Hydrogenation Reactions Of Cyclohexene Research Articles

Hydrogenation of Cyclohexene in Aqueous Solvent Mixture Over a Sustainable Recyclable Catalyst Comprising Palladium and Monolacunary Silicotungstate Anchored to MCM‐41

An efficient, highly stable, and ligand‐free catalyst consisting of Pd and monolacunary silicotungstate anchored to MCM‐41 was synthesized and characterized by various techniques. The synthesized catalyst was used for the hydrogenation reaction of cyclohexene as model substrate, and various reaction parameters were studied in order to optimize them for maximum conversion, 95 %, under mild conditions. The catalyst was regenerated by simply washing with methanol and reused up to three cycles without significant loss in activity. The viability of the catalyst was evaluated for different alkenes and ketones, and in all cases the conversion was found to be in the range of 92–99 %. It was also found that the sustainability arises from SiW11, which binds the palladium very strongly and thus does not allow its leaching into the reaction mixture.

A study of palladium hydrogenation catalysts based on nanodiamonds and activated carbon

Palladium hydrogenation catalysts based on nanodiamonds and activated carbon with a metal content of 1 wt % have been studied by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). It has been shown that the nature of the support has an effect on the electron binding energy of palladium and the stability of metal sites formed during supporting. The resulting catalysts exhibit activity in the model nitrobenzene and cyclohexene hydrogenation reactions under mild conditions (T = 318 K; $${P_{{H_2}}}$$ = 0.1 MPa; solvent, ethanol); the nanodiamond-based catalyst is significantly more active and efficient than the counterpart based on activated carbon.

Effect of microwave heating on the synthesis of rhodium nanoparticles in ionic liquids

A comparative study of the synthesis of Rh nanoparticles (RhNPs) in ionic liquid media (1-butyl-3-methylimidazoliumbis(trifluoromethylsulfonyl)imide) by conventional and microwave heating is presented. Controlled injection of hydrated RhCl3 precursor into mixtures of the ionic liquid and poly(N-vinylpyrrolidone) under convective electrical heating yielded near-monodisperse (6.9±1.1nm) RhNPs with a mixture of morphologies. In contrast, identical reactions performed under microwave-assisted heating showed greater morphological selectivity, resulting in largely homogeneous samples of cubic and truncated cubic RhNPs (5.7±0.9nm). Interestingly, X-ray photoelectron spectroscopic analysis of the microwave-synthesized RhNPs revealed a greater surface population of BMIM-NTf2 when compared to the conventionally prepared RhNPs. This is indicative of a larger degree of incorporation of ionic liquid monomers coordinated to the RhNP surfaces and may be responsible for the enhanced shape selectivity. The catalytic ability of the as-synthesized nanoparticles was probed through vapor-phase cyclohexene hydrogenation reactions, yielding average TOF values of 9.2 for supported RhNPs.

Palladium (0) metal clusters: Novel Krebs type polyoxoanions stabilized, extremely active hydrogenation catalyst

One-pot synthetic route has been applied for successful synthesis and stabilization of Pd, Au and Ag metal-clusters (Metal-clusters can be defined as nanoparticles of size less than 10nm.) using Krebs type polyoxoanions [(TBA)4H4[M4(H2O)10(XW9O33)2], where M=Mn, Ni, Zn, X=Te, Se; M=Fe, X=Sb, As] as stabilizers. These polyoxoanions falls under the category of heteropolyanions and possess Krebs structure. All the polyoxoanion-metal colloidal systems were found to be stable for approximately three/six months in solution media. It was found that, due to some kind of structural transformation, polyoxoanions loose their stabilizing capability.Polyoxoanions stabilized Pd metal-clusters was found to be extremely active toward hydrogenation reaction of cyclohexene and 1-hexene. The Pd-Mn4Se2W18 system demonstrated the longest lifetime of up to 250,000 for 1-hexene and 100,000 for cyclohexene hydrogenation. The catalytic activity is found to vary with transition metal ions like Mn, Fe, Ni, Zn, As, Sb, Te, Se which are present in the polyoxoanions. All the metal-cluster systems were characterized using various instrumental techniques such as UV–vis spectroscopy, FTIR spectroscopy, X-ray diffraction, energy dispersive spectroscopy, X-ray photoelectron spectroscopy and transmission electron microscopy.

Characterization of Pt catalysts supported by three forms of TiO2 and their catalytic activities for hydrogenation

Three forms of TiO2, commercial TiO2 powder, hydrogen titanate nanotubes obtained by hydrothermal treatment, and the thermally stable TiO2 nanotubes prepared by treating hydrogen titanate nanotubes with a sol containing titanium, were used as supports, and Pt nanoparticles were deposited on the supports via the photodeposition method. The catalytic performances of as-prepared and calcined Pt/TiO2 catalysts for the hydrogenation reaction of cyclohexene were evaluated. The results showed that the effects of the support and calcination temperature on the catalytic performances of Pt/TiO2 catalysts were obvious and significant. The thermally stable nanotubular TiO2-supported Pt catalyst exhibited better catalytic performance than the other TiO2-supported Pt catalysts. In addition, it was discovered that the calcination can enhance the catalytic activity of Pt/TiO2 for hydrogenation greatly.

Hybrid polymer-immobilized palladium nanoparticles: Preparation and catalytic properties

A new approach to the synthesis of mixed-type immobilized catalysts was developed: the frontal polymerization of a metal-containing monomer in the presence of a highly dispersed mineral support. The synthesis of an acrylamide complex of Pd(II) nitrate on the surface of SiO2, Al2O3, or C and its subsequent polymerization and reduction resulted in the formation of an organic-inorganic composite that included nanosized Pd particles stabilized by a polymer matrix and an inorganic support. The resulting hybrid nanocomposites are efficient and selective catalysts for the hydrogenation reactions of cyclohexene and alkene and acetylene alcohols.

Polymerization and Catalytic Properties of Cluster‐Containing Monomers and Polymers

AbstractSummary: Cluster‐containing monomers were obtained and characterized. Mono‐ and disubstituted products were obtained under mild conditions via the interaction of Rh6(CO)16 with 4‐vinylpyridine (4‐VPy). Substitution of labile acetonitrile ligand in Rh6(CO)15NCMe by allyldiphenylphosphine (AlPPh2) yields Rh6(CO)14(µ,η2‐PPh2CH2CHCH2) with formation of π‐complex. The copolymerization of cluster‐containing monomers synthesized with traditional monomers has been studied. It was found that Rh6‐ containing monomers change neither the ligand surroundings nor the structure of cluster monomer framework during polymerization reaction. Polymer‐immobilized clusters were found to be active in hydrogenation reactions of cyclohexene.

Nanoclustered palladium(0) supported on a gel-type poly-acrylonitrile– N, N-dimethylacrylamide–ethylenedimethacrylate resin: Nanostructural aspects and catalytic behaviour

Gel-type resin poly-acrylonitrile (30 mol%)– N, N-dimethylacrylamide (66 mol%)–ethylenedimethacrylate (4 mol%) (ADE) is obtained in very high yield with γ-rays-sustained polymerisation in mass. Water-swollen ADE microparticles react readily with [PdCl 4 2−] in water to give a macromolecular complex likely to be ▪. The material undergoes facile reduction to a Pd 0/ADE nanocomposite, in which a surprisingly non-homogeneous distribution of Pd 0 nanoclusters suggests a remarkable inhomogeneity in the distribution of the –CN groups through the polymer framework. This circumstance is attributed to a marked occurrence of a block-type polymerisation of the acrylonitrile leading to spheroidal domains that are particularly rich in –CN functionalities. Pd 0/ADE appears to be an active, re-usable, mechanically and chemically stable catalyst in the model hydrogenation reaction of cyclohexene in methanol under moderate conditions, carried out in batch reactors.

Rhodium(I) Complexes with OPPy2Ph and OPPy3 (Py = 2-Pyridyl), and Their Behavior in Hydrogenation Reactions

The reaction of [Rh2(µ-Cl)2(COD)2] (COD = 1,5-cyclooctadiene) or [Rh2(µ-Cl)2(TFB)2] (TFB = tetrafluorobenzobicyclo[2.2.2]octatriene) with the N-donor chelating ligand OPPy2Ph (Py = 2-pyridyl) in the presence of TlBF4 affords cationic complexes [Rh(diene)(OPPy2Ph)](BF4) (1, diene: COD; 2, diene: TFB). Compounds 1 or 2 react with CO to give [Rh(CO)2(OPPy2Ph)](BF4) (4), which is also obtained by treatment of [Rh2(µ-Cl)2(CO)4] with OPPy2Ph and TlBF4. In a similar way, the complexes [Rh(diene)(OPPy3)](BF4) (5, diene: COD; 6, diene: TFB) are obtained when using OPPy3; they react with CO to give [Rh2(µ-CO)3(OPPy3)2](BF4)2 (9). The behavior of the complexes in solution is reported. The complexes with OPPy3, 5 and 6, show equivalence of the three Py groups in their NMR spectra. Complex 5 is square-planar in the solid state, and in solution, and the uncoordinated and coordinated Py groups undergo fast exchange in solution. Complex 6 is pentacoordinated in the solid state and in solution, and its Py groups exchange their coordination sites in a fast topomerization process. The single-crystal X-ray structures of 5 and 6 have been solved. The behavior of 1 and 5 as catalysts in hydrogenation reactions of cyclohexene, acetone, and cyclohexanone is also reported.

Olefin hydrogenation with iron carbonyls as catalysts

The use of [Fe(CO)5] , [Fe2(CO)9] and [Fe3(CO)12] as catalytic precursors in the hydrogenation reactions of cyclohexene and 1-hexene was investigated. A photochemical reactor with H2 flux and UV-vis continuous irradiation was used for these studies. The infrared spectra of the samples showed the formation of [Fe(CO)4(olefin)] and [HFe(CO)3(p-allyl)] as intermediates. The activity of [Fe2(CO)9] in the hydrogenation of cyclohexene was higher (66.6%) than the activity of the other iron carbonyls (43.0% [Fe(CO)5], [Fe3(CO)12]). The competition between isomerization and hydrogenation in the reaction of 1-hexene was studied. The isomerization rate was much higher than the hydrogenation rate and the polynuclear species provided faster isomerizations than [Fe(CO)5]. The alkane conversions were: 60.0% ([Fe(CO)5], [Fe3(CO)12]) and 75.4% ([Fe2(CO)9]), showing that for the 1-hexene hydrogenation [Fe2(CO)9] also exhibited the highest activity.

Homogeneous hydrogenation reaction with two tridentate rhodium(I) chelate complexes of various ring size

Each kinetically examined catalyst of the type LRhCl (L = bis(3-(diphenylphosphino)propyl)amine, PPA, and bis(4-(diphenylphosphino-butyl)benzyl)amine, PBA) was prepared through a reaction between the tridentate ligands and [Rh(COD)Cl] 2 in a polar solvent. The products obtained were both identified by means of elemental analysis, mass spectroscopic, 1H, 13C and 31P NMR and IR measurements. The geometry of the ligand donor atoms (2 × P, N and Cl) is square planar in these complexes, as is normally observed in Rh(I) coordination compounds. Via kinetic measurements of hydrogenation reactions of cyclohexene as substrate in the range of 20–50 °C and 800–1200 hPa H 2 pressure, it was found that the catalyst (PPA) RhCl has an activation energy E A of 52.3 kJ mol −1 and that of (PBA)RhCl is 45.3 kJ mol −1. The observed difference of 7.0 kJ mol −1 relates to a chelate ring size dependency, decreasing on going from a six- to a seven-membered chelate ring. The rate-determining step of the overall hydrogenation process with both catalysts probably is dependent on a chloride dissociation step. Consequently, on going from nonpolar to polar solvents for the examined hydrogenation processes under comparable reaction conditions, the observed hydrogenation rate (TON) of both catalysts increases. The substrate dependency of the two catalysts determined in a hydrogenation reaction is increased as follows: terminal olefins > cyclic olefins ≈ chelating olefins > cis -olefins > trans -olefins > multiply-substituted olefins; alkynes as substrates also achieved good initial hydrogenation rates.

Thermodynamics of homogeneous hydrogenation: Part VI. Thermodynamics of the homogeneous hydrogenation of cyclohexene catalyzed by Rh(I) and Ir(I) complexes of polydentate phosphine ligands

The oxidative addition of H 2 to the mixed ligand Rh(I) complex [RhCl(PPh 3)(diphos)] 1 and the Rh(I) and Ir(I) complexes of the terdentate ligands NP 3, [N(CH 2CH 2PPl 2) 3] and triphos, [PhP(CH 2CH 2PPh 2] 2 MLC1 2 – 5 (where M = Rh(I), Ir(I); L = NP 3, triphos) proceeds at 30 °C and 1 atm of Ha in ethanol-benzene with the formation of the thermodynamically stable cis dihydrides [RhCl(PPh 3)(diphos)(H) 2] 1a, 1b; [RhCl(NP 3)(H) 2] 2a, 2b; [RhCl(triphos)(H)2] 3a, 3b; [IrCl(NP3)(H)2] 4a and [IrCl(triphos)-(H) 2] 5a, 5b characterized by their hydride NMR in situ. The hydrides of iridium 4a, 4b, 5a, 5b are more stable in solution than their corresponding rhodium analogues. The homogeneous hydrogenation of cyclohexene catalyzed by complexes 1 – 5 was investigated in the temperature range 10 – 40 °C at 0.6 – 1 atm of h 2 partial pressure. Thermodynamic parameters for the formation of the dihydrido complexes of 1 – 5 and the monoolefin complexes of Rh(I) and Ir(I) were computed. The activation parameters corresponding to the rate constant k for the homogeneous hydrogenation of cyclohexene were also calculated. The enthalpy of formation Δ H o for the formation of hydrido and olefin complexes are more exothermic for the Ir(I) complexes compared to the Rh(I) complexes. The catalytic activity of the complexes decreases in the order 2 > 1 > 3 > 4 ≈ 5. The catalytic activity of the chelates 2 and 4 of the potential terdentate ligand NP 3 with a large chelate ring is much higher than complexes 3 and 5 of the rigid terdentate ligand triphos. The catalytic activity of the Rh(I) and Ir(I) complexes of triphos is more than those of the NP 2 [HN(CH 2CH 2PPh 2) 2] complexes. An inverse relationship exists between Δ H o, the enthalpy of formation of the hydrido complexes and Δ H ‡, the enthalpy of activation of the hydrogenation reaction of cyclohexene by a variety of polydentate complexes of Rh(I) and Ir(I) with P or N, P donors.

Iridium(I) complexes containing bidentate pyrazolylgallate ligands. X-ray crystal structures of [Me2Gapz2]Ir(COD), [Ir(μ-pz)(CO)2]2, and [Ir(μ-3,5-Me2pz)(CO)2]2

The synthesis and characterization of a number of Ir(I) complexes incorporating bidentate, chelating, pyrazolylgallate ligands are described. Non-rigidity for some of the complexes in solution has been demonstrated by variable temperature 1H nmr studies. Crystal structures of three complexes, [Me2Gapz2]Ir(COD), [Ir(μ-pz)(CO)2]2, and [Ir(μ-3,5-Me2pz)(CO)2]2 are reported and confirm the expected boat conformations for the six-membered M—(N—N)2—Ir rings (where M = Ir or Ga) in the compounds. One of the complexes studied has exhibited measurable activity as a catalyst in the hydrogenation reaction of cyclohexene.

Formation of pyrolytic carbon from benzene over nickel and some properties of the carbon formed

The rate of carbon formation during the catalytic decomposition of benzene vapor over nickel plates was investigated at temperatures from 600 to 970°C. The rate of carbon deposition on the pure nickel was very slow, whereas the rate became fast upon pretreatment of the nickel surface with air at 760°C. Nickel particles of 200–300 Å in diameter were included within the carbon. The nickel contents were 11, 4, 3, and 2 wt% for the carbons deposited at 700, 760, 800, and 900°C for 6 hr, respectively. Direct observations of the deposition process were performed in a scanning electron microscope. The formation of fibrous carbons was observed at the initial stage of the deposition at 760°C. The catalytic activity of this carbon including nickel particles was examined in the hydrogenation reaction of cyclohexene. A high catalytic activity was observed when the nickel-carbon catalyst was pretreated with hydrogen at a high temperature such as 600°C. This fact suggests that the nickel particles were surrounded by carbon, and the carbon was gasified to methane upon treatment with hydrogen at a high temperature.