Liquid-phase Hydrogenation Of Cyclohexene Research Articles

Unraveling Toluene Conversion during the Liquid Phase Hydrogenation of Cyclohexene (in Toluene) with Rh Hybrid Catalysts

Monitoring hydrogen consumption has allowed studying the progress of the liquid phase hydrogenation of cyclohexene in toluene with Rh SILP (supported ionic liquid phase) catalysts prepared by the immobilization of the [{RhCl(cod)}2] complex on different carbon materials. An excess of hydrogen consumption with respect to the required amount for cyclohexene hydrogenation was registered and related with the solvent (toluene) hydrogenation. The study carried out led to unraveling the extent of toluene hydrogenation and to determining if the rate of this reaction is affected by the properties of the carbon material used as support. The results revealed that the Rh SILP catalysts we prepared showed acceptable toluene conversion, with 100% selectivity to the total hydrogenated product, and that the effect of the carbon support is the same as for cyclohexene hydrogenation.

Organic polymers as solid hydrogen donors in the hydrogenation of cyclohexene

Liquid hydrogen donors have found limited industrial application due to the difficulty of their separation from the reaction product. To solve this problem a novel type of solid hydrogen donor is developed and applied in the liquid-phase hydrogenation of cyclohexene on a Pt/Al2O3 catalyst. A significant increase in the reaction rate is observed when using the solid hydrogen donor, particularly in the initial stage of the reaction, when the reaction rate is zero order with respect to cyclohexene. The selectivity to cyclohexane was also improved.

Kinetics of liquid phase cyclohexene hydrogenation on Pd–Al/biomorphic carbon catalysts

The biomorphic mineralization technique is a powerful tool that allows to synthetize inorganic materials using as templates some structures of biological origin. This work presents kinetics results obtained during the liquid-phase hydrogenation of cyclohexene using a novel Pd–Al catalyst supported on biomorphic carbon.The catalysts have been prepared by a reactive method, using cellulose as carbonaceous precursor of the biomorphic support. The influence of the time and decomposition temperature (600–800°C) of cellulose under hydrogen atmosphere has been studied. The characterization results indicate that the synthesis of these biomorphic materials produce solids with high microporosity. The metallic dispersion of the Pd nanoparticles is strongly dependent on the preparation conditions (i.e. heating rate, thermal decomposition temperature and time) of the carbonaceous precursor.The kinetic study has covered the effect of the hydrogen pressure and temperature, and was carried out using a real-time in situ Raman probe. The developed kinetic model considers the non-competitive adsorption between hydrogen and cyclohexene in two different types of Pd metallic sites. The model explains all the experimental results obtained, providing a rational explanation for the variation of the kinetic orders and apparent activation energy obtained using the empirical power-law model.

Preparation of highly active heterogeneous Au@Pd bimetallic catalyst using plant tannin grafted collagen fiber as the matrix

Au@Pd bimetallic nanoparticles (NPs) catalysts were synthesized by a seeding growth method using bayberry tannin grafted collagen fiber (BT-CF) as the matrix. In this method, Au3+ was first reductively adsorbed onto BT-CF to form Au NPs, and then they serve as the seeds for the over growth of Pd shell. The morphology of BT-CF-Au@Pd catalyst was observed by TEM and SEM, and the core–shell structure of the Au@Pd was confirmed by EDS and XRD. It was found that the as-prepared BT-CF-Au9@Pd3 catalyst showed excellent synergy effect in liquid-phase hydrogenation of cyclohexene, whose reaction time was three times faster than that catalyzed by BT-CF-Pd catalyst under the same conditions. Meanwhile, the BT-CF-Au9@Pd3 catalyst could be re-used four times without significant loss of activity. In the fourth run, the substrate conversion was still as high as 92.70%, much better than that by using commercial Pd/C catalyst (42.60%). Additionally, BT-CF-Au9@Pd3 catalyst exhibited high hydrogenation activity to various alkenes and nitro-compounds. For example, the TOF of allyl alcohol, styrene and nitrobenzene hydrogenations reached 10,980, 14,732 and 1379molmol−1h−1, respectively.

A comparative study of liquid-phase hydrogenation on Pd/SiO 2 in organic solvents and under pressurized carbon dioxide: Activity change and metal leaching/sintering

Liquid-phase hydrogenation of cyclohexene under mild conditions on Pd/SiO 2 in different organic solvents (benzene, heptanol, and NMP), under pressurized carbon dioxide, and under solvent less condition were investigated and compared. In the cases of using organic solvents, the hydrogenation rates depended on polarity of the solvents in which the reaction rates in high polar solvents such as heptanol and NMP were lower than that in a non-polar solvent. Hydrogenation rates were much higher when the reactions were performed under high-pressure CO 2 or under solvent less condition. The use of high-pressure CO 2 can probably enhance H 2 solubility in the substrate resulting in a higher hydrogenation activity. However, metal sintering and leaching in the presence of high-pressure CO 2 were comparable to those in organic solvents.

Preparation and Activity of Small Rhodium Metal Particles on Fishbone Carbon Nanofibres

A number of different impregnation and ion-exchange procedures have been employed to synthesize very small rhodium metal particles on HNO3/H2SO4-oxidized fishbone carbon nanofibres. The surface-oxidation of the nanofibres with HNO3/H2SO4 is a prerequisite for a good interaction between aqueous catalyst precursor solutions and the fibres. Depending upon the preparation technique applied and using 1 wt% rhodium metal loadings average particle sizes ranging from 1.1 to 2.1 nm were detected with XAFS spectroscopy. The rhodium metal particles are so small that metal–support interactions on carbon nanofibres can be investigated with XAFS spectroscopy. All catalysts are highly active in the liquid-phase hydrogenation of cyclohexene. No significant effect of particle size on the catalytic activity is observed, suggesting that other factors, such as clustering of the support particles in the liquid phase, are much more important.

Preparation and Activity of Small Rhodium Metal Particles on Fishbone Carbon Nanofibres

A number of different impregnation and ion-exchange procedures have been employed to synthesize very small rhodium metal particles on HNO 3/H 2SO 4-oxidized fishbone carbon nanofibres. The surface-oxidation of the nanofibres with HNO 3/H 2SO 4 is a prerequisite for a good interaction between aqueous catalyst precursor solutions and the fibres. Depending upon the preparation technique applied and using 1 wt% rhodium metal loadings average particle sizes ranging from 1.1 to 2.1 nm were detected with XAFS spectroscopy. The rhodium metal particles are so small that metal–support interactions on carbon nanofibres can be investigated with XAFS spectroscopy. All catalysts are highly active in the liquid-phase hydrogenation of cyclohexene. No significant effect of particle size on the catalytic activity is observed, suggesting that other factors, such as clustering of the support particles in the liquid phase, are much more important.

Modification of carbon nanofibres for the immobilization of metal complexes: a case study with rhodium and anthranilic acid.

The immobilisation of the rhodium/anthranilic acid complex onto fishbone carbon nanofibres (CNFs) was executed by means of the following steps: 1) surface oxidation of the fibres, 2) conversion of the oxygen-containing surface groups into acid chloride groups, 3) attachment of anthranilic acid and 4) complexation of rhodium by the attached anthranilic acid. The immobilisation process was followed and the resulting surface species were characterised by IR, X-ray absorption fine structure (XAFS) and X-ray photoelectron spectroscopy (XPS), and by molecular modelling. Anthranilic acid bonds to the CNFs by an amide linkage to the carboxyl groups that are present after surface oxidation of the fibres. The immobilised anthranilic acid coordinates to rhodium through the nitrogen atom and the carboxyl group. The assynthesised RhIII complex itself is not active in the liquid-phase hydrogenation of cyclohexene. Reduction with sodium borohydride yields small particles (d = 1.5-2 nm) of rhodium metal that are highly active. The results indicate that different activation procedures for the immobilised Rh/anthranilic acid system should be applied, such as reduction with a milder reducing agent or direct complexation of the rhodium in the RhI state.

Properties of Pt/C and Pd/C catalysts prepared by reduction with hydrogen of adsorbed metal chlorides: Influence of pore structure of the support

A number of catalysts have been prepared by adsorption of H 2PdCl 4 and H 2PtCl 6 on activated carbons of different origin followed by drying and reduction in flowing hydrogen. They were characterised by CO chemisorption and by liquid-phase hydrogenation of cyclohexene, cyclooctene and nitrobenzene. A decisive influence of the pore structure of the support on the catalyst properties has been found. By a proper choice of the preparation conditions, it proved possible to obtain a sufficiently high dispersion of the supported metal on any one of the activated carbons used. However, catalytic activity per mass of metal reached a maximum in the range of intermediate metal dispersion, with the limit being dependent on the support used. This is attributed to deposition of metal particles of high dispersion in narrow pores of the supports, which renders part of the metal surface inaccessible to the organic substrates. Such a blocking effect proved especially significant for Pt catalysts on the activated carbons with the smallest micropores.

Ruthenium-C 60 compounds: properties and catalytic potential

Ruthenium-C 60 compounds were prepared by reaction of Ru 3(CO) 12 with C 60 in refluxing toluene. The resulting compounds were found to be insoluble air-stable solids which consist of an amorphous matrix embedding small ruthenium metal particles of an average size of 2–5 nm. Furthermore, the presence of unreacted C 60, small amounts of toluene and a residual CO-ligand sphere in ruthenium-C 60 was found. The catalytic activity of ruthenium-C 60 compounds at different temperatures was shown in prototype reactions like the liquid-phase hydrogenation of cyclohexene at 300 K or the hydrogenation of CO in the Fischer-Tropsch synthesis at 500 K.

Liquid-Phase Hydrogenation of Cyclohexene over Pt Foil Catalysts

A liquid-phase reaction cell, coupled to an ultrahigh-vacuum surface analysis chamber, was built to study liquid-phase hydrogenation reactions on small area model catalyst surfaces. The hydrogenation of cyclohexene to cyclohexane was studied at about 1.5 atm total pressure of H2and as a function of temperature in the 313–333 K range in liquid cyclohexene. The hydrogenation rate of cyclohexene on a clean Pt surface increased with the increasing circulation velocity of the liquid, indicating that the reaction rate was controlled by hydrogen diffusion to the surface. When the surface reaction rate was reduced by the deposition of hydrocarbon fragments on the platinum surface, the rate of cyclohexene hydrogenation became independent of hydrogen diffusion and became controlled by the kinetics of the surface reaction. The estimated activation energy of the reaction is 6 kcal/mol for cyclohexene hydrogenation on a platinum foil that was partly covered with carbonaceous deposits.

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.

Liquid-phase hydrogenation of cyclohexene by dihydrogen in the presence of dimolybdenum tetraacetate

Catalytic liquid-phase hydrogenation of cyclohexene in DMF by dihydrogen in the presence of dinuclear bridged complex Mo2(OAc)4 has been studied. A kinetic equation for the steady-state rate of cyclohexene hydrogenation and the activation parameters are suggested.

Pd/SiO2–AlPO4 systems. Influence of the preparation variables on their catalytic activity

A study on the liquid phase hydrogenation of cyclohexene over a series of Pd catalysts supported on various SiO2–AlPO4 systems (using a concentration of 2.47 M, with methanol as solvent, the initial hydrogen pressure is 5 bar and reaction temperature 300 K) is reported in this paper. The reaction has been studied as a standard in order to determine the most suitable preparation conditions for these catalystsWe have also studied the influence of other factors such as the kind of support, the nature of the metal precursor, the previous calcination of the precursor, the addition of alkaline hydroxides, and the catalyst reduction with various agents, on the catalytic activity of different Pd-supported systems

Catalytic hydrogenation of cyclohexene: Part II. Liquid phase reaction on supported platinum in a gradientless slurry reactor

AbstractThe areal rate of liquid phase hydrogenation of cyclohexene on supported platinum catalysts does not depend on the nature of the support. Nor does it depend on particle size of the metal. The rate constant is independent of the nature of the solvent when the concentration of hydrogen in it is expressed as its measured or calculated solubility. All observations are compatible with the idea that the measured rate is that of chemisorption of dihydrogen on a metal surface covered with reactive hydrocarbon intermediates.

Study of the catalytic and adsorption properties of ruthenium catalysts in the hydrogenation of cyclohexene

1. Ruthenium blacks are comparatively active catalysts of the liquid-phase hydrogenation of cyclohexene. 2. In the presence of catalysts containing ruthenium oxide, the hydrogenation of cyclohexene proceeds with an induction period, which is accompanied by a sharp shift of the potential in the anodic direction, to 400 mV. 3. Charging curves of ruthenium black were obtained. A measurement of the surface according to the double-layer capacitance of ruthenium black is impossible, since together with charging of the surface there is an adsorption of oxygen. More reliable values are obtained when the surface is determined according to the hydrogen region. 4. The bond energies of the surface ruthenium atoms to hydrogen and to carbon at the double bond in the cyclohexene molecule were calculated, and it was demonstrated that the presence of oxides in the catalyst decreases the bond energy of the catalyst to hydrogen and increase the bond energy to carbon.

Liquid-phase hydrogenation and irreversible catalysis of cyclohexene on a skeletal nickel catalyst

1. In the presence of a skeletal nickel catalyst, the rate of hydrogenation of cyclohexene in dilute alcohol solutions depends on the concentration. At concentrations of 0.5–5.0 millimoles/ml, the reaction proceeds at a constant rate. In the absence of a solvent, the reaction does not proceed. 2. Liquid-phase hydrogenation of cyclohexene on skeletal nickel at 20–60° is accompanied by a reaction of irreversible catalysis. Redistribution of hydrogen also occurs when the cyclohexene is in contact with the catalyst in an atmosphere of nitrogen. 3. The benzene and cyclohexane formed in the process of conversion of cyclohexene lower the reaction rate of the hydrogenation of cyclohexene.