Kinetics of 4-tert-butylphenol hydrogenation over rhodium

The kinetics of the liquid phase hydrogenation of 4-tert-butylphenol to form cis- and trans- 4-tert-butylcyclohexanol at 1.0–10.0 MPa and 40°C in isopropanol over a Rh catalyst has been studied. The kinetic behavior of this parallel system is described by a proposed reaction network. Keto-enol tautomeric transformation of adsorbed 4-tert-butyltetrahydrophenol and 4-tert-butylcyclohexanone is thought to be a key step, which governs the stereoselectivity of the overall complex reaction of alkylphenol hydrogenation.     

高分散[Pd-Pt]/C催化喹啉加氢制备1,2,3,4-四氢喹啉

利用双表面活性剂( Tween-20和Brij-35 )保护的方法,合成并表征了一系列[Pd-Pt]/C催化剂。将其应用于喹啉催化加氢制备1,2,3,4-四氢喹啉反应中,结果表明,5wt%[Pd-Pt(1:3)]/C的催化活性最高。优化反应参数,以乙醇为溶剂,初始底物浓度为2.4mol/L,在130℃, 2.5MPa下反应50min,喹啉转化率100%,1,2,3,4-四氢喹啉选择性100%。     

葡萄糖加氢制山梨醇纳米镍催化剂前驱体的研究

采用不同前驱体,硝酸镍、醋酸镍、氯化镍和草酸镍,十二烷基磺酸钠作为有机改性剂,浸渍法制备一系列纳米镍催化剂,并用XRD和TEM等技术对四组催化剂的物相、比表面积进行了表征。以葡萄糖加氢制山梨醇反应考察催化剂的活性,结果表明,纳米镍催化剂的活性与镍前驱体的性质,以及纳米镍的尺寸有着紧密关系。其中以氯化镍为前驱体制备的催化剂颗粒尺寸小且散度更高,在温度120℃,压力3.5 MPa下葡萄糖转化率可达93.9%,山梨醇的选择性可达90.1%,同时可循环使用3~4次。     

New approach for highly selective hydrogenation of phenol to cyclohexanone: Combination of rhodium nanoparticles and cyclodextrins

The effect of cyclodextrins on the activity and selectivity of a catalytic system based on rhodium nanoparticles stabilized by polyacrylic acid (PAA) in the hydrogenation of phenol in aqueous solution and ionic liquid was reported. It was found that the reaction medium and the nature of the cyclodextrin (CD) essentially affect the rate of reaction and the distribution of reaction products. The use of the system based on rhodium nanoparticles stabilized by cyclodextrins makes it possible to rapidly and efficiently prepare cyclohexanone from phenol with yields up to 100% under relatively mild conditions (1 h; T = 80°°C, p(H₂) = 10–40 bars).     

Selective hydrogenation of citral over gold nanoparticles on alumina

Gold nanoparticles have been supported on alumina by wet impregnation in the presence of sodium citrate and polyvinyl alcohol. The catalytic performance of these catalysts for the selective hydrogenation of 3,7-dimethyl-2,6-octadienal (citral) in the liquid phase has been evaluated. The presence of polyvinyl alcohol significantly improved the selectivity to cis-3,7-dimethyl-2,6-octadien-1-ol (nerol).     

Liquid phase hydrogenation of cyclohexene over Pt/aluminum borate catalyst

The hydrogenation of cyclohexene over Pt catalysts supported on alumina, activated carbon, and aluminum borate is investigated in a liquid phase batch reactor at a temperature of 60 °C and a hydrogen pressure of 1 atm. The dispersion of Pt metal on these catalysts was determined by hydrogen adsorption in gas volumetry. Under the conditions employed in this study, the aluminum borate-supported catalyst was found to possess the highest activity. This can be attributed to its high metal dispersion and high turnover frequency.     

Ethylene hydroformylation and carbon monoxide hydrogenation over modified and unmodified silica supported rhodium catalysts

Ethylene hydroformylation and carbon monoxide hydrogenation (leading to methanol and C₂-oxygenates) over Rh/SiO₂ catalysts share several important common mechanistic features, namely, CO insertion and metal–carbon (acyl or alkyl) bond hydrogenation. However, these processes are differentiated in that the CO hydrogenation also requires an initial CO dissociation before catalysis can proceed. In this study, the catalytic response to changes in particle size and to the addition of metal additives was studied to elucidate the differences in the two processes. In the hydroformylation process, both hydroformylation and hydrogenation of ethylene occurred concurrently. The desirable hydroformylation was enhanced over fine Rh particles with maximum activity observed at a particle diameter of 3.5 nm and hydrogenation was favored over large particles. CO hydrogenation was favored by larger particles. These results suggest that hydroformylation occurs at the edge and corner Rh sites, but that the key step in CO hydrogenation is different from that in hydroformylation and occurs on the surface. The addition of group II–VIII metal oxides, such as MoO₃, Sc₂O₃, TiO₂, V₂O₅, and Mn₂O₃, which are expected to enhance CO dissociation, leads to increased rates in CO hydrogenation, but only served to slow the hydroformylation process slightly without any effect on the selectivity. Similar comparisons using basic metals, such as the alkali and alkaline earths, which should enhance selectivity for insertion of CO over hydrogenation, increased the selectivity for the hydroformylation over hydrogenation as expected, although catalytic activity was reduced. Similarly, the selectivity toward organic oxygenates (a reflection of the degree of CO insertion) in CO hydrogenation was also increased.     

Homogeneous hydrogenation of dienes with rhodium complexes

Different Rh complex catalysts were compared for the hydrogenation of methyl sorbate and linoleate in the absence of solvents. At 100 C and 1 atm H₂ the following complexes, RhCl(Ph₃ P)₃ (Ph= phenyl), [RhClNBD]₂ (NBD=norbornadiene) and RhH(CO)(Ph₃P)₃, produced mainly methyltrans-2-hexenoate (34 to 56%). Their diene selectivity was not particularly high as they produced 14 to 41% methyl hexanoate. With RhCl(Ph₃ P)₃ constant ratios between rates of methyl sorbate disappearance and formation of methyltrans-2- andtrans-3-hexenoate indicate approximately the same activation energy for 1,2-addition of H₂ on the Δ4 double bond of methyl sorbate and for 1,4-addition to this substrate. In the hydrogenation of methyl linoleate with RhCl(Ph₃ P)₃, the kinetic curves were simulated by a scheme in which 1,2-reduction was more than twice as important as 1,4-addition of H₂ via conjugated diene intermediates. Although the complexes RhCl(CO)(Ph₃ P)₃ and [Rh(NBD)(diphos)]⁺PF₆ (diphos=diphosphine) were inactive in the hydrogenation of methyl sorbate, they catalyzed the hydrogenation of methyl linoleate at 100 C and 1 atm. Catalyst inhibition apparently was caused by stronger complex formation with methyl sorbate than with the conjugated dienes formed from methyl linoleate.     

Pt nanoparticles deposited over carbon nanotubes for selective hydrogenation of cinnamaldehyde

Two kinds of carbon nanotubes (CNTs) with different inner diameter (less than 10 nm: CNTs-1 and between 60 and 100 nm: CNTs-2) were used as catalyst supports. The platinum particles were simply deposited on the outside surface (CNTs-1) and inside (CNTs-2) and were easily reduced to Pt⁰ by refluxing. The catalysts exhibit high activities in the selective hydrogenation of cinnamaldehyde which contains both CC and CO bonds. But the selectivity of these two catalysts was quite different under same reaction conditions. The high selective hydrogenation of CO bond was observed over catalyst 3%Pt/CNTs-2, while the completely hydrogenation of both CC and CO bonds was found over catalyst 3%Pt/CNTs-1.     

The effect of support structure on CO2 hydrogenation over a rhodium catalyst supported on niobium oxide

The hydrogenation of CO₂ was investigated over a rhodium catalyst supported on niobium oxide at atmospheric pressure. Niobium oxide was prepared by the hydrolysis of niobium chloride and its crystallitic structure was controlled by calcination temperature. It was found that the activity was lower but the selectivity of C₂₊ hydrocarbons was higher for the and forms than for the and forms of the niobium oxide.     

Kinetics of nitrobenzene hydrogenation using a gel entrapped palladium catalyst

Palladium metal has been precipitated in a gel formed by the crosslinking polymerization of 2-hydroxyethylmethacrylate. The metal particles were found to have an average size of 14 nm. The dried polymer gel contained 1.38% Pd; it was crushed and sieved to give gel particles ca 200 μm in size. When the gel containing Pd was swollen by a solvent, catalytic activity toward the quantitative hydrogenation of nitrobenezene to aniline was observed. A detailed study of the kinetics of this hydrogenation revealed that at 101 kPa pressure and 31°C, resistance to the reaction was approximately equally divided between extra-particle mass transfer and the chemical activity of the Pd. The high activity of this novel catalyst is attributed to the large surface of the Pd and the extensive swelling of the gel by the reaction medium.     

高分散镍硅催化剂对喹啉催化加氢的性能

以硝酸镍和硅溶胶为原料,采用蒸氨水热法,制得了一系列负载量为10%(以镍在催化剂中的质量分数计,下同)的镍硅酸盐衍生的Ni-PS-AEH-x(x代表不同焙烧温度,下同)催化剂,并用于喹啉选择性加氢制取1,2,3,4-四氢喹啉。通过考察不同镍基催化剂的加氢性能,发现Ni-PS-AEH-400催化性能最好。通过考察反应条件的影响,确定最佳反应条件为:底物与金属镍投料比(物质的量之比,下同)为30∶1、反应温度100℃、氢气压力3MPa、反应时间120min,此时喹啉转化率为99.0%,1,2,3,4-四氢喹啉收率为95.4%。采用FTIR、XRD、TEM、N2吸附-脱附、H2-TPR和XPS对催化剂结构、组成、形貌进行了表征,结果表明:镍硅酸盐结构使Ni-PS-AEH-400比表面积大、镍纳米粒子分散均匀,活性中心与载体间的相互作用力强,使其在喹啉加氢反应中具有较浸渍法制备Ni/SiO2-IMP更优异的催化性能。     

Selective hydrogenation of nitrile butadiene rubber (NBR) with rhodium nanoparticles supported on carbon nanotubes at room temperature

Carbon-nanotubes (CNTs)-supported rhodium (Rh) nanoparticle catalysts were prepared by sequential sonication-assisted liquid phase exfoliation of multi-walled CNTs (MWCNTs) in the presence of polyvinylpyrrolidone (PVP), followed by microwave-assisted hydrothermal reduction of the supported Rh. The as-prepared Rh-PVP-MWCNT catalysts were applied in the selective hydrogenation of nitrile butadiene rubber. The catalyst had excellent activity even at room temperature and can be easily separated from the product.     

Phenol hydrogenation to cyclohexanone over palladium nanoparticles loaded on charming activated carbon adjusted by facile heat treatment

Selective phenol hydrogenation is a green approach to produce cyclohexanone. It still remains a big challenge to prepare efficient supports of the catalysts for the phenol hydrogenation via a simple and cost-effective approach. Herein, a facile approach was developed, i.e., direct calcination of activated carbon (AC) under argon at high temperature, to improve its structure and surface properties. The modified AC materials were supported with Pd nanoparticles (NPs) to fabricate the Pd/C catalysts. The as-prepared Pd/C600 catalyst exhibits superior catalytic performance in the phenol hydrogenation, and its turnover frequency (TOF) value is 199.2 h^-1, 1.31 times to that of Pd/C-raw. The Pd/C600 catalyst presents both better hydrophobicity and more structural defects, contributing to the improved dispersibility in the reaction solution (phenol-cyclohexane), the better Pd dispersion and the smaller Pd size, which result in the enhancement of the catalytic performance. Furthermore, the as-prepared Pd/C600 catalyst shows a good recyclability.     

Phenol hydrogenation to cyclohexanone over palladium nanoparticles loaded on charming activated carbon adjusted by facile heat treatment

Selective phenol hydrogenation is a green approach to produce cyclohexanone. It still remains a big challenge to prepare efficient supports of the catalysts for the phenol hydrogenation via a simple and cost-effective approach. Herein, a facile approach was developed, i.e., direct calcination of activated carbon (AC) under argon at high temperature, to improve its structure and surface properties. The modified AC materials were supported with Pd nanoparticles (NPs) to fabricate the Pd/C catalysts. The as-prepared Pd/C600 catalyst exhibits superior catalytic performance in the phenol hydrogenation, and its turnover frequency (TOF) value is 199.2 h⁻¹, 1.31 times to that of Pd/C-raw. The Pd/C600 catalyst presents both better hydrophobicity and more structural defects, contributing to the improved dispersibility in the reaction solution (phenol-cyclohexane), the better Pd dispersion and the smaller Pd size, which result in the enhancement of the catalytic performance. Furthermore, the as-prepared Pd/C600 catalyst shows a good recyclability.     

Catalytic activity of nickel nanoparticles in hydrogenation of p-nitrophenol to p-aminophenol

Nickel nanoparticles with different sizes and different structures were prepared by reducing nickel oxalate with hydrazine hydrate in the presence of citric acid, sodium dodecyl sulphonate, Tween 80, PEG 6000, and D-sorbitol as organic modifiers. The type of organic modifiers affected the size and the structure of the resultant nickel nanoparticles. The catalytic activities of the nickel nanoparticles increased with decreasing the particle size in the hydrogenation of p-nitrophenol to p-aminophenol. All the as-prepared nickel nanoparticles showed higher catalytic activity and selectivity than conventional Raney Ni catalyst.     

新型配体的NBR加氢催化体系

以含磷、氢、氧和硫元素的化合物为配体，分别与三氯化铑水合物形成配位催化剂，并以此对NBR进行加氢。结果表明：以含磷、氢、氮和硫元素的化合物为配体与铑金属离子的配位形成的催化剂对NBR加氢具有不同的活性；研制出用于NBR加氢的新型双配体催化剂（Rh－N－T），其加氢度可达96％以上，而且具有良好的空气稳定性。     

铑催化剂催化烯烃不对称加氢反应研究进展

不对称催化氢化反应具有完美的原子经济性和清洁高效等特点,是最受青睐的不对称合成方法之一。C=C、C=O、C=N的不对称加氢反应仍主要依赖过渡金属催化剂。过渡金属催化剂,尤其是铑催化剂,催化碳碳双键的不对称加氢反应仍是一个不断发展的领域。本文对近年来利用铑催化剂催化烯烃进行不对称氢化反应的研究进展进行了综述,着重介绍了铑-双膦配体催化体系催化烯烃不对称加氢反应的催化机理,以及铑催化剂在烯胺、不饱和羧酸及衍生物、烯醇酯和非官能团烯烃不对称氢化中的应用,并通过对现有文献的总结指出了今后铑催化剂催化烯烃氢化反应的研究重点,即:①铑-单膦配体催化烯烃不对称氢化反应的作用机理须待提出;②非官能化底物不对称催化氢化反应的手性配体亟待拓宽。     

Structure sensitivity in CO oxidation over rhodium

The rates of CO oxidation on the (110) and (111) planes of rhodium have been directly compared using a thermal molecular beam reactor. When the surfaces are largely covered by CO the reaction rate is the same on the two crystal planes. At higher temperatures, where CO desorbs and the surface becomes oxygen covered, the reaction becomes structure sensitive, being markedly faster on the more open (110) plane.