Hydrogenation Of Cyclohexene Research Articles

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.

Heptamolybdate-intercalated CoMgAl hydrotalcites as precursors for HDS-selective hydrotreating catalysts

Two series of unsupported CoMgMoAl hydrotreating catalysts were prepared starting from CoMgAl-terephthalate layered double hydroxides (LDHs) with nominal aluminum molar fractions (Al/(Al+Ni+Mg) ratios) 0.3 (Al30 series) and 0.5 (Al50 series), and nominal cobalt atom fractions (Co/(Co+Mg)) in the 0.2–1.0 range in each series. The materials were prepared by ion exchange with ammonium heptamolybdate, followed by calcination at 723K. Mixed oxides containing ca. 14–32wt.% molybdenum and Ni/Mo atomic ratios in the 0.5–1.6 range were obtained. Despite the observed loss in long-range ordering and, in some cases, magnesium leaching during the ion-exchange, there was evidence that molybdenum-intercalated LHDs were indeed produced.The catalysts were sulfided in situ and subsequently tested in simultaneous thiophene HDS and cyclohexene hydrogenation (OHYD reaction) in a tubular flow micro-reactor at 573 and 623K and 20bar. In each series, both the HDS and the OHYD activities of the catalysts increased with increasing Mg content, possibly due to improved Co/Mo ratio. Although there was a trend of decreasing selectivity for the HDS reaction with increasing HDS activity, the HDS selectivity of the most active catalysts was higher than that of a commercial alumina-supported CoMo catalyst.

Pd nanoparticles immobilized in a microporous/mesoporous composite ZIF-8/MSS: A multifunctional catalyst for the hydrogenation of alkenes

The work reports a new hierarchically core–shell structure that consists of a catalytically active core made of palladium–decorated mesoporous silica spheres (Pd/MSS) and an outer shell of microporous ZIF-8. The synthesis process involves (i) the preparation of MSS via supramolecular templating using a modified Stöber method, (ii) the loading of palladium nanoparticles into MSS, followed by (iii) the surface modification of Pd/MSS catalyst with polyelectrolyte to promote the nucleation and growth of a ZIF-8 shell. The core–shell Pd/MSS@ZIF-8 was characterized by X-ray diffraction, electron microscopy (SEM & TEM), FTIR, ICP-AES and N2 physisorption to determine its physicochemical properties. The core–shell Pd/MSS@ZIF-8 was used to catalyze the hydrogenation of 1-hexene and cyclohexene. Results showed that the Pd/MSS@ZIF-8 was a multifunctional catalyst with excellent reactant shape-selectivity, leaching-proof ability, improved poison resistance and good recyclability in contrast to the conventional Pd/MSS catalyst.

Organometallic Preparation of Ni, Pd, and NiPd Nanoparticles for the Design of Supported Nanocatalysts

The preparation of bimetallic nanoparticles with controlled size, shape, and composition remains a difficult task, and reproducible methods are highly desired. Here, we report the codecomposition of Ni(cod)2 and Pd2(dba)3 organometallic precursors in the presence of hexadecylamine (HDA) and hydrogen as an efficient approach to get size-controlled bimetallic nickel–palladium nanoparticles. Presynthesized nickel–palladium nanoparticles of different Ni/Pd ratios were further used for the preparation of supported catalysts by the sol–immobilization method onto a magnetic silica. The obtained supported catalysts were investigated in the hydrogenation of cyclohexene and compared to Ni and Pd monometallic catalysts. The catalysts prepared with a 1:9 Ni/Pd molar ratio achieved the highest initial turnover frequency > 50 000 h–1, providing higher activity than the pure Pd monometallic counterpart. This represents an important saving of noble metal. Moreover, the magnetic separation allows excellent separation of t...

Crystal Structure Characterization and Catalytic Application of Novel Route Prepared Ru3(CO)9 DPAM (Diphenyl Arsino Methane)-tri Phenyl Phosphine Derivatives

Triruthenium dodecacarbonyl-Ru3(CO)12 based diphenylarsino methane-triphenyl phosphine derivatives, such as Ru3(CO)9-dpam-tris (methyl phenyl) phosphine (1), Ru3(CO)9-dpam-tris (methoxy phenyl) phosphine (2), and Ru3(CO)9-dpam-tris (fluro phenyl) phosphine (3) are synthesized by two step modified method. The catalytic hydrogenation of cyclohexene, styrene, and phenyl acetylene, on above mentioned Ru-based organometallic catalysts, has been studied under high pressure hydrogen atmosphere. The high pressure hydrogenation of cyclohexene and phenyl acetylene on Complex (1–3), showed good catalytic activity under pressurized condition. Hydrogenation of cyclohexene on Complex (3) showed better (50–65%) conversion in the presence of toluene than hexane solvent. The effect of temperature, role of solvent, and pressure conditions have also been studied.

The synthesis of multiphasic ionic liquid-coated Pt/Al2O3catalysts: the selective synchronous hydrogenation of CC and CO bonds and the modeling of the ionic liquid and solvent effects

Various ionic liquids (ILs) and their mixtures were coated on the Pt/Al2O3 catalyst and the resulting IL-coated catalysts were used in the synchronous hydrogenation of cyclohexene and acetone. The rate constant (k) and selectivity (S) toward CO hydrogenation were determined for several catalysts in various solvents. The solvatochromic parameters (ETN, normalized polarity parameter; π*, dipolarity–polarizability; β, hydrogen-bond acceptor basicity; α, hydrogen-bond donor acidity) were determined for the used ILs and solvents and the obtained selectivities were modeled based on the solvatochromic parameters of the IL layer and bulk solvent while using the Multiparameter Linear Regression (MLR) method for the first time. Selectivity toward the CO bond increases by increasing the percentage of 2-hydroxy ethylammonium formate (HEAF) in the IL layer and decreasing the polarity of the solvents. The single-parameter correlations of lnS versus π* presented the best correlation for the prepared catalysts in all solvents.

Hydrogenation by nanoscale ruthenium embedded into the nanopores of K-10 clay

Ruthenium(0) nanoparticles in the size range 1–4 nm were generated in the nanopores of the fine fraction of Montmorillonite K-10 clay by in situ glycol reduction of RuCl3·3H2O impregnated clay. The synthesized catalyst was characterized by Powder XRD, SEM, TEM, DRS and BET surface area determination. TEM/HRTEM/SAED images revealed the growth of well dispersed Ru(0) nanoparticles having lattice fringes with interplanar spacing 0.21 nm corresponding to the [101] plane of hexagonal close packed ruthenium. The catalytic activity of the synthesized catalyst was tested for hydrogenation of cyclohexene to cyclohexane. The clay embedded Ru nanoparticles act as an efficient and recyclable environmentally friendly catalyst in hydrogenation of dextrose and phenol in aqueous medium under mild reaction conditions. Turn over frequency (TOF) of the catalyst was also calculated considering true active sites calculated on the basis of surface statistics and a model for full shell clusters.

Metal Nanoparticles/Ionic Liquid/Cellulose: Polymeric Membrane for Hydrogenation Reactions

Rhodium and platinum nanoparticles were supported in polymeric membranes with 10, 20 and 40 µm thickness. The polymeric membranes were prepared combining cellulose acetate and the ionic liquid (IL) 1-n-butyl-3-methylimidazolium bis(trifluoromethane sulfonyl)imide (BMI.(NTf)2. The presence of metal nanoparticles induced an increase in the polymeric membrane surface areas. The increase of the IL content resulted in an improvement of elasticity and decrease in tenacity and toughness, whereas the stress at break was not affected. The presence of IL probably causes an increase in the separation between the cellulose molecules that result in a higher flexibility and processability of the polymeric membrane. The CA/IL/M(0) combinations exhibit an excellent synergistic effect that enhances the activity and durability of the catalyst for the hydrogenation of cyclohexene. The CA/IL/M(0) polymeric membrane displays higher catalytic activity (up to 7.353 h-1) for the 20 mm of CA/IL/Pt(0) and stability than the nanoparticles dispersed only in the IL.

Impact of solvent for individual steps of phenol hydrodeoxygenation with Pd/C and HZSM-5 as catalysts

Impacts of water, methanol, and hexadecane solvents on the individual steps of phenol hydrodeoxygenation are investigated over Pd/C and HZSM-5 catalyst components at 473K in presence of H2. Hydrodeoxygenation of phenol to cyclohexane includes four individual steps of phenol hydrogenation to cyclohexanone on Pd/C, cyclohexanone hydrogenation to cyclohexanol on Pd/C, cyclohexanol dehydration to cyclohexene on HZSM-5, and cyclohexene hydrogenation to cyclohexane on Pd/C. Individual phenol and cyclohexanone hydrogenation rates are much lower in methanol and hexadecane than in water, while rates of cyclohexanol dehydration and cyclohexene hydrogenation are similar in three solvents. The slow rate in methanol is due to the strong solvation of reactants and the adsorption of methanol on Pd, as well as to the reaction between methanol and the cyclohexanone intermediate. The low solubility of phenol and strong interaction of hexadecane with Pd lead to the slow rate in hexadecane. The apparent activation energies for hydrogenation follow the order Ea phenol>Ea cyclohexanone>Ea cyclohexene, and the sequences of individual reaction rates are reverse in three solvents. The dehydration rates 1.1–1.8×103molmolBAS-1h-1 and apparent activation energies (115–124kJmol−1) are comparable in three solvents. In situ liquid-phase IR spectroscopy shows the rates consistent with kinetics derived from chromatographic evidence in the aqueous phase and verifies that hydrogenation of phenol and cyclohexanone follows reaction orders of 1.0 and 0.55 over Pd/C, respectively. Conversion of cyclohexanol with HZSM-5 shows first-order dependence in approaching the dehydration–hydration equilibrium in the aqueous phase.

Core–shell Pd/ZSM-5@ZIF-8 membrane micro-reactors with size selectivity properties for alkene hydrogenation

A well-designed Pd/ZSM-5@ZIF-8 core–shell structure has been prepared by application of a combination of seed-induction synthesis strategy and self-assembly synthesis techniques. First, uniform ZSM-5 particles with micron size and high crystallinity were prepared from organic-template-free gel systems containing 200nm ZSM-5 seeds and exchanged with Pd(NO3)2 aqueous solution. Then incompatibility between the Pd/ZSM-5 core material and ZIF-8 shell precursor was circumvented by surface modification using a layer by layer self-assembly of polyelectrolyte, followed by a subsequent two-step temperature synthesis process inducing the formation of continuous and well-intergrown ZIF-8 shell. Thickness of ZIF-8 shell can be simply tuned by monitoring the assembly cycles. Furthermore, hydrogenations of 1-hexene and cyclohexene were chosen as model reactions to evaluate the catalytic behavior of the Pd/ZSM-5@ZIF-8 core–shell architecture and tert-dodecylthiol was used as a poison to test its anti-poisoning ability. Results show that such core–shell architecture exhibits excellent poison resistance and selectivity control properties for the hydrogenation reactions and can be potentially used as a membrane reactor in the field of heterogeneous catalysis.

Effects of Pd on Catalysis by Au: CO Adsorption, CO Oxidation, and Cyclohexene Hydrogenation by Supported Au and Pd–Au Catalysts

Incorporating small amounts of Pd into supported Au catalysts has been shown to have beneficial effects on selective hydrogenation reactions, particularly 1,3-butadiene hydrogenation and the hydrogenation of nitroaromatics, especially p-chloronitrobenzene. Appropriate Pd incorporation enhances hydrogenation activity while maintaining the desirable high selectivity of supported Au catalysts. To better understand this phenomenon, a series of alumina- and titania-supported Au and dilute Pd–Au catalysts were prepared via urea deposition–precipitation. The catalysts were studied with infrared spectroscopy of CO adsorption, CO oxidation catalysis, and cyclohexene hydrogenation catalysis with the goal of understanding how Pd affects the catalytic properties of Au. CO adsorption experiments indicated a substantial amount of surface Pd when the catalyst was under CO. Adsorption experiments at various CO pressures were used to determine CO coverage; application of the Temkin adsorbate interaction model allowed for the determination of adsorption enthalpy metrics for CO adsorption on Au. These experiments showed that Pd induces an electronic effect on Au, affecting both the nascent adsorption enthalpy (ΔH0) and the change in enthalpy with increasing coverage. This electronic modification had little effect on CO oxidation catalysis. Michaelis–Menten kinetics parameters showed essentially the same oxygen reactivity on all the catalysts; the primary differences were in the number of active sites. The bimetallic catalysts were poor cyclohexene hydrogenation catalysts, indicating that there is relatively little exposed Pd when the catalyst is under hydrogen. The results, which are discussed in the context of the literature, indicate that a combination of surface composition and Pd-induced electronic effects on Au appear to increase hydrogen chemisorption and hydrogenation activity while largely maintaining the selectivities associated with catalysis by Au.

In situ preparation of Pd/Al2O3–SiO2 composite microspheres by combining a sol–gel process and precipitation process in a microchannel

Pd/Al2O3–SiO2 composite microspheres with 4nm Pd nanoparticles were prepared in a microchannel by combining a sol–gel process with the precipitation of Pd ion. The sol of silica and alumina with Pd ion was used as the dispersed phase, and liquid paraffin-containing soluble organic amines were used as the continuous phase. The mass transfer of organic amines from the organic phase to the aqueous phase in microchannels changed the pH of the aqueous phase, which resulted in the precipitation of PdCl2 in acidic solution and the faster sol–gel process of SiO2–Al2O3. The resulting catalyst was characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and Brunauer–Emmett–Teller analyses. Experimental results showed that the prepared microspheres with a diameter about 400μm had a special structure that was externally compact and internally, and they were suitable for packing into a fixed bed. Each microsphere had a microporous–mesoporous–macroporous structure and the specific surface area was larger than 600m2/g. After calcination at 550°C, the smallest Pd particles still had an average size of 3.79nm and were highly dispersed. These microspheres in a fixed bed also showed a high performance for the hydrogenation of cyclohexene. When the retention time was 2.2min in the liquid phase, a conversion rate reached 0.447. This one-step in situ synthesis had the advantages of high utilization of Pd, small Pd nanoparticles with high monodispersity, and adjustability of resulting microspheres at the micron level.

Promotion of Hydrogenation of Organic Molecules by Incorporating Iron into Platinum Nanoparticle Catalysts: Displacement of Inactive Reaction Intermediates

We characterize the surface chemical states of reactants and catalysts under reaction conditions to elucidate the composition effect of platinum–iron bimetallic nanoparticles on catalytic hydrogenation of organic molecules. The catalytic hydrogenation of ethylene is drastically accelerated on the surface of 2 nm PtFe bimetallic nanoparticles as compared to pure Pt. Sum frequency generation (SFG) vibrational spectroscopy indicates that incorporation of Fe into Pt nanoparticle catalysts weakens the adsorption of ethylidyne, an inactive spectator species, on the catalyst surface. Similarly, the turnover frequency of cyclohexene hydrogenation is also significantly enhanced by incorporating Fe into Pt nanoparticle catalysts. Ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) reveals the surface composition and oxidation states of the PtFe nanoparticles under reaction conditions. The oxidation state distribution of Fe responded to the gas atmosphere and the probing depth, whereas the Pt remained largely metallic in all probing conditions. This work represents a molecular level correlation between catalyst structure and catalytic performance.

Screening of Soluble Rhodium Nanoparticles as Precursor for Highly Active Hydrogenation Catalysts: The Effect of the Stabilizing Agents

We report the preparation of rhodium nanoparticles (NPs) stabilized by 1-octadecanethiol (ODT), polyvinyl alcohol (PVA), and tetraoctylammonium bromide (TOAB), and their application for hydrogenation catalysis. The three metal–ligand systems correspond to different mechanism of NPs stabilization via strong covalent linkage, chemisorbed atoms and electrostatic interactions, respectively. We found a strong effect of the interaction between the stabilizer and the surface of the metal nanoparticle on the catalytic activity. The Rh NPs were studied as soluble nanoparticle catalysts and as precursors for the synthesis of supported catalysts. All catalysts were tested in the hydrogenation of cyclohexene under similar conditions as a model reaction. Generally, Rh–ODT NPs were inactive, Rh–PVA NPs exhibited distinct activities in solution (aqueous biphasic catalysis) and as a supported catalyst, and Rh–TOAB NPs exhibited similar activities in solution and after immobilization. This last result opens the opportunity for the preparation of highly active Rh NP catalysts both in solution and as a heterogeneous catalyst. Additionally, the stability of the nanoparticles depends on the choice of ligand and on the functionalization of the support surface before immobilization. By optimizing the catalyst synthesis and reaction conditions, turnover frequencies as high as 700,000 h−1 where observed for stable and recyclable catalyst.

Ruthenium Carbene–Diether Ligand Complexes: Catalysts for Hydrogenation of Olefins

A series of carbene–diether ligands were prepared and the corresponding Ag salts used to prepare the complexes RuHCl(PPh3)2(Im(OR)2) (Im(OR)2 = C3H2(NCH2CH2OR)2; R = Me (4a), t-Bu (4b), tert-hexyl (4c), Ph (4d), 2,6-i-Pr2C6H3 (4e)). In an analogous fashion the species RuHCl(PPh3)2(Y2Im(OMe)2) (Y2Im(OMe)2 = Y2C3(NCH2CH2OMe)2; Y2 = C6H4 (4f), Y = Cl (4g), Me (4h)) were also synthesized. Similarly RuHCl(CO)(PPh3)2(Im(OMe)2) (5) was prepared and readily converted to RuHCl(CO)(SIMes)(Im(OMe)2) (6) via treatment with SIMes. The reaction of 4a with SIMes afforded RuHCl(SIMes)(Im(OMe)2)(PPh3) (7), which reacts subsequently with Na[BPh4] to give [RuH(Im(OMe)2)(SIMes)][(η6-Ph)BPh3] (8). In a series of tests, the species 4a–h, 5, 6, and 8 were shown to catalyze the hydrogenations of 1-hexene, cyclohexene, and dimethyl itaconate. From the activity of 4a–h it is clear that the capability of the carbene–ether substituents to coordinate to the metal as well as electron-donating substituents on the carbene fragment enhan...

Mesocellular silica foam supported Ni2P catalysts with high hydrogenation activity

A series of nickel phosphide (Ni2P) catalysts supported on Y zeolite, SBA-15 and mesocellular silica foams (MCF) were prepared by the thermal treatment of nickel chloride and sodium hypophosphite at low temperature. The catalysts were characterized by XRD, nitrogen adsorption–desorption and TEM, and evaluated in the hydrogenation of cyclohexene. The supported Ni2P catalysts exhibited an obvious difference in catalytic performances. Ni2P/MCF was demonstrated to be highly efficient among three kinds of catalysts because the ultra-large mesopores and large pore volume of MCF promote the dispersion of Ni2P and accelerate the diffusion of reactant and product. Under the reaction conditions of 80 °C and 1.5 MPa, 40 % Ni2P/MCF afforded a very high cyclohexene conversion of 97.5 %.

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.

Stabilizing unstable species through single-site isolation: a catalytically active TaV trialkyl in a porous organic polymer

A catechol-functionalized porous organic polymer (POP) has been successfully metallated with a TaV trialkyl and remains thermally and structurally robust. The resulting POP-supported (catecholato)TaV trialkyl sites remain accessible to small molecules and can undergo reactions to yield stable, monomeric complexes that are quite different from those observed with the homogeneous analogues. Using a combination of reactivity studies, high-resolution solid-state NMR spectroscopy, and X-ray absorption spectroscopy (XAS), we are able to precisely determine the functionality and coordination environment of the active (catecholato)TaV trialkyl site and its products in reactions with Bronsted acids. Additionally, the Ta-metallated POP was found to have enhanced catalytic activity in the hydrogenation of cyclohexene and toluene relative to a homogeneous analogue.

Rhodium complex immobilized on graphene oxide as an efficient and recyclable catalyst for hydrogenation of cyclohexene

Rhodium complexes can be homogeneously immobilized on functionalized graphene oxide through coordination interaction. The obtained catalyst can be readily recycled and shows enhanced activity in the catalytic hydrogenation of cyclohexene.

Taking advantage of a terpyridine ligand for the deposition of Pd nanoparticles onto a magnetic material for selective hydrogenation reactions

A hybrid terpyridine ligand was designed to functionalize a magnetic support constituted of magnetite cores surrounded by a silica shell with the aim of improving the stabilization of supported-palladium nanoparticles for the later application of the obtained composite nanomaterial in hydrogenation catalysis. The preparation of the nanomaterial was performed by direct decomposition of the organometallic complex [Pd2(dba)3] on the terpyridine-modified magnetic support providing well-dispersed Pd NPs of 2.5 ± 0.6 nm mean size. This new nanomaterial is a highly active catalyst for the hydrogenation of cyclohexene under mild conditions reaching turnover frequencies up to ca. 58 000 h−1 or 129 000 h−1 when corrected for surface Pd atoms. Furthermore, in the hydrogenation of β-myrcene, this nanocatalyst is highly selective for the formation of monohydrogenated compounds. When compared to a similar nanocatalyst consisting of palladium nanoparticles supported on an amino-modified magnetic support or on Pd/C, the activity and selectivity of the nanocatalyst are largely increased. These results show how the design of an appropriate hybrid ligand used to functionalize the support can strongly influence the catalytic properties of supported metal nanoparticles.