Reactivity of alkylphenols in liquid phase catalytic hydrogenation

The rate of liquid-phase hydrogenation of monoalkylphenols without solvent and in the absence of rate control by hydrogen diffusion to the catalyst indicate that the alkylphenol reactivity and the selectivity depend on the position and size of the alkyl substituent, affecting the electronic state of the aromatic ring and the charge on the carbonyl carbon atom of the ketone intermediate.

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Dimer formation of cinchonidine in liquid phase: relevance to the heterogeneous catalytic enantioselective hydrogenation of ethyl pyruvate

Literature data related to the possible dimer formation of cinchona alkaloids in the liquid phase are collected and analyzed. These data are correlated with experimental results obtained in the heterogeneous catalytic enantioselective hydrogenation of ethyl pyruvate. In this reaction, the addition of achiral tertiary amines (ATAs) resulted in an increase in both the reaction rates and enantioselectivity. The positive influence of ATAs was attributed to the suppression of dimer formation in aprotic solvents. The results of circular dichroism spectroscopy and ab initio calculations provided further proof for dimer formation. Four possible cinchonidine dimer configurations were found with approximate 11–13 kcal/mol stabilization energies.     

乙腈液相选择性加氢中Ni-B非晶态合金和Raney Ni催化性能的比较

以乙腈液相选择性加氢为目标反应，分别考察了超细Ni-B非晶态合金和Rancy Ni的催化性能，发现两者的质量比活性相似，但单位活性比表面积上前者的活性及对乙胺的选择性显著高于后者，乙胺的最高得率前者为67．6％后者为40％。通过催化剂的系统表征，结合考察乙腈加氢反应的动力学，从几何效应和电子效应两方面阐述了Ni-B非晶态合金催化性能与催化剂结构和表面电子态的关系。     

Bimetallic catalysts for hydrogenation in liquid phase

Activity and selectivity of bimetallic catalysts for two model reactions, citral hydrogenation in isopropanol and nitrate reduction in water, are reviewed on the basis of results obtained over bimetallic systems prepared in our laboratory, notably by redox techniques. The parent metal is generally a noble metal (Rh, Pd, Pt), while the additive is most often a non-noble metal (Ge, Sn, Cu…) whose oxidation state plays an important role in hydrogenation. Dramatic improvements of the selectivity to unsaturated alcohols are observed in citral hydrogenation with adequate deposition of the additive and pretreatment of the final catalyst. In nitrate reduction, the second metal essentially affects the first step of the process (conversion of nitrate to nitrite) but the global selectivity (limitation of NH₃ formation) may be significantly improved by tuning the couple parent metal–additive. Other aspects such as the choice of the support and the optimization of reaction conditions (temperature, pressure, pH effects in water) are also discussed.     

Electronic structure of tungsten carbide and its catalytic behavior

The different observations concerning the platinum-like electronic structure found in X-ray photoelectron spectra as contrasted by the platinum-unlike density of states detected by soft X-ray appearance potential spectroscopy is reconciled. The platinum-like catalytic activity of WC results from changes in the electron distribution when C is added to W; core level chemical shifts indicate electron transfer from W valence orbitals to C_2p orbitals.     

基于喹啉选择加氢反应的多相金属催化剂研究进展

喹啉选择加氢制备1,2,3,4-四氢喹啉是最为简便和可行的方法,后者是一种重要的精细化工中间体.本文综述了近10年基于喹啉及其衍生物选择加氢反应的多相金属催化剂研究进展,探讨了活性金属组分和载体对催化性能的影响.最后对该领域存在的问题和发展前景进行了总结和展望.     

A novel liquid system of catalytic hydrogenation

On the basis that endothermic aqueous-phase reforming of oxygenated hydrocarbons for H2 produc- tion and exothermic liquid phase hydrogenation of organic compounds are carried out under extremely close conditions of temperature and pressure over the same type of catalyst, a novel liquid system of catalytic hydrogenation has been proposed, in which hydrogen produced from aqueous-phase re- forming of oxygenated hydrocarbons is in situ used for liquid phase hydrogenation of organic com- pounds. The usage of active hydrogen generated from aqueous-phase reforming of oxygenated hy- drocarbons for liquid catalytic hydrogenation of organic compounds could lead to increasing the se- lectivity to H2 in the aqueous-phase reforming due to the prompt removal of hydrogen on the active centers of the catalyst. Meanwhile, this novel liquid system of catalytic hydrogenation might be a po- tential method to improve the selectivity to the desired product in liquid phase catalytic hydrogenation of organic compounds. On the other hand, for this novel liquid system of catalytic hydrogenation, some special facilities for H2 generation, storage and transportation in traditional liquid phase hydrogenation industry process are yet not needed. Thus, it would simplify the working process of liquid phase hy- drogenation and increase the energy usage and hydrogen productivity.     

Regularities of the heterogeneous catalytic hydrogenation of 5-vinyl-2-norbornene

Russian Chemical Bulletin - The liquid-phase hydrogenation of 5-ethenylbicyclo[2.2.1]hept-2-ene (5-vinyl-2-norbornene, VNE) in the presence of the palladium catalyst Pd/γ-Al2O3 (PC-25) in an...     

Non-contact biomimetic mechanism for selective hydrogenation of nitroaromatics on heterogeneous metal nanocatalysts

While the enzymatic reduction of unsaturated compounds usually has high specificity, highly selective reduction processes are hardly realized by heterogeneous industrial catalysts, which is critical for the green production of many fine chemicals. Here, we report an unexpected discovery of a biomimetic behavior of dicyandiamide(DICY)-modified Pt nanocatalysts for the green hydrogenation of a wide range of nitroaromatics. We demonstrate that the surface modification by DICY not only prevents the ...     

Role of homogeneous steps in the heterogeneous catalytic hydrogenation of substituted 2-Nitroazobenzenes

The homogeneous reactions of nitrohydrazo derivatives contribute substantially to the benzotriazole selectivity of the hydrogenation of substituted 2-hydroxynitroazobenzene. The rate of the homogeneous steps is governed by the solvent composition rather than by the substituent in the starting nitroazobenzene. An increase in pH in both aqueous and aqueous-alcohol solutions increases the rate constants of the homogeneous reactions of various substituted nitrohydrazo derivatives and considerably enhances the selectivity of the reaction with respect to the compounds containing a triazole ring. A kinetic model has been suggested to qualitatively describe the influence of the pH value of the medium on the rate of the cyclization of substituted 2′-hydroxy-5′-hydrazobenzenes into the corresponding benzotriazole N-oxides.     

焙烧温度对CuMgAl催化剂催化糠醛气相加氢制糠醇性能的影响

采用分步沉淀过程制得质量比m(CuO)∶m(MgO)∶m(Al_2O_3)为25∶26∶49的CuMgAl类水滑石前驱体,经过不同温度焙烧制得CuMgAl-t催化剂。通过BET、热重、XRD、H_2-TPR和CO_2-TPD对催化剂进行表征,在固定床中考察CuMgAl-t催化剂催化糠醛气相加氢制糠醇的性能。结果表明,焙烧温度影响催化剂活性、稳定性及对产物的选择性,低温焙烧的催化剂经还原后可获得较多活性中心,高温焙烧的催化剂表面具有更多的碱性位,CuMgAl催化剂经450℃焙烧表面存在适宜的活性中心和碱性位。在常压、反应温度180℃、氢醛物质的量比5∶1、糠醛体积空速0.3h~(-1)的条件下,CuMgAl-450催化剂上糠醛的转化率和糠醇的选择性分别达到98.64%和97.66%。     

Homogeneous catalytic hydrogenation of liquid carboxylated nitrile rubber

Homogeneous catalytic hydrogenation of olefinic bonds in liquid carboxylated nitrile rubber (L-XNBR) has been carried out selectively in the presence of nitrile and carboxyl functionality using a six-membered cyclopalladate complex of 2-benzoyl pyridine as catalyst. The degree of hydrogenation has been calculated from IR and NMR spectroscopic studies. For example, 68% hydrogenation has been obtained for a sample (containing 0.057 carboxyl equivalent/100 g and 26.1% acrylonitrile) under 2.7 MPa hydrogenation pressure, 0.18 mmol/L catalyst, at 333 K for 1 h in acetone solution. The overall extent of hydrogenation depends on the catalyst-to-double-bond ratio. The kinetics of hydrogenation of L-XNBR has been investigated. The reaction exhibits a pseudo-first order dependence on the concentration of the substrate. The rate constant of the reaction is reduced by the increase in carboxyl and nitrile content of the polymer. The effect of temperature on reaction kinetics has also been studied and the activation energy of hydrogenation of L-XNBR is 20.2 kJ/mol. Intrinsic viscosity of the polymer remains unchanged during the reaction. A significant lowering of the glass transition temperature and improvement of thermal stability have been observed on hydrogenation. © 1992 John Wiley & Sons, Inc.     

Novel electrochemical heterogeneous catalytic reactor for organic pollutant abatement

Taking nitrobenzene as a model, electrochemical heterogeneous catalytic degradation of organic pollutant is investigated using a novel electrochemical heterogeneous catalytic reactor coupled by three-dimensional electrode with heterogeneous catalytic reactor. The nitrobenzene removal efficiencies considerably depend on the applied potential, initial pH, and the concentration of the supporting electrolyte. The results show that, with catalyst the nitrobenzene removal efficiencies are higher than that of control (without catalyst). The efficiency of ferrous catalyst is the best for nitrobenzene removal especially. It is clear that the reaction of electro-oxidation is promoted by the catalyst. A possible mechanism of nitrobenzene degradation is deduced based on products. Published in Russian in Elektrokhimiya, 2007, Vol. 43, No. 3, pp. 313–318. The text was submitted by the authors in English.     

Carbon dioxide-expanded liquid substrate phase: an effective medium for selective hydrogenation of cinnamaldehyde to cinnamyl alcohol

It has been shown that CO(2)-expanded cinnamaldehyde liquid phase is a unique and effective medium for cinnamaldehyde hydrogenation to cinnamyl alcohol, due to interactions between the C[double bond, length as m-dash]O group of the substrate and CO(2) molecules and increased solubility of H(2).     

An active and selective heterogeneous catalytic system for Michael addition

Potassium fluoride doped natural zeolite was found to be an efficient and selective solid base catalyst for 1,4-Michael addition. The catalyst is easily prepared and the workup procedure simplified by simple filtration.All products were obtained in high yields as well as short reaction times.     

An efficient heterogeneous catalytic system for chemoselective hydrogenation of unsaturated ketones in aqueous medium

A highly chemoselective and green heterogeneous catalytic system of immobilized Ru(II)–phenanthroline complexes on amino functionalised MCM-41 material for the chemoselective hydrogenation of unsaturated ketones to unsaturated alcohols is demonstrated using water as a solvent. The XRD and FTIR spectra show the highly ordered hexagonal nature of the MCM-41, even after encapsulation of the ruthenium complex. The complex retains its configuration after anchoring, as was confirmed by FTIR and UV–Vis analysis. The detailed reaction parametric effect was studied for the hydrogenation of 3-methylpent-3-en-2-one to achieve complete conversion up to >99% chemoselectivity of 3-methylpent-3-en-2-ol. The anchored heterogeneous catalysts were recycled effectively and reused five times with marginal changes in activity and selectivity. The use of water as a solvent not only afforded high activity for the hydrogenation reaction compared to organic solvents, but also afforded a green process.     

氯代苯胺液相催化加氢合成环己酮

提出了一种催化降解氯代苯胺高选择性合成环己酮的技术.在La修饰Pd/Al2O3催化剂作用下,通过催化加氢的方法实现了由多氯代苯胺(2,4,6-三氯苯胺和2,4,-二氯苯胺)高选择性地合成环己酮(不含环己醇).在优化的反应条件下,2,4,6-三氯苯胺加氢生成环己酮的转化率和选择性分别为100%和98.6%(没有检测到环己醇);2,4,-二氯苯胺加氢生成环己酮的转化率和选择性均为100%.氯代苯胺在Pd/La-Al2O3催化剂表面首先发生加氢脱氯/N-甲基化等反应生成苯胺、N-甲基苯胺和N,N-二甲基苯胺等中间产物,随后这些中间产物发生苯环加氢、氨基水解/醇解等反应得到环己酮;氯代苯胺上Cl元素的存在和体系中水的含量是影响环己酮选择性的重要因素.     

Competitive hydrogenation of binary olefin mixtures in the liquid phase

The effect of a series of alcohol solvents on the selectivity of the competitive catalytic hydrogenation of 1-hexene and 2-methyl-3-butene-2-ol on Pt/SiO₂ catalyst has been investigated. With increasing molecular mass of the alcohol, the rate of hydrogenation of 1-hexene becomes relatively preferred; the same was observed also with branched alcohols compared with those having a straight chain. Systems were found in which the degree of coating of the platinum catalyst with copper affected (or did not affect) the selectivity of the competitive hydrogenation of pairs of olefinic substrates.

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