- One-pot dual catalysis for the hydrogenation of heteroarenes and arenes
-
A simple dinuclear monohydrido bridged ruthenium complex [{(η6-p-cymene)RuCl}2(μ-H-μ-Cl)] acts as an efficient and selective catalyst for the hydrogenation of various heteroarenes and arenes. The nature of the catalytically active species was investigated using a combination of techniques including in situ reaction monitoring, kinetic studies, quantitative poisoning experiments and electron microscopy, evidencing a dual reactivity. The results suggest that the hydrogenation of heteroarenes proceeds via molecular catalysis. In particular, monitoring the reaction progress by NMR spectroscopy indicates that [{(η6-p-cymene)RuCl}2(μ-H-μ-Cl)] is transformed into monomeric ruthenium intermediates, which upon subsequent activation of dihydrogen and hydride transfer accomplish the hydrogenation of heteroarenes under homogeneous conditions. In contrast, carbocyclic aryl motifs are hydrogenated via a heterogeneous pathway, by in situ generated ruthenium nanoparticles. Remarkably, these hydrogenation reactions can be performed using molecular hydrogen under solvent-free conditions or with 1,4-dioxane, and thus give access to a broad range of saturated heterocycles and carbocycles while generating no waste.
- Chatterjee, Basujit,Kalsi, Deepti,Kaithal, Akash,Bordet, Alexis,Leitner, Walter,Gunanathan, Chidambaram
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p. 5163 - 5170
(2020/09/07)
-
- Selective hydrogenation of fluorinated arenes using rhodium nanoparticles on molecularly modified silica
-
The production of fluorinated cyclohexane derivatives is accomplished through the selective hydrogenation of readily available fluorinated arenes using Rh nanoparticles on molecularly modified silica supports (Rh?Si-R) as highly effective and recyclable catalysts. The catalyst preparation comprises grafting non-polar molecular entities on the SiO2 surface generating a hydrophobic environment for controlled deposition of well-defined rhodium particles from a simple organometallic precursor. A broad range of fluorinated cyclohexane derivatives was shown to be accessible with excellent efficacy (0.05-0.5 mol% Rh, 10-55 bar H2, 80-100 °C, 1-2 h), including industrially relevant building blocks. Addition of CaO as scavenger for trace amounts of HF greatly improves the recyclability of the catalytic system and prevents the risks associated to the presence of HF, without compromising the activity and selectivity of the reaction.
- Bordet, Alexis,Emondts, Meike,Kacem, Souha,Leitner, Walter
-
p. 8120 - 8126
(2020/12/28)
-
- Effects of steam on toluene hydrogenation over a Ni catalyst
-
The catalytic toluene hydrogenation over Ni/SiO2 was carried out using H2 or a H2/H2O mixture. The toluene conversion and MCH selectivity were evaluated under partial steam pressures 0?10 kPa, at H2/t
- Atsumi, Ryosuke,Kobayashi, Keisuke,Xieli, Cui,Nanba, Tetsuya,Matsumoto, Hideyuki,Matsuda, Keigo,Tsujimura, Taku
-
-
- Titanium(III)-Oxo Clusters in a Metal-Organic Framework Support Single-Site Co(II)-Hydride Catalysts for Arene Hydrogenation
-
Titania (TiO2) is widely used in the chemical industry as an efficacious catalyst support, benefiting from its unique strong metal-support interaction. Many proposals have been made to rationalize this effect at the macroscopic level, yet the underlying molecular mechanism is not understood due to the presence of multiple catalytic species on the TiO2 surface. This challenge can be addressed with metal-organic frameworks (MOFs) featuring well-defined metal oxo/hydroxo clusters for supporting single-site catalysts. Herein we report that the Ti8(μ2-O)8(μ2-OH)4 node of the Ti-BDC MOF (MIL-125) provides a single-site model of the classical TiO2 support to enable CoII-hydride-catalyzed arene hydrogenation. The catalytic activity of the supported CoII-hydride is strongly dependent on the reduction of the Ti-oxo cluster, definitively proving the pivotal role of TiIII in the performance of the supported catalyst. This work thus provides a molecularly precise model of Ti-oxo clusters for understating the strong metal-support interaction of TiO2-supported heterogeneous catalysts.
- Ji, Pengfei,Song, Yang,Drake, Tasha,Veroneau, Samuel S.,Lin, Zekai,Pan, Xiandao,Lin, Wenbin
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p. 433 - 440
(2018/01/17)
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- Effect of the Crystallographic Phase of Ruthenium Nanosponges on Arene and Substituted-Arene Hydrogenation Activity
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Identifying crystal structure sensitivity of a catalyst for a particular reaction is an important issue in heterogeneous catalysis. In this context, the activity of different phases of ruthenium catalysts for benzene hydrogenation has not yet been investigated. The synthesis of hcp and fcc phases of ruthenium nanosponges by chemical reduction method has been described. Reduction of ruthenium chloride using ammonia borane (AB) and tert-butylamine borane (TBAB) as reducing agents gave ruthenium nanosponge in its hcp phase. On the other hand, reduction using sodium borohydride (SB) afforded ruthenium nanosponge in its fcc phase. The as prepared hcp ruthenium nanosponge was found to be catalytically more active compared to the as prepared fcc ruthenium nanosponge for hydrogenation of benzene. The hcp ruthenium nanosponge was found to be thermally stable and recyclable over several cycles. This self-supported hcp ruthenium nanosponge shows excellent catalytic activity towards hydrogenation of various substituted benzenes. Moreover, the ruthenium nanosponge catalyst was found to bring about selective hydrogenation of aromatic cores of phenols and aryl ethers to the respective alicyclic products without hydrogenolysis of the C?O bond.
- Ghosh, Sourav,Jagirdar, Balaji R.
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p. 3086 - 3095
(2018/05/29)
-
- Nanoscale Ziegler catalysts based on bis(acetylacetonate)nickel in the arene hydrogenation reactions
-
The turnover frequencies of catalytic systems based on Ni(acac)2–AlEt3 or AlEt2(OEt) in the hydrogenation of benzene and its methyl-substituted homologs (toluene, three isomers of xylene, and 1,3,5-trimethylbenzene) have been determined at temperatures of 80–120 °C, initial PH2 = 15 bar, and different ratios of Al/Ni. The size and nature of the nanoparticles forming in the systems based on Ni(acac)2–AlEt3 or AlEt2(OEt) under the benzene hydrogenation condition shave been resolved by high-resolution electron microscopy and X-ray microanalysis. This study included the performance of competitive hydrogenation reactions of benzene with toluene or three xylene isomers. The relative adsorption constants of toluene and three xylene isomers have been determined and the stereochemistry of the hydrogen addition to the arene ring has also been elucidated.
- Titova, Yuliya Yu.,Schmidt, Fedor K.
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p. 105 - 114
(2017/09/05)
-
- One-step hydroprocessing of fatty acids into renewable aromatic hydrocarbons over Ni/HZSM-5: Insights into the major reaction pathways
-
For high caloricity and stability in bio-aviation fuels, a certain content of aromatic hydrocarbons (AHCs, 8-25 wt%) is crucial. Fatty acids, obtained from waste or inedible oils, are a renewable and economic feedstock for AHC production. Considerable amounts of AHCs, up to 64.61 wt%, were produced through the one-step hydroprocessing of fatty acids over Ni/HZSM-5 catalysts. Hydrogenation, hydrocracking, and aromatization constituted the principal AHC formation processes. At a lower temperature, fatty acids were first hydrosaturated and then hydrodeoxygenated at metal sites to form long-chain hydrocarbons. Alternatively, the unsaturated fatty acids could be directly deoxygenated at acid sites without first being saturated. The long-chain hydrocarbons were cracked into gases such as ethane, propane, and C6-C8 olefins over the catalysts' Br?nsted acid sites; these underwent Diels-Alder reactions on the catalysts' Lewis acid sites to form AHCs. C6-C8 olefins were determined as critical intermediates for AHC formation. As the Ni content in the catalyst increased, the Br?nsted-acid site density was reduced due to coverage by the metal nanoparticles. Good performance was achieved with a loading of 10 wt% Ni, where the Ni nanoparticles exhibited a polyhedral morphology which exposed more active sites for aromatization.
- Xing, Shiyou,Lv, Pengmei,Wang, Jiayan,Fu, Junying,Fan, Pei,Yang, Lingmei,Yang, Gaixiu,Yuan, Zhenhong,Chen, Yong
-
p. 2961 - 2973
(2017/02/05)
-
- Upgrading of aromatic compounds in bio-oil over ultrathin graphene encapsulated Ru nanoparticles
-
Fast pyrolysis of biomass for bio-oil production is a direct route to renewable liquid fuels, but raw bio-oil must be upgraded in order to remove easily polymerized compounds (such as phenols and furfurals). Herein, a synthesis strategy for graphene encapsulated Ru nanoparticles (NPs) on carbon sheets (denoted as Ru@G-CS) and their excellent performance for the upgrading of raw bio-oil were reported. Ru@G-CS composites were prepared via the direct pyrolysis of mixed glucose, melamine and RuCl3 at varied temperatures (500-800 °C). Characterization indicated that very fine Ru NPs (2.5 ± 1.0 nm) that were encapsulated within 1-2 layered N-doped graphene were fabricated on N-doped carbon sheets (CS) in Ru@G-CS-700 (pyrolysis at 700 °C). And the Ru@G-CS-700 composite was highly active and stable for hydrogenation of unstable components in bio-oil (31 samples including phenols, furfurals and aromatics) even in aqueous media under mild conditions. This work provides a new protocol to the utilization of biomass, especially for the upgrading of bio-oil.
- Shi, Juanjuan,Zhao, Mengsi,Wang, Yingyu,Fu, Jie,Lu, Xiuyang,Hou, Zhaoyin
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supporting information
p. 5842 - 5848
(2016/05/24)
-
- Aromatic ring hydrogenation catalysed by nanoporous montmorillonite supported Ir(0)-nanoparticle composites under solvent free conditions
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Ir(0)-nanoparticles (Ir-NPs) were synthesized into the nanopores of modified montmorillonite clay by incipient wetness impregnation of IrCl3 followed by reduction with ethylene glycol. The activation of the montmorillonite clay was carried out by treatment with HCl under controlled conditions to increase the surface area by generating nanopores which act as host for the metal nanoparticles. The synthesized Ir-NP-montmorillonite composites were characterized by N2-sorption, powder XRD, SEM, EDS, TEM, XPS, etc. The composites exhibit high surface area of 327 m2 g-1 and the Ir-NPs with size around 4 nm are uniformly distributed on the support. The Ir-NPs show efficient catalytic activity in aromatic ring hydrogenation under solvent free conditions with maximum conversion up to 100% and Turn Over Frequency (TOF) up to 79 h-1. The catalyst can be easily separated by simple filtration and remained active for several runs without significant loss of catalytic efficiency.
- Das, Prabin,Sarmah, Podma Pollov,Borah, Bibek Jyoti,Saikia, Lakshi,Dutta, Dipak Kumar
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p. 2850 - 2855
(2016/03/22)
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- Hydrogenation of lignin-derived phenolic compounds over step by step precipitated Ni/SiO2
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The harsh reaction conditions for the valorization of lignin-derived phenolic compounds considerably limit the efficient utilization of the lignin derivatives. Here, we put forward a high efficient and selective hydrogenation process for phenolic compounds at a mild condition over step by step precipitated Ni/SiO2 catalyst. The properties of the Ni/SiO2 catalysts by different preparation methods were detailedly compared using various characterization measurements. Catalytic activity of the catalysts was tested by the hydrogenation of guaiacol, and the results showed that guaiacol could be completely converted into cyclohexanol with 99.9% selectivity at 120 °C, 2 MPa H2 atmosphere for 2 h. Other typical lignin-derived phenolic compounds also had excellent hydrogenation performance and great energy efficiency. Catalyst characterization results demonstrated that the high catalytic activity of the step by step precipitated Ni/SiO2 was mainly ascribed to its polyporous spherical structure, which led to the large specific surface area and high nickel dispersion. The appropriate acidity of the catalyst also promoted the catalytic performance significantly. Furthermore, the catalyst exhibited an excellent recyclability, where no significant loss of the catalytic activity was showed out after 3 runs.
- Shu, Riyang,Zhang, Qi,Xu, Ying,Long, Jinxing,Ma, Longlong,Wang, Tiejun,Chen, Pengru,Wu, Qingyun
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p. 5214 - 5222
(2016/02/05)
-
- Preparation of silicalite-1@Pt/alumina core-shell catalyst for shape-selective hydrogenation of xylene isomers
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A silicalite-1@Pt/alumina core-shell catalyst that combined molecular sieving and hydrogenation was synthesized by coating silicalite-1 onto the surface of Pt/alumina pellet. While a Pt/alumina catalyst had no selectivity in the hydrogenation of xylene isomers, the silicalite-1@Pt/alumina core-shell catalyst showed much higher efficiency for the hydrogenation of p-xylene than for that of m- and o-xylene. The shape-selective hydrogenation catalyst has great potential for application in xylene separation.
- Wu, Yilan,Chai, Yongming,Li, Jiangchuan,Guo, Hailing,Wen, Ling,Liu, Chenguang
-
p. 110 - 113
(2015/03/04)
-
- Improving mass-transfer in controlled pore glasses as supports for the platinum-catalyzed aromatics hydrogenation
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The liquid-phase hydrogenation of toluene and other alkyl substituted benzene derivatives with different critical diameters was investigated over Pt-catalysts supported on spherical controlled pore glasses (CPGs) as model supports at 373 K in the batch mode. The effect of mass-transfer within the catalyst pores was studied by varying the pore width (4, 10, and 80 nm) and average grain size (18-150 μm) of the Pt/CPG catalysts. For toluene hydrogenation, internal mass-transfer limitations were absent (effectiveness factor >90%) only for catalysts with particle sizes below 25 μm and pore widths ≤10 nm or with a pore width of 80 nm and particle sizes around 75 μm, respectively. Effective diffusion coefficients obtained from initial reaction rates via the Thiele concept, e.g., 2.8 × 10-10 m2 s-1 for toluene over the catalyst with 10 nm pore width, were an order of magnitude lower than when determined by PFG-NMR. This difference was explained in terms of transport resistances such as surface barriers affecting the diffusivity assessment via the Thiele concept, while PFG-NMR measures intraparticle diffusion only.
- Goepel,Kabir,Küster,Sara?i,Zeigermann,Valiullin,Chmelik,Enke,K?rger,Gl?ser
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p. 3137 - 3146
(2015/06/08)
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- Production of alkanes from lignin-derived phenolic compounds over in situ formed Ni catalyst with solid acid
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In situ formed Ni catalyst combined with added solid acids is highly active for the hydrodeoxygenation of lignin-derived phenolic compounds. In the heterogeneous catalysts, in situ formed Ni acts as the hydrogenation and hydrogenolysis catalyst and solid acid acts as the dehydration catalyst.
- Zhang, Xinghua,Wang, Tiejun,Zhang, Qi,Xu, Ying,Long, Jinxing,Chen, Lungang,Wang, Chenguang,Ma, Longlong
-
supporting information
p. 648 - 650
(2015/05/20)
-
- Ruthenium nanoparticles supported on magnesium oxide: A versatile and recyclable dual-site catalyst for hydrogenation of mono- and poly-cyclic arenes, N-heteroaromatics, and S-heteroaromatics
-
The development of catalysts capable of promoting hydrogenation of aromatics while being resistant to poisoning by nitrogen- and sulfur-containing species is of much interest in connection with hydrotreating of fossil fuels. We report a catalyst composed of ruthenium nanoparticles supported on magnesia, designed to promote heterolytic hydrogen splitting and surface ionic hydrogenation pathways. The catalyst, prepared through a one-pot procedure, promotes the hydrogenation of mono- and poly-cyclic arenes, as well as N- and S-heteroaromatics representative of fossil fuels components. Of particular significance are the superior activity and wider substrate scope of the catalyst, in relation to other known supported noble metals, and the excellent recyclability and long catalyst lifetime. Based on our experimental data, a dual-site catalyst structure and an associated dual-pathway mechanism are proposed, which may have interesting implications for the development of new poison-tolerant noble metal catalytic systems.
- Fang, Minfeng,Sanchez-Delgado, Roberto A.
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p. 357 - 368
(2014/02/14)
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- Catalytic hydrogenation of aromatic rings catalyzed by Pd/NiO
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A simple and efficient heterogeneous palladium catalyst was prepared for aromatic ring hydrogenation. The catalyst was prepared by a reduction-deposition method and exhibited high activity and selectivity for the hydrogenation of a variety of substituted aromatic compounds to the corresponding cyclohexane and cyclohexanol derivatives with up to 99% yields. The catalyst was characterized by BET, TEM, XRD, XPS and ICP. Meanwhile the reusability of the catalyst was investigated, and it can be reused for several runs without significant deactivation.
- Wang, Yanan,Cui, Xinjiang,Deng, Youquan,Shi, Feng
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p. 2729 - 2732
(2014/01/06)
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- An efficient cleavage of the aryl ether C-O bond in supercritical carbon dioxide-water
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A simple and highly efficient Rh/C catalyzed route for the cleavage of the C-O bond of aromatic ether at 80 °C in the presence of 0.5 MPa of H 2 in the scCO2-water medium is reported; CO2 pressure and water play a key role under the tested conditions.
- Chatterjee, Maya,Ishizaka, Takayuki,Suzuki, Akira,Kawanami, Hajime
-
supporting information
p. 4567 - 4569
(2013/06/04)
-
- Rhodium nanoparticles stabilized with phosphine functionalized imidazolium ionic liquids as recyclable arene hydrogenation catalysts
-
Rhodium nanoparticles (Rh NPs) stabilized by phosphine functionalized ionic liquids (FILs) were prepared in [BDMI]NTf2 (BDMI = 1-butyl-2,3-dimethylimidazolium, NTf2 = bis(trifluoromethanesulfonyl) imide) using H2(g) (4 bar) as a reducer. Rh(allyl)3 was used as a "salt-free" Rh NP precursor and allowed to enhance the stability of the Rh NPs compared to the usual RhCl3 precursor. The synthesized FIL stabilized Rh NPs proved to be active biphasic catalysts for the hydrogenation of toluene, styrene and xylenes under mild conditions (75°C, 40 bar H2(g), 3 h). The impact on activity of the length of the spacer between the phosphine function and the ionic liquid moiety in the FIL was studied. The Rh NPs stabilized by FILs showed higher catalytic activity and recyclability than NPs synthesized in the absence of a stabilizer and more stable than the system employing triphenylphosphine (PPh3) as a stabilizer. The size of the stabilized Rh NPs was measured to be around 2 nm by TEM, while those produced in the absence of a FIL stabilizer formed only aggregates.
- Stratton, Samantha A.,Luska, Kylie L.,Moores, Audrey
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experimental part
p. 96 - 100
(2012/06/18)
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- Enhanced rate of arene hydrogenation with imidazolium functionalized bipyridine stabilized rhodium nanoparticle catalysts
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The imidazolium functionalized bipyridine compounds, {4,4'-bis-[7-(2,3- dimethylimidazolium)heptyl]-2,2'-bipyridine}2+ ([BIHB]2+) and {4,4'-bis[(1,2-dimethylimidazolium)methyl]-2,2'-bipyridine}2+ ([BIMB]2+), were prepared and used as Rh nanoparticle stabilizers. The dispersed Rh nanoparticles were used as catalysts in the biphasic hydrogenation of various arene substrates. The catalytic activity was strongly influenced by the stabilizer employed and followed the trend [BIHB] > bipy > [BIMB]2+. The steric and electronic characteristics of the imidazolium functionalized bipyridine ligands were assessed via the synthesis of rhenium carbonyl complexes, which facilitated the rationalization of the catalytic properties of the nanoparticles.
- Dykeman, Ryan R.,Yan, Ning,Scopelliti, Rosario,Dyson, Paul J.
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scheme or table
p. 717 - 719
(2011/04/23)
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- Hydrogenation of arenes and N-heteroaromatic compounds over ruthenium nanoparticles on poly(4-vinylpyridine): A versatile catalyst operating by a substrate-dependent dual site mechanism
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A nanostructured catalyst composed of Ru nanoparticles immobilized on poly(4-vinylpyridine) (PVPy) has been synthesized by NaBH4 reduction of RuCl3·3H2O in the presence of the polymer in methanol at room temperature. TEM measurements show well-dispersed Ru nanoparticles with an average diameter of 3.1 nm. Both powder XRD patterns and XPS data indicate that the Ru particles are predominantly in the zerovalent state. The new catalyst is efficient for the hydrogenation of a wide variety of aromatic hydrocarbons and N-heteroaromatic compounds representative of components of petroleum-derived fuels. The experimental data indicate the existence of two distinct active sites in the nanostructure that lead to two parallel hydrogenation pathways, one for simple aromatics involving conventional homolytic hydrogen splitting on Ru and a second one for N-heteroaromatics taking place via a novel heterolytic hydrogen activation on the catalyst surface, assisted by the basic pyridine groups of the support.
- Fang, Minfeng,MacHalaba, Nataliya,Sanchez-Delgado, Roberto A.
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experimental part
p. 10621 - 10632
(2011/11/29)
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- Ruthenium(0) nanoclusters supported on hydroxyapatite: Highly active, reusable and green catalyst in the hydrogenation of aromatics under mild conditions with an unprecedented catalytic lifetime
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The preparation of ruthenium(0) nanoclusters supported on hydroxyapatite and their characterization by a combination of complementary techniques are described. The resultant ruthenium(0) nanoclusters provide high activity and reusability in the complete hydrogenation of aromatics under mild conditions (at 25 °C and with 42 psi initial H2 pressure).
- Zahmakiran, Mehmet,Tonbul, Yalcin,Oezkar, Saim
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supporting information; experimental part
p. 4788 - 4790
(2010/09/10)
-
- Ionic-liquid-like copolymer stabilized nanocatalysts in ionic liquids: II. Rhodium-catalyzed hydrogenation of arenes
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Rhodium nanoparticles stabilized by the ionic-liquid-like copolymer poly[(N-vinyl-2-pyrrolidone)-co-(1-vinyl-3-butylimidazolium chloride)] were used to catalyze the hydrogenation of benzene and other arenes in ILs. The nanoparticle catalysts can endure forcing conditions (75 °C, 40 bar H2), resulting in high reaction rates and high conversions compared with other nanoparticles that operate in ILs. The hydrogenation of benzene attained record total turnovers of 20,000, and the products were easily separated without being contaminated by the catalysts. Other substrates, including alkyl-substituted arenes, phenol, 4-n-propylphenol, 4-methoxylphenol, and phenyl-methanol, were studied and in most cases were found to afford partially hydrogenated products in addition to cyclohexanes. In-depth investigations on reaction optimization, including characterization of copolymers, transmission electron microscopy, and an infrared spectroscopic study of nanocatalysts, were also undertaken.
- Zhao, Chen,Wang, Han-zhi,Yan, Ning,Xiao, Chao-xian,Mu, Xin-dong,Dyson, Paul J.,Kou, Yuan
-
-
- Alumina-, niobia-, and niobia/alumina-supported NiMoS catalysts: Surface properties and activities in the hydrodesulfurization of thiophene and hydrodenitrogenation of 2,6-dimethylaniline
-
The activity of NiMoS catalysts supported on niobia, alumina, and niobia/alumina was compared for the thiophene hydrodesulfurization (HDS) and 2,6-dimethylaniline (2,6-DMA) hydrodenitrogenation (HDN) reactions. To evaluate the acidity of the supports and identify the nature of the sulfide sites, adsorption of 2,6-dimethylpyridine, pyridine, and CO was performed and followed by IR spectroscopy. This study has shown that with niobia as a support, the activity of NiMoS catalysts in thiophene HDS and in HDN of 2,6-DMA was no longer promoted by the synergy between Ni and Mo. The absence of synergy between molybdenum and nickel on niobia can be explained by the strong interaction of each metal with niobia at the expense of interaction with each other. Moreover, it has been shown that on a niobia/alumina support, the formation of the NiMoS phase can be directly linked to the presence of alumina not covered by niobia. However, niobia is an interesting support for the HDN of 2,6-DMA, because it favors the formation of xylene through direct ammonia elimination involving low H2 consumption. The activity for xylene formation on niobia is linked to the electron-deficient nature of the Mo sulfide site, as demonstrated by CO adsorption followed by IR.
- Rocha, Angela S.,Faro Jr., Arnaldo C.,Oliviero, Laetitia,Van Gestel, Jacob,Mauge, Francoise
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p. 321 - 334
(2008/09/18)
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- A simple and reproducible method for the synthesis of silica-supported rhodium nanoparticles and their investigation in the hydrogenation of aromatic compounds
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Colloidal suspensions of rhodium nanoparticles have been easily prepared in aqueous solution by chemical reduction of the precursor RhCl 3·3H2O in the presence of the surfactant N,N-dimethyl-N-cetyl-N-(2-hydroxyethyl)ammonium chloride (HEA16Cl) and further used to immobilize rhodium nanoparticles on silica by simple impregnation. The obtained silica-supported rhodium nanoparticles have been investigated by adapted characterization methods such as transmission electron microscopy and X-ray photoelectron spectroscopy. A particle size increase from 2.4 to 5 nm after the silica immobilization step and total elimination of the surfactant has been observed. This "heterogeneous" catalyst displayed good activities for the hydrogenation of mono-, di- alkylsubstituted and/or functionalized aromatic derivatives in water under atmospheric hydrogen pressure and at room temperature. In all cases, the catalyst could be recovered several times after a simple decantation or filtration and reused without any significant loss in catalytic activity. This supported catalyst has also been tested under higher hydrogen pressure giving rise to TOFs reaching 6430 h -1 at 30 bar and in terms of catalytic lifetime 30 000 TTO in 8.5 h for pure anisole hydrogenation at 40 bar. the Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2006.
- Mevellec, Vincent,Nowicki, Audrey,Roucoux, Alain,Dujardin, Christophe,Granger, Pascal,Payen, Edmond,Philippot, Karine
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p. 1214 - 1219
(2007/10/03)
-
- Supramolecular cluster catalysis: Facts and problems
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By checking the chemistry underlying the concept of "supramolecular cluster catalysis" we identified two major errors in our publications related to this topic, which are essentially due to contamination problems. (1) The conversion of the "closed" cluster cation [H3Ru3(C6H6) (C6Me6)2(O)]+ (1) into the "open" cluster cation [H2Ru3 (C6H6)(C6Me6)2 (O)(OH)]+ (2), which we had ascribed to a reaction with water in the presence of ethylbenzene is simply an oxidation reaction which occurs in the presence of air. (2) The higher catalytic activity observed with ethylbenzene, which we had erroneously attributed to the "open" cluster cation [H2Ru3 (C6H6)(C6Me6)2 (O)(OH)]+ (2), was due to the formation of RuO2·nH2O, caused by a hydroperoxide contamination present in ethylbenzene.
- Süss-Fink, Georg,Therrien, Bruno,Vieille-Petit, Ludovic,Tschan, Mathieu,Romakh, Vladimir B.,Ward, Thomas R.,Dadras, Massoud,Laurenczy, Gabor
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p. 1362 - 1369
(2007/10/03)
-
- Stereochemistry of hydrodenitrogenation: The mechanism of elimination of the amino group from cyclohexylamines over sulfided Ni-Mo/γ-Al2O3 catalysts
-
HDS and HDN are among the most significant catalytic processes in the petroleum industry, because during these processes sulfur and nitrogen are removed in the form of H2S and ammonia from oil fractions. The HDN of cyclohexylamine and of the diastereomers of 2-methylcyclohexylamine and 2,6-dimethylcyclohexylamine was studied at 200°-350°C and 50 bar over a sulfided Ni-Mo/γ-Al2O3 catalyst. The rate of HDN of alkyl-substituted cyclohexylamines over sulfided Ni-Mo catalysts depended on the number of β hydrogen atoms and on their stereochemical relation to the amino group. Isomerization of olefinic products and the amines prevented meaningful mechanistic studies at 350°C. The cis diastereomers reacted faster than the trans diastereomers, because they allowed for an anti geometric relationship in the chair conformation between the amino group and a hydrogen atom on a β carbon atom. The syn elimination occurred to a considerable extent at higher temperatures in molecules that were unable to undergo anti elimination. The activation energy of anti elimination was lower than that of syn elimination, and the activation energy of anti elimination involving a hydrogen atom attached to a tertiary β carbon atom was lower than that involving a hydrogen atom attached to secondary β carbon atom.
- Prins,Ranade,Rota,Ranade
-
p. 389 - 399
(2007/10/03)
-
- Cyclization of methyl-substituted 6-heptenyl radicals
-
(Matrix presented) The behavior of a series of methyl-substituted 6-heptenyl radicals, generated from the corresponding iodides ((Me3Si)3SiH, AIBN in benzene at 80°C), has been investigated. The stereoselectivity of the 6-exo cyclizations, affording dimethylcyclohexanes, is low, and sizable quantities of methylcycloheptane, generated via 7-endo cyclization, are also produced.
- Bailey, William F.,Longstaff, Sarah C.
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p. 2217 - 2219
(2007/10/03)
-
- Direct aromatic C-N bond cleavage evidenced in the hydrodenitrogenation of 2,6-dimethylaniline over cobalt-promoted Mo/Al2O3 sulfide catalysts: A reactivity and FT-IR study
-
The hydrodenitrogenation of 2,6-dimethylaniline (DMA) was studied over a series of sulfided Co(0-4.7%)-Mo(8.7%)/Al2O3 catalysts at 573 K under 4 MPa total pressure and 0-56 kPa H2S partial pressure. Two NiMo samples were tested for comparison. The reaction network presents three parallel routes: dearomatization of DMA followed by either hydrogenation-elimination to dimethylcyclohexenes and dimethylcyclohexanes, or NH3 elimination to mxylene, and disproportionation of DMA to 2-methylaniline and 2,4,6-trimethylaniline. We demonstrate that part of the xylene is formed by direct aromatic carbon-nitrogen bond cleavage through a nucleophilic substitution involving hydride species. On CoMo catalysts, in the presence of H2S, the amount of extra xylene is independent of Co content, while the dearomatization is promoted. Without H2S, this special substitution reaction is most important on the Mo catalyst, and strikingly Co acts as a poison. FT-IR spectroscopy of adsorbed carbon monoxide evidences a new type of sites on the sulfided catalysts after a mild hydrogen treatment. We propose that a site configuration located exclusively on unpromoted Mo atoms highly depleted in sulfur is responsible for the direct denitrogenation route. The NiMo couple behaves differently: xylene formation is independent of Ni content, which means that the specific Mo sites for direct C-N bond rupture are poisoned by nickel, even in the presence of H2S. The location of Co and Ni on the MoS2 slabs then appears different.
- Van Gestel,Dujardin,Mauge,Duchet
-
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- EFFECTIVE GAS-PHASE DEOXYGENATION OF ALCOHOLS AND KETONES ON IRON CATALYST
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A method of gas-phase deoxygenation of alcohols and ketones into hydrocarbons on iron catalyst at 600 K and 1-2E5 Pa is dicussed.
- Glebov, L. S.,Mikaya, A. I.,Yatsenko, A. E.,Zaikin, V. G.,Kliger, G. A.,Loktev, S. M.
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p. 3373 - 3376
(2007/10/02)
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- High temperature catalytic hydrogenolysis and alkylation of anisole and phenol
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Hydrogenation of phenol at 2.8 MPa pressure with MoO3-NiO-Al2O3 catalyst at 450 deg C gave 60 percent benzene, 16 percent cyclohexane, and 7 percent methylcyclopentane, while anisole under the same conditions gave 60-70 percent less of each these products and 52 percent methylated benzenes.In the presence of added methanol either phenol or anisole give 47-63 percent of methylbenzenes and 22 percent of methylated phenols.At 350-400 deg C significant yields of cyclohexylbenzene and cyclohexylphenol were formed.The reactions are interpreted as involving electrophilic methylation or cyclohexylation of phenol concurrent with ring hydrogenation and hydrogenolysis of C-O bonds.Cyclohexyl cations are proposed as reactive intermediates that act as cyclohexylating agents or rearrange to methylcyclopentyl cations, and the methylating species is derived from methanol or the methyl group of anisole.When phenol was reacted with H2 and CD3OH the methylated aromatic products were only partially deuterated, indicating exchange with the H2 atmosphere was occurring.Control experiments involving possible intermediates in the reaction are consistent with these conclusions.Nickel catalysts favour ring saturation over C-O bond cleavage.
- Kallury, R. K. M. R.,Tidwell, T. T.,Boocock, D. G. B.,Chow, D. H. L.
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p. 2540 - 2545
(2007/10/02)
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- Biphasic hydrogenation of olefins, dienes, and α,β-unsaturated carbonyl compounds catalyzed by the dimer of chloro(1,5-hexadiene)rhodium
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Olefins, dienes, and trienes can be hydrogenated in an aqueous-organic two-phase medium using the dimer of chloro(1,5-hexadiene)rhodium as the catalyst.Selective reduction of the double bond of α,β-unsaturated carbonyls occurs in high yields.These reactions occur at room temperatures and atmospheric pressure, and are simple to work up.
- Januszkiewicz, Krzysztof R.,Alper, Howard
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p. 1031 - 1033
(2007/10/02)
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- VERSATILE POLYMER-BOUND RHODIUM CATALYSTS. FACILE HYDROGENATION OF AROMATIC COMPOUNDS IN THE LIQUID PHASE
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Immobilized complexes prepared from 2 (nbd=norbornadiene) and phosphinated polydiacetylene or silica are efficient catalysts for the hydrogenation of arenes under mild conditions.However, the homologous catalyst supported on a phosphinated polystyrene is not active.
- Okano, Tamon,Tsukiyama, Katsunori,Konishi, Hisatoshi,Kiji, Jitsuo
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p. 603 - 606
(2007/10/02)
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- Catalytic Hydrogenation of Aromatic Hydrocarbons. Stereochemical Definition of the Catalytic Cycle for η3-C3H5Co(P(OCH3)3)3
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The η3-C3H5Co(P(OCH3)3)3-catalyzed hydrogenations with D2of a series of unsaturated organic molecules, including cyclohexenes, cyclohexadienes, and arenes, have been investigated.Complete cis stereoselectivity was observed in the addition of deuterium to the unsaturated ring systems.When alkyl-substituted arenes were reduced with D2, the hydrogen atoms in the alkyl chains underwent H-D exchange as long as each successive carbon atom in the chain possessed at least one hydrogen atom.Hence, extensive H-D exchange occured in n-alkyl side chains while the tert-butyl side chain was deuterium free.When alkyl-substituted arenes were hydrogenated in the presence of olefins such as 1-hexene, a variety of isomeric alkylcyclohexenes and alkenylcyclohexanes were observed.The relative concentrations of these isomeric species provided information about the relative stabilities of the (olefin)cobalt species in the catalytic cycle.Further mechanistic information was obtained from other competitive reactions, i.e., hydrogenation reactions involving equimolar quantities of two different unsaturated molecules.The proposed initiation steps of the catalytic cycle have been revised on the basis of a study of η3-C8H13Co(P(OCH3)3)3 as a catalyst precursor.The cyclooctenyl-cobalt bond was cleaved by hydrogen early in the reaction, leaving the highly coordinately unsaturated hydride, HCo(P(OCH3)3)2, which is probably the true catalytic species.
- Bleeke, J. R.,Muetterties, E. L.
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p. 556 - 564
(2007/10/02)
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