Stereoselective hydrogenation of (−)-menthone and (+)-isomenthone mixture using nickel catalysts

The catalytic hydrogenation of an optically active mixture of (−)-menthone and (+)-isomenthone was studied. The catalysts Raney nickel and Ni/SiO₂ were used for these hydrogenations. Catalysts modified with (2R,3R)-(+)-tartaric acid were tested as well. Various non-equilibrium mixtures of isomers were produced by means of these reactions, especially mixtures containing the less stable menthol isomers, (+)-neomenthol and (+)-neoisomenthol. (−)-Menthol was produced during these reactions to a limited extent, the production of (−)-isomenthol was barcly existent. Isomerization of (−)-menthone and (+)-isomenthone occurred during these reactions. Isomerizations among individual isomers were barely detectable. The catalysts used showed a very low activity under the given reaction conditions.     

From local adsorption stresses to chiral surfaces: (R,R)-tartaric acid on Ni(110).

The chiral molecule (R,R)-tartaric acid adsorbed on nickel surfaces creates highly enantioselective heterogeneous catalysts, but the nature of chiral modification remains unknown. Here, we report on the behavior of this chiral molecule with a defined Ni(110) surface. A combination of reflection absorption infrared spectroscopy, scanning tunneling microscopy, and periodic density functional theory calculations reveals a new mode of chiral induction. At room temperatures and low coverages, (R,R)-tartaric acid is adsorbed in its bitartrate form with two-point bonding to the surface via both carboxylate groups. The molecule is preferentially located above the 4-fold hollow site with each carboxylate functionality adsorbed at the short bridge site via O atoms placed above adjacent Ni atoms. However, repulsive interactions between the chiral OH groups of the molecule and the metal atoms lead to severely strained adsorption on the bulk-truncation Ni(110) surface. As a result, the most stable adsorption structure is one in which this adsorption-induced stress is alleviated by significant relaxation of surface metal atoms so that a long distance of 7.47 A between pairs of Ni atoms can be accommodated at the surface. Interestingly, this leads the bonding Ni atoms to describe a chiral footprint at the surface for which all local mirror symmetry planes are destroyed. Calculations show only one chiral footprint to be favored by the (R,R)-tartaric acid, with the mirror adsorption site being unstable by 6 kJ mol(-1). This energy difference is sufficient to enable the same local chiral reconstruction and motif to be sustained over 90% of the system, leading to an overall highly chiral metal surface.     

Temperature programmed reduction of silica supported nickel catalysts

Nickel oxide promoted catalysts are prepared by simple precipitation, precipitation from homogeneous solution and impregnation methods and their reduction behavior is monitored with temperature programmed reduction (TPR) technique. The effect of different parameters such as metal loading, method of preparation and heat treatment temperature are also observed on the reducibility of the catalysts. It is observed that reduction temperature increases with the increase of calcination temperature. Results indicate that the interactions between nickel oxide and silica begin with the increase of calcination temperature which leads to the formation of nickel hydrosilicates and are responsible for high temperature reduction peaks.     

The kinetics of enantioselective hydrogenation of methyl acetoacetate using a modified Raney nickel catalyst

The kinetics of enantioselective hydrogenation of methyl acetoacetate using Raney nickel modified by (2R,3R)-(+)-tartaric acid were studied, thereby focusing on the effects of the reaction conditions on the enantioselectivity. Reactions were carried out in a liquid phase under atmospheric and increased hydrogen pressure. The reaction course was described by the exponential kinetics model and by Langmuir-Hinshelwood kinetics assuming the existence of two types of active sites on the catalyst surface, selective and non-selective. Using Langmuir-Hinshelwood kinetics, the acquired parameters were used for discussion of the effects of the reaction conditions on the enantioselectivity and the mechanism of the enantioselective hydrogenation.     

Reinforced nickel and nickel-platinum catalysts for performing the thermally coupled reactions of methane steam reforming and hydrogen oxidation

The formation of composite nickel and nickel-platinum catalysts reinforced with steel gauze was studied. The catalysts were prepared by sintering powdered nickel metal and a supported nickel catalyst (GIAP-3 or NIAP-18) with a chromium oxide additive in the case of nickel-containing composite catalysts or by sintering powdered nickel, aluminum, and a supported platinum catalyst in the case of catalysts containing nickel-platinum. With the use of electron microscopy, mercury porosimetry, and X-ray electron probe microanalysis, it was found that a metal matrix, in the pores of which supported catalyst particles were distributed, was formed in the composite catalysts. The reinforced nickel catalysts prepared were active in the reaction of methane steam reforming, and the catalysts containing nickel-platinum were active in the reaction of hydrogen oxidation. An increase in the activity of reinforced nickel catalysts in the course of the reaction was found. It is believed that the increase of the activity was due to the reduction of nickel oxide from an inactive difficult-to-reduce oxide film containing nickel and chromium oxides under the action of the reaction atmosphere.     

Ordered mesoporous silicates of MCM-41 type as support of pt catalysts for the enantioselective hydrogenation of 1-phenyl-1,2-propanedione

Summary Platinum catalysts (1 wt.%) supported on MCM-41 type and SiO₂have been prepared, characterized and evaluated in the enantioselective hydrogenation of 1-phenyl-1,2-propanedione at 298 K and 20 bar of hydrogen pressure, using cinchonidine (CD) as chiral modifier. Chemisorption and TEM results revealed that both catalysts posses similar metal dispersion, however, significant differences in the catalytic behavior were observed. With dichloromethane as solvent, high hydrogenation rates and ee values around 47% were obtained for the Pt/MCM-41 catalyst. This fact is attributed to a confinement effect. The initial reaction rate is strongly dependent on the CD concentration, and the reaction rate (or ee) vsCD concentration plot exhibits bell-type curves. The main products were (R) -1-hydroxy-1-phenylpropanone and (S) -1-hydroxy-1-phenylpropanone.</o:p>     

Activation of nickel–chromium hydrogenation catalysts with hydrogen

The kinetics of the reduction of nickel cations in nickel oxide and nickel–chromium catalysts whose oxide precursors have different structures has been investigated by thermal analysis. The reduction of nickel oxide with a hydrogen-containing gas takes place at 250–330°C. The apparent activation energy of this reaction is about 88 kJ/mol. The introduction of up to 30 at % chromium cations into the nickel oxide structure shifts the reduction temperature of nickel in the oxide phase to 300–450°C and increases the apparent activation energy of the reduction of nickel cations to ～108 kJ/mol. The introduction of 67 at % chromium into nickel oxide results in the formation of an oxide precursor with a spinel structure. The apparent activation energy of the reduction of nickel cations in this spinel is about 163 kJ/mol. The results of this study can be used in optimizing the composition of Ni-containing hydrogenation catalysts and their activation and operation conditions.     

Solid-phase synthesis of homogeneous ruthenium catalysts on silica for the continuous asymmetric transfer hydrogenation reaction

The solid-phase synthesis of new asymmetric transfer hydrogenation catalysts as well as the use of these silica supported systems in batch and flow reactors is reported. The ruthenium complex of NH-benzyl-(1R,2S)-(-)-norephedrine covalently tethered to silica showed a high activity and enantioselectivity in the reduction of acetophenone. In three consecutive batchwise catalytic runs, we obtained ee values of 88%. In a continuous flow reactor, a very constant catalytic activity was observed; no catalyst deactivation occurred over a period of one week. This has been ascribed to successful site isolation. Using optimized conditions in this flow reactor, the ee was as high as 90% at 95% conversion. The supported catalysts generally show the same trend in catalyst performance as in solution. The viability of our approach was further shown in one example, the ruthenium(II) complex of (1S,2R)-(+)-2-amino-1,2-diphenylethanol, for which an enantiomeric excess of 58% was observed, which is nearly three times higher than its homogeneous analogue.     

Kinetics of carbon monoxide methanation on nickel catalysts

The kinetics of CO methanation in excess H₂ on CaO- and CeO₂-doped nickel catalysts supported on Al₂O₃ and TiO₂ was studied at atmospheric pressure in a temperature range of 180–240°C. It was found that the same rational fractional rate equation corresponding to the reaction taking place at high surface coverages, is valid for all of the catalysts. The activity of nickel catalysts in the methanation reaction and their adsorption capacity with respect to reaction mixture components depend on the nature of the support and dopants.     

Hydrogenolysis of lignosulfonate into phenols over heterogeneous nickel catalysts

We report a strategy for the catalytic conversion of lignosulfonate into phenols over heterogeneous nickel catalysts. Aryl-alkyl bonds (C-O-C) and hydroxyl groups (-OH) are hydrogenated to phenols and alkanes, respectively, without disturbing the arenes. The catalyst is based on a naturally abundant element, and is recyclable and reusable.     

Complex study of nickel skeleton catalysts: V. Study of novel non-pyrophoric nickel skeleton catalysts by derivatograph

The structure and properties of non-pyrophoric skeleton catalysts prepared from NiSi, NiAlSi, NiMg and NiZn alloys have been studied—apart from other thermal methods—by means of the derivatograph.Our experimental results have contributed to the explanation of the non-pyrophoric behaviour of these catalysts. We demonstrated that the desorption of the hydrogen content in our catalysts is not accompanied by the oxidation of active nickel. This oxidation takes place only at higher temperatures, above 200°C, at a rate proportional to the amount of active nickel.Other constituents of the catalysts (adsorbed water, hydroxide content) were also determined from the experimental data. The outstandingly high Mg(OH)₂ content of the NiMg catalyst indicates that its structure is dissimilar: Mg(OH)₂ also acts as support for the catalyst.     

还原方式及还原温度对甲烷部分氧化镍催化剂结构和反应性能的影响

采用H2 TPR、TEM及活性评价等手段,考察了还原方式（等温和程序升温还原）及还原温度对不同温度（550℃和950℃）焙烧制备的镍基催化剂结构和甲烷部分氧化反应性能的影响。结果表明,与程序升温还原方式相比,等温还原的催化剂中镍物种的还原度较低、Ni晶粒度较小。还原方式对550℃焙烧制备的催化剂（POM-1）的甲烷部分氧化反应性能影响不明显,但等温还原的催化剂反应过程中床层温度较低。随着等温还原温度的提高,POM-1催化剂的镍还原度有所降低,而950℃焙烧制备的催化剂（POM-5）还原度略有增加,且具有较小的镍晶粒。随着等温还原温度的提高,POM-1催化剂反应性能无明显差异,但床层热点温度提高;POM-5催化剂反应性能随还原温度的提高而提高,且床层温度呈现降低趋势。通过分析发现,催化剂床层温度与催化剂镍晶粒大小密切相关,较小的镍晶粒利于床层热点温度的降低,这与较大镍晶粒利于甲烷完全氧化反应有关。     

载体对Ni_2P催化剂加氢脱氮反应性能的影响

使用TiO2、Al2O3以及TiO2-Al2O3复合载体考察了载体对磷化镍催化剂活性相和加氢脱氮性能的影响。不同钛铝原子比的TiO2-Al2O3复合载体采用原位-溶胶凝胶法制备,负载的磷化镍催化剂采用等体积浸渍法和H2原位还原法制备。以喹啉为模型化合物在固定床反应器上对催化剂的加氢脱氮性能进行评价,采用XRD、N2吸附、TEM和H2-TPR等技术对催化剂和载体进行了表征。结果表明,制成的复合载体基本保留了最初引入的γ-Al2O3的孔特征,分散在γ-Al2O3表面的TiO2以锐钛矿晶型存在。不同载体对催化剂的H2还原行为有显著影响,所形成的活性物种也不相同。Al2O3中引入TiO2可以减弱P物种和Al2O3之间的相互作用,有利于Ni2P活性相的生成和催化活性的提高。当Ti/Al的原子比为1∶8时,Ni2P/TiO2-Al2O3催化剂比Ni2P/TiO2、Ni2P/Al2O3催化剂具有更高的加氢脱氮活性。     

Reinforced nickel catalysts for steam reforming of methane to synthesis gas

XRD, mercury porosimetry, low-temperature nitrogen adsorption and electron microscopy were used to study peculiarities of the formation of reinforced composite nickel catalysts. The catalysts were prepared by sintering powdered metallic nickel with a supported nickel catalyst (GIAP-3 or NIAP-18) applied to a reinforcing stainless steel gauze. It was found that a metal matrix, in the pores of which supported catalyst particles were distributed, was formed in the composite catalysts. The NIAP-18-based catalyst exceeded the GIAP-3-based catalyst in activity toward the methane steam reforming. The NIAP-18-based catalyst was as active as the Cr₂O₃-doped NIAP-18-based catalyst, but showed a worse coke-resistance. A chromium oxide additive increased the activity of the GIAP-3-based catalyst.     

异三尖杉酯碱侧链酸的合成

本文报道了异三尖杉酯碱侧链酸(3)的立体选择性合成。(R,R)-(+)-酒石酸先制成酒石酸二甲酯缩丙酮(8), 然后经烷基化、构型转换、催化加氢、碱性水解、部分酯化和酸性水解, 首次成功地得到了预期产物3。     

Nickel catalysts based on porous nickel for methane steam reforming

The influence of synthesis conditions on the phase composition and texture of porous nickel supports as plates with a magnesium oxide underlayer were investigated by X-ray diffraction, low-temperature nitrogen absorption, and electron microscopy combined with X-ray microanalysis. Nickel catalysts supported on these plates were studied. Thermal treatment of Mg(NO₃)₂ in nitrogen yields a magnesium oxide underlayer with a small specific surface area (support I). The replacement of nitrogen with hydrogen leads to a larger surface area (support II). The formation of MgO is accompanied by the incorporation of Ni²⁺ cations from the oxide film into the underlayer. Upon subsequent reduction with hydrogen or under the action of the reaction medium, these cations form fine crystallites of nickel. The supports having an oxide underlayer show a higher activity in methane steam reforming than the initial metallic nickel. Nickel catalysts on supports I and II show similar activities. The activity of the catalysts was stable throughout 50-h-long tests; no carbon deposits were detected by TEM.     

Nucleation and particle growth in the preparation of silica-supported nickel catalysts by a two-step procedure

The mechanism of nucleation and growth of particles in the preparation of supported catalysts has been investigated in the case of the Ni/SiO₂ system. The separation of this two-step mechanism is achieved as follows:i) the “nickel nuclei” are prepared by ion-exchange or by impregnation followed by washing. They are in strong interaction with the support and act as anchoring sites for the metal particles.ii) The “nickel reservoir” constituted of nickel ion precursors and necessary for the nickel particle growth on the nuclei, is deposited by impregnation on the support. It is in weak interaction with the support and easily reducible. After temperature programmed reduction of the samples prepared by the above two-step procedure, the nickel particles are smaller and more homogeneous in size than those of catalysts prepared in one step by single impregnation of a pure silica support.     

Enantioselective epoxidation of linolenic acid catalysed by cytochrome P450(BM3) from Bacillus megaterium

Cytochrome P450(BM3), from Bacillus megaterium, catalyses the epoxidation of linolenic acid yielding 15,16-epoxyoctadeca-9,12-dienoic acid with complete regio- and moderate enantio-selectivity (60% ee). The absolute configuration of the product is tentatively assigned as 15(R),16(S)-. The Michaelis-Menten parameters kcat and Km for the reaction were determined to be 3126 +/- 226 min(-1) and 24 +/- 6 microM respectively.     

Electron microscopic study of the structure of nickel catalysts modified with heteropoly compounds

The state of the active phase on the surface of low-percentage nickel catalysts on carbon supports in the presence of new modifiers, mixed series 12 heteropoly compounds (HPC), was investigated. The presence of a modifier causes an increase in the dispersion of the nickel, formation of nickel-HPC associates on the surface of the support, and determines the high dispersion and thermal stability of the Ni particles in reducing medium. Modified nickel catalysts have higher selectivity for coal oils during liquid-phase hydrogenation of coal, and the process takes place with less gas formation.Deceased.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2705–2711, December, 1990.