Hydrogenation Of Cyclohexene Research Articles

Synthesis, characterization, and performance evaluation of unsupported tetrametallic CoMoMnAl and CoMoZnAl catalysts for selective hydrodesulfurization (HDS)

New formulations of unsupported tetrametallic catalysts derived from layered double hydroxides (LDH) compounds were synthesized by a constant pH coprecipitation method, characterized, and evaluated in the selective hydrodesulfurization (HDS) of thiophene in the presence of cyclohexene. The layered double hydroxides were prepared using terephthalate (C8H8O2)2- as the interlayer anion with nominal aluminum molar fraction of 0.5, and nominal cobalt to MII (M = Zn or Mn) ratios of 0.2, 0.4 and 0.6. Molybdenum introduction in the LDH precursor was accomplished by an ion exchange process using the heptamolybdate anion. The calcined Mn samples showed a higher surface area than those obtained from Zn. The sulfidation was carried out in situ with a heating ramp up to 673 K and the catalysts were evaluated in a tubular flow reactor. The catalytic evaluation of Zn and Mn-based materials for simultaneous thiophene HDS and cyclohexene hydrogenation (HYD) was conducted at 573 K and 20 bar. The results show that the Zn-based unsupported catalysts synthesized here exhibited higher selectivity for the HDS reaction than an industrial one.

Catalytic consequences of the identity and coverages of reactive intermediates during benzene hydrogenation on Pt, Pd, and Pt-Re catalysts

Mechanistic differences in benzene and cyclohexene hydrogenation on Pt, Pd, and Pt-Re catalysts are interrogated with kinetic assessments, temperature programmed surface reactions, infrared absorption spectroscopic study, and DFT calculations. Their effective rate constants are larger on Pt than Pd surfaces either uncovered or covered with sulfur species, due to the weaker H* adsorption and higher SH* acidity on Pt than Pd. Without sulfur species, H* is the only reactive hydrogen species—on Pt, its first insertion on the adsorbed benzene (C6H6*) and its second insertion onto the cyclohexene intermediate (C6H10+1*) restrict turnovers in benzene and cyclohexane hydrogenation, respectively. H2S treatments lead to SH* species bound irreversibly that not only decreases turnovers but also alters the elementary steps and their kinetic relevance within the catalytic cycle—SH* initially attacks C6H6*, before five successive H* additions, where the third addition limits turnovers. Incorporating isolated Re atoms onto sulfur-covered Pt surfaces increases benzene hydrogenation turnovers, because OH* associated with Re sites are more acidic and effective in initiating the reaction.

Electrochemical de-alloying synthesis of porous AuTiCeOx/NC cyclohexene hydrogenation SPE membrane electrode by combination method

Electrochemical de-alloying synthesis of porous AuTiCeOx/NC cyclohexene hydrogenation SPE membrane electrode by combination method

Synthesis of nanoporous solid polymer electrolyte AuNiCe/NC hydrogenation membrane electrode

In this study, using graphite fiber cloth as the support, gold-based solid polymer electrolyte (SPE) membrane electrodes were synthesized by high-vacuum ion beam sputtering, nitrogen doping of the support, combined electrochemical dealloying, and hot-pressing technology. The application of the SPE membrane electrode to couple hydrogen evolution and liquid organic hydrogen storage is of significant importance for sustainable hydrogen energy and efficient carbon dioxide conversion. Using various characterization techniques, we systematically analyzed the phase structure, surface morphology, porous structure, and electrocatalytic performance of the membrane electrode for the hydrogenation of cyclohexene. The results indicated that doping the carbonaceous support with nitrogen (NC), doping with cerium as catalyst promoter, and combined electrochemical dealloying can all enhance the activity of the catalyst. Cerium doping provides the catalyst with oxygen vacancies for accelerated electron transfer. After combined electrochemical dealloying, AuNiCe/NC formed a three-dimensional bicontinuous porous structure. The electrochemically active surface area increased by 23.94 times, the energy consumption of catalytic cyclohexene hydrogenation decreased by 35.7%, and current efficiency and the formation rate of cyclohexane increased by 54.9% and 29.4%, respectively.

Engineered Ru on HY zeolite catalyst for continuous and selective hydrodeoxygenation of lignin phenolics to cycloalkanes under moderate conditions

We report a continuous selective hydrodeoxygenation (HDO) process of guaiacol conversion to cycloalkanes under 180 °C/1 MPa, which results in improved HDO chemistry for lignin-based jet fuel production. The incipient wetness impregnation method was modified to prepare an HY zeolite-supported Ru catalyst with better metal dispersion and acid site uniformity, which overcomes the low conversion and selectivity of previous literature. The modified catalyst (Ru-HY-60-MI) was tested in a continuous fixed bed reactor, resulting in increased HDO conversion of guaiacol to cycloalkanes compared to the unmodified catalyst. Pressure, temperature, and weight hourly space velocity-dependent tests validate guaiacol HDO over Ru-HY-60-MI catalyzed ring hydrogenation of guaiacol to 2-methoxycyclohexanol, acid-catalyzed demethoxylation and dehydration to cyclohexene, and further hydrogenation of cyclohexene to cyclohexane. These experiments enable exploring a continuous HDO process, demonstrate effectiveness for other β-β and α-O-4 lignin representatives and real lignin bio-oil, and pave the way towards commercialization of lignin-based jet fuel.

Hydrogenation of cyclohexene over single-atom Pt or Pd incorporated porous ceria nanoparticles under solvent-free conditions.

In order to maximize the utilization of noble metals in catalysis, single atom of palladium (Pd) and platinum (Pt) were incorporated individually in the framework of porous ceria (CeO2) by using a one-step flash combustion method. Samples with different Pd and Pt loading (0.5, 1, 2.5, and 5 wt%) were prepared and examined by using different analysis techniques such as XRD, ICP, N2 sorption measurements, SEM, HR-TEM, and XPS. The characterization data confirms the formation of zero-state single-atom Pt and Pd (with possible formation of Pd nanoparticles with a size less than 5 nm) incorporated onto the three-dimensional porous ceria structure. The catalytic activity of the synthesized materials was studied in the cyclohexene reduction to cyclohexane at 393 K and 3 atm of pure hydrogen (H2) gas as a model reaction. The obtained results demonstrated that the conversion percentage of cyclohexene is increasing with Pd or Pt loading. The best cyclohexene conversion, 21% and 29%, was achieved over the sample that contains 5 wt% of Pt and Pd, respectively. The collected catalytic data fit the zero-order reaction model, and the rate constant of each catalyst was determined. The catalytic experiments of the most-performed catalysts were repeated five times and the obtained loss in activity was insignificant.

Highly Porous Para-Aramid Aerogel as a Heterogeneous Catalyst for Selective Hydrogenation of Unsaturated Organic Compounds.

A new para-aramid aerogel based on a polymer made by the reaction of terephthaloyl dichloride with 2-(4-aminophenyl)-1H-benzimidazol-5-amine (PABI) is introduced. The aerogel readily bound Pd (+2) ions and was used as a hydrogenation catalyst in some industrially actual reactions. The new material, which did not contain p-phenylenediamine moieties, was prepared in two form factors: bulk samples and spherical pellets of 700-900 μm in diameter. Aerogels were synthesized from 1% or 5% solutions of PABI in N,N-dimethylacetamide via gelation with acetone or isopropanol and had a density of 0.057 or 0.375 g/cm3 depending on the concentration of the starting PABI solution. The specific surface area of the obtained samples was 470 or 320 m2/g. Spherical pellets containing Pd were prepared from a solution of PdCl2 in PABI and were used as heterogeneous catalysts for the gas-phase hydrogenation of unsaturated organic compounds presenting the main types of industrially important substrates: olefins, acetylenes, aromatics, carbonyls, and nitriles. Catalytic hydrogenation of gaseous hexene-1, hexyne-3, cyclohexene, and acrylonitrile C=C bond proceeded with a 99% conversion at ambient pressure, but the catalyst failed to reduce acetone at 150 °C and benzene and ethyl acetate even at 200 °C. The only product of acrylonitrile hydrogenation was propionitrile. The prepared catalysts showed high selectivity, which is important for the chemistry of complex organic compounds.

Synthesis of reinforced porous Pt-based alloy SPE membrane electrodes for hydrogenation of cyclohexene by electrochemical etching

Synthesis of reinforced porous Pt-based alloy SPE membrane electrodes for hydrogenation of cyclohexene by electrochemical etching

Co-Promoted CoNi Bimetallic Nanocatalyst for the Highly Efficient Catalytic Hydrogenation of Olefins

Bimetallic catalysts, especially non-noble metals, hold great potential for substituting for noble metals in catalytic hydrogenation. In present study, a series of CoxNiy (x + y = 6) bimetallic catalysts were prepared through the impregnation–reduction method and cyclohexene was chosen as probe-molecule to study the promotion effect of Co on the catalytic olefin hydrogenation reactions. Meanwhile, density functional theory (DFT) was utilized to investigate the formation energies and the charge distribution of CoNi bimetals, as well as the transition state (TS) searches for hydrogen dissociation and migration. The results suggest that bimetals tend to have superior catalytic performance than pure metals, and Co3Ni3 shows the highest catalytic activity on the cyclohexene hydrogenation. It was found that the charge transfer from Co to Ni and the alloying give rise to the refinement of CoNi grains and the improvement of its catalytic activity and stability. Thus, it may be possible to obtain better catalytic performance by tuning the metal/metal atomic ratio of bimetals.

Green synthesis of Fe3O4@ZnO-supported Pd nanoparticles for oxidation and hydrogenation reactions in liquid systems

In this work Pd nanoparticles immobilized on a hybrid solid support comprised of Fe3O4 coated by a ZnO layer were synthesized by a green method which makes use of water, a biological substrate from a local plant (Rhamnidium elaeocarpum) and inexpensive Fe3+ and Zn2+ salts. 1H-NMR and 13C-NM revealed β-sitosterol as the main component of the biological substrate. The catalytic support containing Pd nanoparticles was applied in three model solid-liquid catalytic systems, namely: alcohol oxidation, nitrocompound reduction and olefin hydrogenation. For the alcohol oxidation, benzyl alcohol was used as the substrate in a solvent-free condition with high selectivity towards benzaldehyde, and a single sample of the catalyst could be recycled up to 11 times before any loss of activity could be detected. TOF (turnover frequency) as high as 13,686 h-1 for the substrate oxidation was achieved with an average yield rate of 45.4% for formation of benzaldehyde and 81.6% of average substrate conversion after 6 catalytic cycles. For the hydrogenation experiments using cyclohexene and 4-nitrophenol as model substrates, conversion as high as 96% to 4-aminophenol and cyclohexane, respectively, was achieved after 30 minutes of reaction. Furthermore, a single sample of the catalyst could be recycled for up to 17 times for the reduction of 4-nitrophenol, and 21 times in the hydrogenation of cyclohexene. Catalytic recycling for all studied reactions was straightforward after due to the superparamagnetic property of the material, and catalyst isolation after each batch could be rapidly carried out using a Nd magnet. These results suggests that a highly active and stable catalytic system based on Pd nanoparticles supported on a multifunctional solid could be fabricated using green and inexpensive biomass under operationally simple synthesis conditions.

Effect of Different Zeolite Supports on the Catalytic Behavior of Platinum Nanoparticles in Cyclohexene Hydrogenation Reaction

In this study, 1 wt% platinum (Pt) nanoparticles were incorporated into five types of zeolites (HY, Beta, mordenite, ZSM-5, and ferrierite) with an impregnation technique. The synthesis strategy included the use of water as a solvent for the applied Pt source. Moreover, the incorporation process was performed at ambient conditions followed by calcination at 450 °C. The five prepared materials were characterized by different physical and chemical characterization techniques and the obtained results confirmed the formation of Pt nanoparticles with an average size of 5–10 nm. The catalytic performance of the prepared materials was evaluated in the hydrogenation of cyclohexene under a solvent-free system at room temperature. Pt nanoparticles supported on ZSM-5 zeolite exhibited the best catalytic performance. Moreover, the optimization of operational conditions such as temperature, pressure, and catalyst amount was investigated and the obtained results showed the possibility to convert 100% of cyclohexene within 35 min over Pt-ZSM-5. Finally, the reusability of the Pt-ZSM-5 catalyst was investigated in four consecutive runs without treatment and the obtained results showed a negligible activity loss.

Preparation of Pd Nanoparticles Stabilized by Modified Montmorillonite for Efficient Hydrodeoxygenation of Lignin-Derived Phenolic Compounds in Water

Developing a new and efficient catalytic route for the production of alkanes by upgrading the aqueous phenolic biofuels still remains a challenge. Here, we designed and synthesized a bifunctional catalyst that uses natural montmorillonite (MMT) as support and combines metal active sites and Brӧnsted acid sites in the MMT via ion exchange and reduction roasting process. The catalytic activity of the as-synthesized Pd-MMT (H+) was evaluated by the hydrodeoxygenation (HDO) of a series of lignin-derived phenolic compounds in water. Our model reaction study reveals that the HDO of phenol undergoes an initial hydrogenation of aromatic rings to produce cyclohexanol and cyclohexanone, followed by the dehydration of cyclohexanol to provide intermediate cyclohexene and a final hydrogenation of cyclohexene to create a cyclohexane product. The combination of high metal catalytic activity and Brӧnsted acidity in Pd-MMT (H+) synergistically accelerated the HDO of phenol. Furthermore, good catalytic activity and recycling ability were also observed for other lignin-derived phenolic compounds.

Catalytic Reactions at Amine-Stabilized and Ligand-Free Platinum Nanoparticles Supported on Titania during Hydrogenation of Alkenes and Aldehydes.

Ligands like amines are used in the colloidal synthesis approach to protect platinum nanoparticles (Pt NP's) from agglomeration. Normally, ligands like amines are removed by diverse pre-treatment procedures before use in heterogeneous catalysis as amines are considered as a catalyst poison. However, a possible beneficial influence of these surface modifiers on hydrogenation reactions, which is known from spectator species on metal surfaces, is often neglected. Therefore, amine-stabilized Pt nanoparticles supported by titania (P25) were used without any pre-treatment in order to elucidate a possible influence of the ligand in liquid phase hydrogenation reactions. The catalytic activity of amine-stabilized Pt nanoparticles of two different sizes was investigated in a double-walled stirring tank reactor at 69 °C to 130 °C and 1 atm hydrogen pressure. The conversion of cyclohexene to cyclohexane was determined by gas chromatography (GC) and was compared to ligand-free Pt particles. All catalysts were checked before and after reaction by transmission electron spectroscopy (TEM) and X-ray photoelectron spectroscopy (XPS) for possible changes in size, shape, and ligand shell. The hydrogenation of cyclohexene in liquid phase revealed a higher conversion for amine-stabilized Pt nanoparticles on titania than the ligand-free particles. The hydrogenation of 5-methylfurfural (5-MF) was chosen for a further test reaction, since the hydrogenation of α, β-unsaturated aldehydes is more complex and exhibits various reaction paths. However, XPS and infrared spectroscopy (IR) proved that 5-MF acts as catalyst poison at the given reaction conditions.

Synthesis and characterization of naphthaldiimine-based ruthenium(III) complexes; homogenous catalytic hydrogenation and isomerization of internal and terminal alkenes

This study is concerned with synthesis and characterization of four naphthaldiimine ligands and their ruthenium(III) complexes. The tetradentate diimines were synthesized by a Schiff condensation reaction between 2-hydroxy-1-naphthaldehyde and various aliphatic diamines with chains of 2, 4, 5 and 6 carbon atoms. Analytical, mass spectra, thermal and electrolytic solution conductance measurements demonstrated the molecular formulas of the prepared Ru(III) complexes. A distorted octahedron stereochemistry was proposed for these six-coordinate naphthaldiimine-based Ru(III) complexes. Processing of X-ray diffraction data of 1 and 2 by the computer program Expo 2014 confirmed the final structural formulas that were determined based on spectroscopic and magnetic studies. The catalytic potential of the newly synthesized naphthaldiimine-based Ru(III) complexes in the hydrogenation of 1-hexene and cyclohexene was investigated. The Ru(III) catalysts catalyzed the double bond migration of 1-hexene to give trans-2-hexene which catalytically isomerizes to the stereo isomer cis-2-hexene. The induction step of the catalytic cycle is the formation of the actual catalyst, metal hydride (Ru(III)-H), that was generated in situ during the hydrogenation reaction. Several parameters controlling the catalytic reactions including the structure of the Ru(III) complex, the phase type of catalysis, and the quantity and nature of the solvents used were investigated. Various experiments made it possible to suggest a mechanism for the hydrogenation reactions.

Hydrogenation of cyclohexene catalyzed by nanoporous SPE-PtNi/C membrane electrode

Implementing large-scale synthesis of nanoporous PtNi/C catalysts for hydrogenation processes of unsaturated organic compounds under atmospheric pressure at temperatures below 100 °C is an urgent task. In this paper, a nanoporous SPE-PtNi/C membrane electrode is prepared by ion beam sputtering, ultrasonic-assisted electrochemical dealloying, and hotpressing. Special attention is paid to the analysis of the electrochemical properties, phase structure, surface morphology, active constituent distribution, and catalytic efficiency for cyclohexene hydrogenation of the produced electrode in comparison with those of commercial Pt/C catalysts. The results show that the ultrasonic-assisted electrochemical etching temperature exerts the most significant effect on the catalytic activity of the catalyst under consideration. In particular, the treatment of PtNi/C in 0.7 mol/L HClO4 for 1.5 h at the optimized temperature of 50 °C enables one to increase the catalytic activity by 25.20% at decreasing the Pt-loading content by 88.85% compared with commercial Pt/C. Furthermore, the nanoporous structure of the PtNi/C surface allows the binding energy of Pt 4f7/2 to be reduced by 0.23 eV due to the Ni loss and the crystal plane shrinkage from NiPt, which enhances the compressive strain of the lattice structure of exposed Pt and increases the number of active sites. Finally, the use of a nanoporous SPE-PtNi/C membrane electrode could increase the yield of cyclohexene during the hydrogenation reaction by 179% at simultaneously improving the current efficiency by 69%.

Fe Exchanged Supported Phosphomolybdic Acid: Synthesis, Characterization and Low Temperature Water Mediated Hydrogenation of Cyclohexene

Fe Exchanged Supported Phosphomolybdic Acid: Synthesis, Characterization and Low Temperature Water Mediated Hydrogenation of Cyclohexene

Mechanistic insights on the catalytic hydrogenation of cyclohexene by ruthenium(III) N2O2 tetradentate Schiff-base complex

The work aimed at the mechanistic investigation of the catalytic hydrogenation of cyclohexene by a newly synthesized ruthenium(III) Schiff base complex, [RuLCl(H2O)], where L represents tetradentate N2O2 naphthaldiimine. Several physicochemical methods were used to characterize the target complex. Furthermore, it was observed that the catalytic activity relies mainly on solvent composition. On the other hand, the density functional theory (DFT) was applied to explore the mechanistic story of the catalytic reaction. The findings showed that the complex has two stable isomers (trans and cis), which serve as platforms for the destination toward the hydrogenation journey through the in-situ generation of the active catalysts. Accordingly, one can imagine them as robust and weak machines for cyclohexane production in the reaction vessel. Interestingly, the experimental and the theoretical total activation energies are so comparable which supports the validity of the mechanistic insights.

Modification of liquid film thickness by the action of centrifugal force in a falling film microreactor: Effect on the overall process performance of a catalytic cyclohexene hydrogenation

This work presents a process intensification strategy for mass transfer enhancement by developing a system that provides centrifugal acceleration to a falling film microreactor (FFMR). The effective interfacial area for mass transfer was increased by modifying the liquid film at varying flow rates due to the applied centrifugal force's influence. The Nusselt and Kapitza correlations often utilized in predicting liquid film thickness were modified to account for an externally induced force acting normal to the flow direction. Consequently, the effect on film thickness was quantified, enabling the assessment of the overall process performance at different rotational speeds of the reactor unit.For this purpose, hydrogenation of cyclohexene conducted over a Pt/Al2O3 catalyst coated on the micro channel's surface was used as a model reaction. Overall process performance was significantly improved, and mass transfer rate was enhanced by a factor of more than 4.

Experimental and computational kinetics study of the liquid-phase hydrogenation of C[dbnd]C and C[dbnd]O bonds

Solvent effects on adsorption equilibrium and reaction kinetics are evaluated for hydrogenation reactions catalyzed by Pd/alumina in a series of different solvents. Three reactants – cyclohexene, benzene and benzaldehyde – and three solvents – n-heptane (HEP), methylcyclohexane (MCHA), decalin (DL) – have been investigated. Kinetic analysis of hydrogenation of cyclohexene reveals that hydrogen adsorbs on different sites from those where cyclohexene and the solvents adsorb; however, the presence of hydrogen on these separate sites affects the heats of adsorption of the hydrocarbons. When the solvent is a weakly interacting linear alkane (HEP), the rate determining step of the reaction is the first hydrogenation of adsorbed cyclohexene. This conclusion is supported by DFT calculations that show a higher enthalpy barrier for the first hydrogenation than for the second, while statistical thermodynamics analysis validates the physical significance of the entropy of adsorption parameters derived from the kinetic fitting of experimental data. By contrast, with solvents such as MCHA and DL, which interact more strongly with the metal surface and compete for active sites with the reactant and the surface intermediate, the rate limiting step seems to shift to the second hydrogenation step.One of the main conclusions of the study is that the effects observed with non-polar solvents are mostly due to competitive adsorption of the solvent, which causes a decrease in surface coverage of reactants and surface intermediates. Indeed, under identical conditions, the hydrogenation rates of CC bonds in cyclohexene (or the aromatic ring in benzene) follow the order HEP > MCHA > DL, which is consistent with the strongest solvent/metal interaction for DL and the weakest for HEP. Further, binary solvent mixtures of DL-HEP exhibit non-idealities that are clearly evident in the fitting of hydrogenation rates. It is proposed that the higher activity coefficient of liquid DL in the liquid mixture enhances its surface coverage, competing more effectively with the reactant, which causes a decrease in catalytic activity larger than that predicted assuming an ideal mixture of solvents.Likewise, large drops in benzene hydrogenation rates are observed in water-organic co-solvent mixtures due to the competitive adsorption of water on the Pd surface. Water adsorption is further enhanced by the non-ideality of the water-organic mixture. By contrast, in the hydrogenation of the CO bond of benzaldehyde, the presence of water provides a favorable alternative reaction path with lower activation barrier, resulting in higher hydrogenation activity when the reactant is a carbonyl-containing molecule, such as benzaldehyde. In this system, the H-bonded water network assists shuttling a proton from the Pd surface to the hydrophilic O atom in CO, assisted by surface charge separation. Since this H transfer pathway cannot take place with CC bonds or aromatic rings, only site inhibition occurs for these reactions.

Palladium(II) based imines; synthesis, characterization, X-Ray structural analysis; DFT and catalytic hydrogenation study

Based on the bridge alkyl chain length between the two azomethine linkages of the bis ortho naphtholimine ligands, two synthetic techniques were used to prepare a novel series of palladium(II) complexes. The molecular formulae of the isolated metal chelates were assigned based on thermal analysis (TGA and DTA) and analytical data. In addition comprehensive spectroscopic studies such as UV-Vis, IR, PXRD and X-ray single crystal have completed the structural formulations of the newly synthesized palladium(II) complexes in question. The best description of the overall molecular geometry of the palladium(II) center is the square planar as expected for the d8 center of palladium(II). DFT calculations were performed to correlate the structural properties of the present palladium(II) complexes with their catalytic activity towards the hydrogenation of cyclohexene. In addition, the optimized geometrical parameters deduced from the X-ray measurements for structural analysis are compared with the corresponding ones obtained by DFT calculations. Regarding complex 3, DFT calculations were carried out to decide the most appropriate molecular structure. The current square planar diimine palladium(II) complexes have been evaluated for the catalytic hydrogenation of mono olefin cyclohexene. The catalytic activity was studied in relation to the effect of catalyst structure, catalysis type, nature and amount of the solvents and co-solvents. The results obtained indicated that these complexes are pre-catalysts that efficiently catalyze hydrogenation of cyclohexene by H2 at mild conditions.