Cu-ZrO2 precursors had marked influence on both activity and selectivity of resulting catalysts for methanol synthesis: chlorides increased the selectivity, suggesting the structure sensitivity of methanol formation reaction, while sulfates much enhanced the activity by affecting the dispersion of Zr species. A simultaneous use of copper chloride and zirconium sulfate greatly improved the activity and selectivity of the catalyst for methanol formation.

Effects of additives on morphological and catalytic properties of NiSiO2 catalysts for enantioselective hydrogenation

Abstract Effects of additives such as Pd and Cl in the preparation of precipitated NiSiO 2 catalysts have been studied by means of X-ray diffraction and thermal gravimetric analysis using various precursors with different compositions. Pd addition stimulates the reduction of NiCO 3 species in the precursors but scarcely improves the enantioselectivity of the H 2 -reduced catalysts. Cl addition causes an increase in the mean crystallite size of Ni and disappearance of small crystallites in the reduced catalysts probably by promoting the reduction of Ni(OH) 2 species having strong interaction with support. This explains the increased enantioselectivity and durability of the Cl-promoted catalysts. Mechanism of the crystallite size increase caused by the Cl addition has been discussed.

Kinetic studies of enantioselective hydrogenation of methyl acetoacetate on modified NiSiO2 catalyst

Abstract Enantioselective hydrogenation of methyl acetoacetate (MAA) to methyl 3-hydroxybutyrate (MHB) on tartaric acid-modified NiSiO 2 catalyst was studied under H 2 pressures from 1 to 130 kg/ cm 2 in order to examine the effects of reaction conditions on optical purity of the product. Three kinds of autoclaves equipped with different stirring systems were used. Under the condition where the rate is controlled by surface reaction, the optical yield of MHB decreased with increasing H 2 pressure, and, at constant H 2 pressure, increased with increasing concentration of MAA. This behavior of optical yield was satisfactorily explained by assuming the Langmuir-Hinshelwoodtype rate equations for the reactions on both (i.e., selective and nonselective) sites where MAA and H 2 are adsorbed competitively on each site and where the adsorption equilibrium constant of MAA on nonselective sites is larger than that on selective sites. Some unsaturated compounds added to the reaction mixture considerably increased the optical yield of MHB. This effect is attributable to the decrease of reaction rate on nonselective sites due to the competitive adsorption of reactants and the added compound.

Enantioselectivity of tartaric acid-modified Ni-Al2O3 catalysts

Abstract Effects of the preparation conditions on the properties of precipitated Ni-Al2O3 (1:1) catalysts precursors were studied using thermogravimetric analysis (TGA). The larger part of the nickel species on alumina, having no interaction with the support, is readily reduced and yields large nickel crystallites, while the remaining smaller part of the nickel species, having strong interactions with the support, has a lower reducibility and yields smaller crystallites. The reducibility of only the latter species is affected by the preparation conditions. The resulting bimodal size distribution of nickel crystallites on alumina explains the low activity and enantioselectivity of modified Ni-Al2O3 catalysts prepared with sodium carbonate. A small amount of Fe salt precipitated on the support prior to the precipitation of the Ni salt increases the enantioselectivity of the catalyst, probably as a result of blocking the sites having strong metal-support interactions.