Partial Hydrogenation Of Benzene Research Articles

Effect of ZnSO4, MnSO4 and FeSO4 on the Partial Hydrogenation of Benzene over Nano Ru-Based Catalysts.

Nano Ru-based catalysts, including monometallic Ru and Ru-Zn nanoparticles, were synthesized via a precipitation method. The prepared catalysts were evaluated on partial hydrogenation of benzene towards cyclohexene generation, during which the effect of reaction modifiers, i.e., ZnSO4, MnSO4, and FeSO4, was investigated. The fresh and the spent catalysts were thoroughly characterized by XRD, TEM, SEM, XPS, XRF, and DFT studies. It was found that Zn2+ or Fe2+ could be adsorbed on the surface of a monometallic Ru catalyst, where a stabilized complex could be formed between the cations and the cyclohexene. This led to an enhancement of catalytic selectivity towards cyclohexene. Furthermore, electron transfer was observed from Zn2+ or Fe2+ to Ru, hindering the catalytic activity towards benzene hydrogenation. In comparison, very few Mn2+ cations were adsorbed on the Ru surface, for which no cyclohexene could be detected. On the other hand, for Ru-Zn catalyst, Zn existed as rodlike ZnO. The added ZnSO4 and FeSO4 could react with ZnO to generate (Zn(OH)2)5(ZnSO4)(H2O) and basic Fe sulfate, respectively. This further benefited the adsorption of Zn2+ or Fe2+, leading to the decrease of catalytic activity towards benzene conversion and the increase of selectivity towards cyclohexene synthesis. When 0.57 mol·L−1 of ZnSO4 was applied, the highest cyclohexene yield of 62.6% was achieved. When MnSO4 was used as a reaction modifier, H2SO4 could be generated in the slurry via its hydrolysis, which reacted with ZnO to form ZnSO4. The selectivity towards cyclohexene formation was then improved by the adsorbed Zn2+.

Surface investigation by X-ray photoelectron spectroscopy of Ru-Zn catalysts for the partial hydrogenation of benzene

Partial hydrogenation of benzene with ruthenium-supported catalysts is an interesting alternative route to produce cyclohexene, an intermediate in the production of nylon 6.6 and other fine chemicals. In this work, ruthenium chloride solution was added to xZnO/Al2O3 by wetness impregnation. The supports were derived from hydrotalcite compounds and tested on the partial hydrogenation of benzene. The catalyst with 10 wt.% of ZnO (Ru10ZnAl) presented the best catalytic performance reaching total conversion in 40 min of the reaction, and a maximum yield of 35% using pure benzene (without water, salts or other additives). The samples were characterized by X-ray photoelectron spectroscopy (XPS), X-ray fluorescence (XRF), X-ray diffraction (XRD), temperature programmed reduction (TPR) and H2 Chemisorption. Metallic and partially reduced ruthenium surface species were identified on the surface of the Ru10ZnAl catalyst and the electronic vicinity of Ru is proposed to be responsible for promoting the cyclohexene desorption, revealing a synergistic effect. In this sense, the electronic surroundings modification of surface zinc species with ruthenium species, followed by reduction, was evidenced by using the Modified Auger Parameter (MAP). These species played an important role in the reaction.

Selective hydroalkylation of benzene over palladium supported Y-Zeolite: Effect of metal acid balance

Bifunctional Palladium (Pd) supported Y-zeolite, with SiO2/Al2O3 ratios 5, 12, 30 and 60, prepared by impregnation method were used for hydroalkylation of benzene. It is found that the reaction condition and catalyst composition influence the hydroalkylation activity and cyclohexylbenzene (CHB) selectivity. CHB selectivity of a hydroalkylation catalyst can be determined by the destiny of the intermediate cyclohexene formed by partial hydrogenation of benzene on the metal site of the catalyst. That is, if the intermediate cyclohexene hydrogenates to cyclohexane on the metal site, the selectivity for CHB decreases whereas, if the intermediate cyclohexene is alkylated with benzene on the acid sites, the selectivity for CHB increases. Thus, there is a requirement of optimum balance of exposed metal and acid sites of the catalyst for enhancing CHB selectivity. At 42.2% of benzene conversion, Pd (0.2wt%)/HY5 (SiO2/Al2O3=5) catalyst gave a CHB selectivity of 75% in comparison to 70.3% for the best patented catalyst. Furthermore, a kinetic model has been developed for the hydroalkylation of benzene, assuming dissociative, non-competitive addition of hydrogen. Finally, the developed kinetic model along with experimental data was used to study the effect of mole ratio of acid sites to exposed metal sites of Pd/HY catalyst system for hydroalkylation reaction. Based on these results, the ratio of number of acid sites to exposed metal sites can be tuned to maximize CHB yield.

Challenging Thermodynamics: Hydrogenation of Benzene to 1,3‐Cyclohexadiene by Ru@Pt Nanoparticles

AbstractSince the earliest reports on catalytic benzene hydrogenation, 1,3‐cyclohexadiene and cyclohexene have been proposed as key intermediates. However, the former has never been obtained with remarkable selectivity. Herein, we report the first partial hydrogenation of benzene towards 1,3‐cyclohexadiene under mild conditions in a catalytic biphasic system consisting of Ru@Pt nanoparticles (NPs) in ionic liquid (IL). The tandem reduction of [Ru(COD)(2‐methylallyl)2] (COD=1,5‐cyclooctadiene) followed by decomposition of [Pt2(dba)3] (dba=dibenzylideneacetone) in 1‐n‐butyl‐3‐methylimidazolium hexafluorophosphate (BMI⋅PF6) IL under hydrogen affords core–shell Ru@Pt NPs of 2.9±0.2 nm. The hydrogenation of benzene (60 °C, 6 bar of H2) dissolved in n‐heptane by these bimetallic NPs in BMI⋅PF6 affords 1,3‐cyclohexadiene with an unprecedented 21 % selectivity at 5 % benzene conversion. Conversely, almost no 1,3‐cyclohexadiene was observed when using monometallic Pt0 or Ru0 NPs under the same reaction conditions and benzene conversions. This study reveals that the selectivity is related to synergetic effects of the bimetallic composition of the catalyst material as well as to the performance under biphasic reaction conditions. It is proposed that colloidal metal catalysts in ILs and under multiphase conditions (“dynamic asymmetric mixtures”) can operate far from the thermodynamic equilibrium akin to chemically active membranes.

Partial hydrogenation of benzene to cyclohexene over Ru/γ-Al2O3 nanocatalyst via w/o microemulsion using boric acid and ethanolamine additives

Ru/γ-Al2O3 nanocatalyst was synthesized by water-in-oil reverse microemulsion technique and characterized by TEM, SEM–EDX, XRD, N2 adsorption–desorption, and H2 chemisorption. The surface area and active sites (S M) of 3 wt% Ru/γ-Al2O3 was obtained around 217.6 m2/g and 45.70 m2/gcat, respectively. The catalyst performance of Ru/γ-Al2O3 was assessed in the selective hydrogenation benzene to cyclohexene in the presence of boric acid (BA) and ethanolamine (EA) additives. The effect of such specific additives alone and in combination on the activity and selectivity of benzene hydrogenation was systematically investigated. Ru catalyst displayed pre-eminent performance at 0.5 mmol ratio of BA to EA exhibiting the highest selectivity (40 %) and yield (16 %) of the intermediate product, cyclohexene at 40 % of benzene conversion.

Doping effects of B in ZrO2 on structural and catalytic properties of Ru/B-ZrO2 catalysts for benzene partial hydrogenation

The B-doped ZrO2 (B-ZrO2) samples with different B/Zr ratios were synthesized using zirconium oxychloride and boric acid as the precursors. Their crystallographic phase retained as tetragonal ZrO2 after the doping of B; however, the amount of the Lewis acid sites increased from 46.1μmolNH3g−1 on ZrO2 to 100.6μmolNH3g−1 on B-ZrO2(1/10) with the nominal B/Zr molar ratio of 1/10. The Ru/B-ZrO2 catalysts were then prepared by chemical reduction, and their electronic and structural properties were systematically characterized by spectroscopic techniques. It is identified that the Ru nanoparticles (NPs) supported on these B-ZrO2 samples exhibited similar size, chemical state, and microstructure. In the partial hydrogenation of benzene, the turnover frequency of benzene was linearly proportional to the amount of the acid sites on the supports, whereas the selectivity toward cyclohexene displayed a volcanic evolution passing through a maximum of 88% on the Ru/B-ZrO2(1/15) catalyst. Kinetic analysis indicated that the acid sites improved the rate constants of the benzene to cyclohexene step (k1) and the cyclohexene to cyclohexane step (k2) to different degrees. The resulting k1/k2 ratio increased from 3.7×10−2lmol−1 (Ru/ZrO2) to 4.8×10−2lmol−1 (Ru/B-ZrO2(1/15)), and then declined to 4.1×10−2lmol−1 (Ru/B-ZrO2(1/10)), which explained the volcanic evolution of the selectivity toward cyclohexene with respect to the acid amount.

The influence of transition metal ions on the catalytic performance of Ru particles during the liquid phase hydrogenation of benzene to cyclohexene

The influence of some transition metal ions including Fe2+, Ni2+, Cr3+, Mn2+, Zn2+, Cd2+ on the catalytic performance of Ru particles during the liquid phase partial hydrogenation of benzene to cyclohexene was investigated in a titanium autoclave and a stainless steel autoclave. The Ru particles were prepared by the precipitation method. The catalysts were characterized using XRD, BET surface area measurement and XPS. The structure configurations and formation enthalpies of the hydrated metal ions, the complexes of the metal ions with benzene and cyclohexene as well as the complexes of hydrated metal ions with benzene and cyclohexene were optimized and evaluated using quantum chemical calculation methods. It was found that the poisoning effect of the transition metal ions on the catalytic activity of Ru particles only partially obeys the “Maxted rule”. The enhancing effect of the transition metal ions on the cyclohexene selectivity is associated with both the interaction of the metal ions with the active sites on Ru surface and with the tendency of metal ions to form hydrated complexes. In the stainless steel autoclave, the Fe2+, Ni2+ and Cr3+ resulted from the corrosion of the stainless steel have a synergetic effect with Zn2+, leading to a higher selectivity to cyclohexene.

Ru/ZrO<sub>2</sub>催化剂在苯部分加氢反应中的粒径效应

The particle size effect on partial hydrogenation of benzene to cyclohexene over Ru/ZrO2 catalysts is reported. Uniform Ru nanoparticles (NPs) with a tunable particle size from 2.4 to 5.4 nm were synthesized by a polyol reduction method and deposited on ZrO2. The catalysts were characterized by ultraviolet-visible absorption spectroscopy (UV-Vis), N2 physisorption, H2 chemisorption, temperature-programmed desorption of H2 (H2-TPD), powder X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). It was found that the type of polyol and the concentration of additive (sodium acetate trihydrate) imposed remarkable effect on the particle size of Ru. A distinct particle size effect occurred in partial hydrogenation of benzene. With the size of the Ru NPs increasing, the hydrogenation activity of benzene increased, and the initial selectivity ( S 0) to cyclohexene showed a volcanic-type variation tendency, which revealed that the optimal Ru size for obtaining the highest S 0 is 4.4 nm. The Ru/ZrO2 catalyst reduced by 1,2-propanediol exhibited the highest S 0 (82%) and the yield of cyclohexene (39%). Based on the characterization results, the size effect of Ru on the activity and selectivity is discussed.

Partial hydrogenation of benzene on Ru catalysts: Effects of additives in the reaction medium

The partial hydrogenation of benzene is an interesting chemical reaction mostly because of cyclohexene, a compound that can be part of the production chain of many other chemicals. In the present work, it was investigated the effects of additives in the reaction medium on the performance of Ru/Al2O3 and Ru/CeO2 catalysts for the partial hydrogenation of benzene in liquid phase. The Ru catalysts were prepared by incipient impregnation or wet impregnation, both from aqueous solution of the precursor RuCl3·xH2O. The catalysts prepared by incipient impregnation were reduced at 573K under H2 flow, whereas formaldehyde was used to reduce the catalysts prepared by wet impregnation. The solids were characterized by potentiometric titration, N2 physisorption, SEM, TEM, EDX, XPS and TPR. The catalytic performance in the liquid phase was evaluated using a slurry Parr reactor at 373K and under 5MPa of H2 pressure. The additives studied were the following: ethylenediamine, ethyl acetate, n-methyl-2-pyrrolidone, monoethyleneglycol and monoethanolamine. The results indicate that the Ru/Al2O3 catalyst, prepared by wet impregnation, leads to the highest values of activity and selectivity. The yield of cyclohexene follows the order: monoethanolamine>monoethyleneglycol>n-methyl-2-pyrrolidone≫ethyl acetate>without additive≫ethylenediamine.

Partial hydrogenation of benzene over the metallic Zn modified Ru-based catalyst

From the adsorption point of view, partial hydrogenation of benzene to cyclohexene over the metallic Zn modified Ru-based catalyst was experimentally and theoretically investigated. A decreased hydrogenation activity but increased selectivity to cyclohexene over the prepared Ru-Zn/ZrO 2 catalyst was observed in the partial hydrogenation of benzene. Theoretical calculations suggest that the above phenomena are mainly resulted from the depression of the chemisorption of benzene and cyclohexene on the modified catalyst, especially for the latter. Undesired deep hydrogenation from cyclohexene to cyclohexane in the middle and late reaction stage therefore is effectively retarded, by which an improved cyclohexene yield is guaranteed. An optimal Zn content of 2.72 wt.% in the Ru-based catalyst was proposed by both the experiment and calculation for the partial hydrogenation of benzene, and a cyclohexene yield up to 44% was obtained over Ru-Zn/ZrO 2 catalyst.

Fabrication of a Pt Nano-cluster/Photosensitive Polyimide Hybrid Membrane Reactor and Its Partial Hydrogenation of Benzene

Abstract The partial hydrogenation of benzene by a Pt nano-cluster/photosensitive polyimide (Pt/PSPI) hybrid membrane was investigated. Monodisperse Pt nano-clusters were obtained by microwave-assisted reduction of H 2 PtCl 6 with ethylene glycol. Transmission electron microscopy showed that the average diameter of the Pt nanoparticles was 3.7 nm. The Pt/PSPI hybrid catalyst gave a high selectivity for cyclohexene of 72.4% in the liquid phase hydrogenation of benzene.

Dehydrogenation of Cyclohexanol to Cyclohexanone: Influence of Methylcyclopentanols on the Impurities Obtained in ε-Caprolactam

The most representative impurities in e-caprolactam produced from cyclohexanol obtained by partial hydrogenation of benzene are the δ-valerolactams. These impurities come from the dehydrogenation−o...

Partial liquid-phase hydrogenation of benzene to cylohexene on SiO2-immobilized lanthanide (Eu and Yb) catalysts

SiO2-immobilized Eu and Yb catalysts (≡Si–O–Ln–NH2) obtained by the reaction of surface hydroxyl groups on SiO2 with lanthanide metals dissolved in liquid ammonia are active for the partial liquid-phase hydrogenation of benzene to cyclohexene when the reaction was carried out at 423–483 K with hydrogen pressures of 1–5 MPa. Interestingly, only divalent amides are catalytically effective for the partial hydrogenation of benzene.

Effect of Preparation on Ru−Zn Ultrafine Catalysts in Partial Hydrogenation of Benzene

A series of ultrafine Ru−Zn catalysts have been prepared with direct reduction and hydroxide methods with various Ru/Zn ratios. Sodium borohydride was used as a reducing agent to avoid the agglomeration problem posed by the high reduction temperature when using hydrogen as a reducing agent. The preparation method has a great effect on the composition and surface area of the catalyst. The catalysts prepared with the hydroxide method gave a lower surface area. However, it showed high activity of benzene disappearance. The performance of Ru−Zn catalysts prepared with the hydroxide method display a more distinctive behavior in benzene hydrogenation upon variation of the atomic ratio of ruthenium to zinc. The catalysts prepared with the hydroxide method were more selective to cyclohexene than those prepared with the direct reduction method. The Ru/Zn ratio also has a great influence on the selectivity to cyclohexene.

Partial Hydrogenation of Benzene on Ru-Zn Nanoparticle Catalysts (Short Communication)

A series of ruthenium-zinc catalysts with various Ru/Zn ratios were synthesized. These catalysts were characterized with elemental analysis, nitrogen sorption and transmission electron microscopy (TEM). The results of nitrogen sorption and TEM show that these samples were nano-size. Partial hydrogenation reaction of benzene over these catalysts was carried out in a batch reactor at 625 psig and 425 K. Large amount of water and zinc sulfate were used to have high yield of cyclohexene. The activity of benzene hydrogenation decreased with an increase of the Zn content. However, the selectivity and the yield to cyclohexene significantly increased with an increase of the Zn content. Ruthenium and zinc should be in a close proximity so that the catalytic behavior of ruthenium is altered in a delicate way.

Benzene-selective hydrogenation to cyclohexene over supported ruthenium boride catalysts prepared by a novel method

Supported amorphous ruthenium boride catalysts, prepared by a novel method that does not require any modifiers in the reaction system, are able to convert benzene to cyclohexene with high yields when the partial hydrogenation of benzene is carried out in the liquid phase.

Properties of Ruthenium Catalyst Prepared by a Chemical Mixing Procedure

Three types of catalysts, (A) chemically mixed catalyst activated in hydrogen after calcination, (B) chemically mixed catalyst activated in hydrogen without calcination, and (C) impregnated catalyst activated in hydrogen without calcination, were prepared. Their properties were investigated and compared, so as to elucidate the reasons why type (B) catalyst is the most effective for the formation of cyclohexene in the partial hydrogenation of benzene.Measurements of TGA, FT-IR, XRD, EM, hydrogen and carbon monoxide adsorptions indicated differences among the three types of the ruthenium catalysts : (1) type (B) catalyst contains diols used in its preparation, (2) active components (Ru, Cu) in the type (B) catalyst are highly dispersed compared with the other two catalysts, (3) the hydrogen absorption capacity of type (B) catalyst is much lower than its carbon monoxide absorption capacity, and (4) the carbon monoxide absorption capacity of type (C) catalyst is essentially the same as its hydrogen absorption capacity.From these findings, the diols remaining in type (B) catalyst following activation are considered to help prevent active components from aggregating by linking them to a support (Si) as a bridging ligand and to depress the formation of cyclohexane by reducing the hydrogen absorption capacity of ruthenium through coordination of the hydroxy groups. Type (B) catalyst is thus concluded to give high activity and cyclohexene yield in the partial hydrogenation of benzene.

Cyclohexanol Formation via Partial Hydrogenation of Benzene

In the two-step process for manufacturing cyclohexanol via cyclohexene from benzene, the procedure for effectively hydrating cyclohexene only in a reaction mixture obtained by partial hydrogenation of benzene is very important. This is because separating cyclohexene from the reaction mixture obtained in the first step is much more difficult than recovering benzene and cyclohexane after converting cyclohexene to cyclohexanol in the second step. Therefore, we investigated the optimum hydration conditions to obtaind cyclohexanol from a mixture using sulfuric acid and an additive. At a reaction temperature below 30°C, both the hydration rate and cyclohexanol yield decreased with lowering of the temperature. At a temperature over 30°C, the sulfonation of benzene and polymerization of cyclohexene easily occurred. Essentially the same was observed at the concentration and amount of sulfuric acid. Thus, the optimum temperature, sulfuric acid concentration and the used hydration were 30°C, 75%, and 2.7 mole to 1 mole of cyclohexene, respectively. As additives all metal salts were effective, but no alcohol used at this stage promoted cyclohexanol formation. The best additive was nickel sulfate. When a mixture of benzene (0.05mol), cyclohexene (0.15mol) and cyclohexane (0.3mol) was treated with 75% sulfuric acid (0.4mol) in the presence of nickel sulfate (0.01mol) at 30°C for 35h, the cyclohexanol yield was about 80%.

Effect of Impregnation Solvents in the Preparation of Ru/SiO2 Catalysts on the Partial Hydrogenation of Benzene

Ru/SiO2 catalysts were prepared by impregnating RuCl3·nH2O into silica in a series of solvents which can coordinate to metal ions and activating in hydrogen. The effects of the im-pregnation solvents on the Ru/SiO2 catalyzed hydrogenation of benzene were investigated. In the catalysts activated in hydrogen without calcination, cyclohexene yields were in the range of 9 to 25 depending on the complexing ability of the preparation solvents. When the impregnation solvents had strong coordination ability, the catalysts showed low cyclohexene yields. But when the impregnation solvents had weak coordination ability, the catalysts showed high cyclohexene yields. For instance, 2-aminoethanol and ethanol gave the catalysts showing the highest and lowest cyclohexene yields respectively. When the catalysts were activated in hydrogen after cal-cination, all the catalysts showed almost the same cyclohexene yields in spite of the different kinds of impregnation solvents. The visible spectra of the catalyst preparation solutions and thermogravimetric analyses of non-calcined catalysts indicated that differences between the catalysts with and without calcination is due to inclusion of impregnation solvents in non-calcinated catalysts after activation.

Selective lanthanide-catalysed reactions. Catalytic properties of Sm and Yb metal vapour deposition products

The characteristics of lanthanide catalysts obtained when Sm and Yb were vaporized into a frozen organic (tetrahydrofuran, benzene and methyl-cyclohexane) matrix (77 K) were investigated. These low-valent, highly dispersed lanthanide particles (indicated as Sm/THF, Sm/benzene, Yb/THF, Yb/benzene etc.) were catalytically active and selective for hydrogenation and isomerization. Samarium usually showed a greater activity than ytterbium. Olefin [ethene, propene, but-1-ene and (z)-but-2-ene] hydrogenation obeyed the rate law v=kPH, suggesting that the reaction is controlled by catalytic activation of hydrogen. The molecular isotopic identity of hydrogen was conserved during the hydrogenation. Yb/THF and Yb/benzene were active for partial hydrogenation of benzene to cyclohexene. For the hydrogenation of olefins and acetylenes the substrate specificity was high; thus C—C double bonds were more readily reduced than triple bonds. The samarium and ytterbium catalysts discriminate between terminal and internal C—C triple bonds, only internal CC bonds (but-2-yne and pent-2-yne) being reduced very selectively in contrast to acetylene, methylacetylene and but-1-yne. Solid base character of the lanthanide provides a cause for these differences in catalytic properties.