Cyclohexene Selectivity Research Articles

Ru-Zn catalysts for selective hydrogenation of benzene using coprecipitation in low alkalinity

Several unsupported Ru-Zn catalysts were successfully prepared using the coprecipitation method under low alkaline conditions, and their catalytic performance was evaluated for the selective liquid-phase hydrogenation of benzene. The effect of the amount of ZnCl2 added to the coprecipitation solution on the physical and catalytic properties of the Ru-Zn catalysts was studied whilst keeping the amount of the NaOH precipitant constant. The properties of the resulting catalysts were characterized by N2 adsorption, X-ray diffraction, and temperature-programmed reduction. The effects of the stirring rate and the amount of ZnSO4 additive on the catalytic properties of the Ru-Zn catalysts were investigated using the optimal Zn content. The recyclability of the optimal Ru-Zn catalyst was also explored. The results revealed that the optimal Zn content for the Ru-Zn catalysts was 16.7 wt%, and the selectivity for cyclohexene could reach up to 80% (yield > 45%) when the benzene conversion was 57% in an aqueous solution of ZnSO4 (0.45 mol/L) under the optimal reaction conditions (i.e., hastelloy reactor, 1200 r/min, 150 °C and 5 MPa of H2 pressure). The presence of ZnO crystals in the Ru catalysts was found to be critical to obtaining high selectivity for cyclohexene (>80%). The Ru-Zn catalysts prepared under the low alkaline conditions also showed good stability, which indicates that they could potentially be used for industrial application.

Partial Hydrogenation of Benzene to Cyclohexene over Ru‐Zn/MCM‐41

Ru‐Zn/MCM‐41 catalysts for the partial hydrogenation of benzene with differing Zn contents were prepared by the incipient‐wetness impregnation method. The evaluation results indicate that Zn simultaneously depresses the catalysts activity and cyclohexene selectivity. This can be attributed to the change in the amount of the different hydrogenation sites affected by Zn. The weak hydrogenation sites can promote benzene conversion, and the strong hydrogenation sites, a novel kind of hydrogenation site found on the surface of the catalysts under the influence of Zn, are beneficial for cyclohexene hydrogenation.

Hydrodeoxygenation of Bio-Oil on Bimetallic Catalysts: From Model Compound to Real Feed

Two series of bimetallic Ni-Co catalysts and corresponding monometallic catalysts with ca. 20 wt% metal loading were evaluated in hydrodeoxygenation (HDO) of phenol as a model compound for bio-oil. The bimetallic catalysts outperformed the corresponding monometallic catalyst in terms of conversion and cyclohexane selectivity. This could be attributed to the formation of Ni-Co alloy, which caused a decrease in metal particle size and stabilized Ni active sites in the near surface region. The balanced combination of formed Ni-Co alloy with acidity from supports allowed performing all individual steps in the reaction network toward desired products at high rate. Consequently, the two best-performing catalysts were tested in HDO of wood based bio-oil, showing that the bimetallic catalyst 10Ni10Co/HZSM-5 was more effective than 20Ni/HZSM-5 in terms of degree of deoxygenation and upgraded bio-oil yield. These findings might open an opportunity for development of a novel cheap but effective catalyst for a key step in the process chain from biomass to renewable liquid fuels.

Hydrodeoxygenation of phenol as a bio-oil model compound over intimate contact noble metal–Ni2P/SiO2 catalysts

1% Pd–10% Ni2P/SiO2, from a Ni2P reducing noble metal precursor, presents a high activity and cyclohexanol or cyclohexane selectivity due to more active sites and electrons transferring from Ni2P to the noble metal.

Solventless hydrogenation of benzene to cyclohexane over a heterogeneous Ru–Pt bimetallic catalyst

The hydrogenation of benzene to cyclohexane has attracted renewed attention in the chemical and petroleum industry, due to its application in the synthesis of many useful chemical intermediates. However, the development of highly efficient hydrogenation processes under mild solvent-free conditions is still a great challenge. Herein, we report a highly efficient Ru–Pt bimetallic catalyst, which was deposited on a zeolite-type MOF (MIL-101) by a simple colloidal deposition method, for neat benzene hydrogenation to cyclohexane. The catalyst system was shown to be able to provide excellent activities with a high selectivity for cyclohexane (in up to >99% yield). The enhanced reactivity is rationalized in terms of the synergy of Ru and Pt. The kinetics of neat benzene hydrogenation by the Ru–Pt/MIL-101 catalyst was investigated. The reaction showed a zero-order dependence on benzene while a first-order dependence on H2 pressure. A kinetic model of hydrogenation of neat benzene over the Ru–Pt catalyst was established based on the experimental results.

Selective vapor-phase hydrodeoxygenation of anisole to benzene on molybdenum carbide catalysts

Vapor-phase hydrodeoxygenation (HDO) of anisole over Mo2C catalysts at low temperatures (420–520K) and ambient pressure showed (1) remarkable selectivity for C–O bond cleavage, giving benzene selectivity >90% among C6+ products, (2) high hydrogen efficiency for the HDO reaction as indicated by low cyclohexane selectivity (<9%), and (3) good stability over ∼50h. Methane selectivity increased at the expense of methanol selectivity as anisole conversion increased, suggesting that the phenolic C–O bond was cleaved preferentially. The concurrent near half-/zero-order dependence of benzene synthesis rates on H2/anisole pressure, and the preferential inhibition of benzene synthesis rates upon introduction of CO relative to isotopic HD exchange suggest that catalytic sites for H2 activation are distinct from those required for the activation of anisole. The involvement of metallic sites on Mo2C catalysts for this reaction was demonstrated by the nearly invariant benzene synthesis rate per CO chemisorption site.

Effect of calcination temperature of Ni/SiO2-ZrO2 catalyst on its hydrodeoxygenation of guaiacol

SiO 2 -ZrO 2 composites were synthesized by chemical precipitation and used to prepare a series of bifunctional Ni/SiO 2 -ZrO 2 catalysts by impregnation. The effect of calcination temperature on the catalyst structure and its catalysis of the hydrodeoxygenation of guaiacol was investigated. Guaiacol was converted to cyclohexane by a synergism between the metal center and solid acid support. The catalyst calcined at 500 °C gave a maximum 100% guaiacol conversion and 96.8% selectivity for cyclohexane. The catalyst samples were characterized by N 2 adsorption, H 2 chemisorption, X-ray diffraction, H 2 temperature-programmed reduction, NH 3 temperature-programmed desorption, and Raman spectroscopy. The synthesized SiO 2 -ZrO 2 was an amorphous oxide. The Ni/SiO 2 -ZrO 2 catalyst calcined at 500 °C has more acidity, smaller NiO particles, and larger BET surface area and pore volume, which gave it the best catalytic performance. Cyclohexane was obtained with high selectivity by the hydrodeoxygenation of guaiacol over a bifunctional Ni/SiO 2 -ZrO 2 catalyst. The catalytic performance was influenced significantly by the calcination temperature of the catalyst.

Influence of Preparation Conditions on the Structure of MCM-41 and Catalytic Performance of Ru/MCM-41 in Benzene Hydrogenation

The influence of the preparation conditions on the structures of mesoporous molecular sieve MCM-41 were studied. The prepared MCM-41 samples were characterised by nitrogen physical adsorption–desorption, powder X-ray diffraction, transmission electron microscopy, FT-IR spectroscopy, thermo gravimetric analysis, differential scanning calorimetry and water/benzene static adsorption technologies. Ru/MCM-41 catalysts were then prepared by double solvent impregnation method and tested for benzene hydrogenation to cyclohexene. The structure characteristics of MCM-41 have a great effect on cyclohexene selectivity in benzene hydrogenation process. Ruthenium supported on MCM-41 with moderate surface area, larger pore size and pore volume, better long-range-order of hexagonal mesoporous shows better catalytic performance for benzene hydrogenation to cyclohexene.

Benzene hydrogenation over oxide-modified MCM-41 supported ruthenium–lanthanum catalyst: The influence of zirconia crystal form and surface hydrophilicity

The effects of the preparation conditions on the crystal form and surface properties of zirconia were studied. Mesoporous MCM-41 modified by tetragonal and monoclinic zirconia were synthesized by hydrothermal and precipitation methods. Then MCM-41 and zirconia-modified MCM-41 supported ruthenium–lanthanum catalysts were prepared via cyclohexane–water double solvent impregnation method. The obtained supports and catalysts were characterized by powder X-ray diffraction, transmission electron microscopy, energy dispersive X-ray spectroscopy, N2 adsorption–desorption, thermogravimetric and differential scanning calorimetry, temperature programmed desorption of NH3, static water/benzene adsorption techniques. It has been found that MCM-41 modified by tetragonal zirconia with exclusive Lewis-acidic sites exhibits more surface hydroxyl groups and higher hydrophilicity than MCM-41 modified by monoclinic and amorphous zirconia. Tetragonal zirconia-modified MCM-41 supported ruthenium–lanthanum catalyst shows better catalytic performance in benzene hydrogenation to cyclohexene with benzene conversion of 54.4% and cyclohexene selectivity of 84.7%.

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.

Partial Hydrogenation of Benzene to Cyclohexene over Novel Ru-B/MOF Catalysts

制备了多种金属-有机骨架（MOF）材料，采用浸渍-化学还原法制备了非晶态Ru．B／MOF催化剂，考察了它们在苯部分加氢反应中的催化性能．催化性能评价结果表明，这些催化剂的初始反应速率（r0）顺序为Ru．B／MIL-53（AI）〉Ru-B／MIL-53（AI）-NH2〉RU—B／UIO．66（Zr）〉Ru—B／UIO．66（Zr）-NH2〉Ru-B／MIL-53（Cr）〉Ru．B／MIL-101（Cr）〉〉Ru—B／MIL-100（Fe），环己烯初始选择性（＆）顺序为Ru．B／MIL-53（AI）≈Ru．B／MIL-53（Cr）〉Ru．B／UIO-66（Zr）-NH2〉Ru—B／MIL-101（Cr）〉Ru-B／MIL-53（AI）-NH：〉Ru-B／UIO．66（Zr）≈Ru．B／MIL．100（Fe）．催化性能最好的Ru-B／MIL-53（AI）催化剂上的r0和So分别为23mmol·min^-1·g^-1和72％．采用多种手段，对催化性能差异最为显著的Ru—B／MIL-53（AI）和Ru-B／MIL-100（Fe）催化剂的物理化学性质进行了表征．发现MIL-53（Ai）载体能够更好地分散Ru-B纳米粒子，粒子的平均尺寸为3．2nm，而MIL-100（Fe）载体上Ru．B纳米粒子团聚严重，粒径达46．6nm．更小的粒径不仅能够提供更多的活性位，而且也有利于环己烯选择性的提高．对Ru—B／MIL．53（AI）催化剂的反应条件进行了优化，在180。C和5MPa的H：压力下，环己烯得率可达24％，展示了MOF材料用作苯部分加氢催化剂载体的良好前景．

Hydrodeoxygenation of Guaiacol over Nickel-based Catalyst Supported on Mixed Oxides

Using bimetal mixed oxides Al2O3-SiO2, Al2O3-T1O2, TiO2-SiO2 and TiO2-ZrO2 as supports, nickel catalysts were tested through hydrodeoxygenation ( HDO) reaction of guaiacol and characterized by Brunauer-Emmett-Teller( BET), X-ray diffraction( XRD), NH3 temperature programme desorption( NH3-TPD) and H-2 temperature programme reduction (H-2-TPR) techniques. The effects of support, solvent, reaction temperature and pressure on conversion of guaiacol and selectivity of different products were studied. The resistance of coke, recyclability of catalyst and the reaction mechanism for guaiacol hydrodeoxygenation were also discussed. The results show that the activities of Ni/TiO2-ZrO2 are obviously better than the others under the same reaction conditions. The conversion of guaiacol over Ni/TiO2-ZrO2 catalyst is 100% and the selectivity for cyclohexane is as high as 86.4% under the optimization condition of 300 degrees C and the initial H-2 pressure of 4 MPa in decalin. Moreover, the Ni/TiO2-ZrO(2)catalyst has a better performance of anti-coking than traditional catalysts, about only 3. 2% ( mass fraction) of residual cokes on the catalyst surface.

Selective hydrogenation of benzene to cyclohexene in continuous reaction device with two reaction reactors in serie over Ru-Co-B/ZrO2 catalysts

A Ru-B/ZrO 2 catalyst for selective hydrogenation of benzene to cyclohexene was prepared using a chemical reduction method. The effects of transition metals such as Cr, Mn, Fe, Co, Ni, Cu, and Zn on the performance of the Ru-B/ZrO 2 catalyst were investigated. It was found that the addition of these transition metals all increased the B content of the Ru-B/ZrO 2 catalyst. The modification of B, the ensemble effect, and the ligand effect of the second metal or metal oxide resulted in a decrease in the activity and an increase in the selectivity for cyclohexene of the Ru-B/ZrO 2 catalyst. When the atomic ratio of Co/Ru was 0.06, the Ru-Co-B/ZrO 2 catalyst gave a selectivity for cyclohexene of 82.8% and a cyclohexene yield of 62.8% at a benzene conversion of 75.8% at 25 min. Moreover, the benzene conversion was stable at around 40%, and the selectivity for cyclohexene and the cyclohexene yields stabilized at around 73% and 30%, respectively, in 419 h under the optimum reaction conditions in a continuous device with two reactors in series. The selectivity for cyclohexene and the cyclohexene yield were stabilized at around 73% and 30%, respectively, in 419 h over a Ru-Co-B/ZrO 2 catalyst in a continuous device with two reactors in series.

Catalytic Alkane Oxidation by Homogeneous and Silica-supported Cobalt(II) Complex Catalysts with a Triazolyl Group-containing Tetradentate Ligand

Abstract Homogeneous and heterogeneous cobalt complex catalysts with bis(pyridylmethyl)(triazolylmethyl)amine ligand were prepared. Although simple cobalt salts catalyze cyclohexane oxidation with mCPBA, the cyclohexane selectivity increases upon coordination of tetradentate ligands. In the heterogeneous catalysis, the yield and selectivity of cyclohexanol are improved with an increase in the ligand density on the silica support due to the suppression of metal leaching.

Structural and Catalytic Properties of Alkaline Post‐Treated Ru/ZrO2 Catalysts for Partial Hydrogenation of Benzene to Cyclohexene

AbstractPartial hydrogenation of benzene to cyclohexene is attractive in terms of feedstock accessibility, atomic economy, and operational simplicity. Herein, a series of Ru/ZrO2 catalysts were prepared by post‐treatment of a binary Ru–Zn/ZrO2 catalyst using 5–30 wt % NaOH aqueous solutions. Alloying between Ru and Zn was evidenced for the catalyst post‐treated only by water (Ru/ZrO2‐0). Alkaline post‐treatment removed metallic Zn, forming smaller Ru nanoparticles. Concomitantly, the hydrophilicity of the catalysts was increased and maximized on the 10 wt % NaOH‐treated catalyst (Ru/ZrO2‐10). In partial hydrogenation of benzene, the Ru/ZrO2‐0 catalyst displayed the highest turnover frequency but the lowest initial selectivity to cyclohexene, whereas the Ru/ZrO2‐10 catalyst exhibited the highest initial selectivity (86 %) and yield of cyclohexene (51 %) among the catalysts investigated. A quantitative relationship between the initial selectivity to cyclohexene and the hydrophilicity of these catalysts was identified, which rationalizes the significant impact of alkaline post‐treatment on selectivity enhancement in partial hydrogenation of benzene to cyclohexene over Ru/ZrO2 catalysts.

Effect of transition metals (Cr, Mn, Fe, Co, Ni, Cu and Zn) on the hydrogenation properties of benzene over Ru-based catalyst

The influence of transition metals on the hydrogenation properties of benzene over Ru-based catalysts had been investigated in the presence of ZnSO4 acting as the reaction modifier. It was found that the (Zn(OH)2)3(ZnSO4)(H2O)x salt (x=1 or 3) chemisorbed on Ru surface played a key role in improving the selectivity of Ru catalysts to cyclohexene. The promoter Cr in Ru–Cr(x) catalysts existed as Cr2O3. The amount of the (Zn(OH)2)3(ZnSO4)(H2O)x salt (x=1 or 3) chemisorbed on Ru surface slightly decreased with the increase of the amount of Cr2O3, resulting in a slight decrease of the selectivity to cyclohexene for the Ru–Cr(0.42) catalyst. Co and Ni promoters were present as Co3O4 and Ni(OH)2 in the Ru–Co(x) and Ru–Ni catalysts, respectively. Increasing amounts of Co3O4 and Ni(OH)2 increased the chemisorption of (Zn(OH)2)3(ZnSO4)(H2O)x salt (x=1 or 3), leading to a slight decrease in activity and a slight increase in selectivity of the Ru–Co(x) and Ru–Ni(x) catalysts to cyclohexene. The promoters Mn, Fe and Zn existed as Mn3O4, Fe3O4 and ZnO, respectively, in the Ru–Mn(x), Ru–Fe(x) and Ru–Zn(x) catalysts. These could react with ZnSO4 to form the (Zn(OH)2)3(ZnSO4)(H2O)x salt (x=1 or 3). The amount of chemisorbed (Zn(OH)2)3(ZnSO4)(H2O)x salt (x=1 or 3) was significantly increased with the content of Mn3O4, Fe3O4 and ZnO, resulting in a prominent decrease in activity and a significant increase in cyclohexene selectivity of the Ru–Mn(x), Ru–Fe(x) and Ru–Zn(x) catalysts. The Ru–Mn(0.23), the Ru–Fe(0.47) and the Ru–Zn(0.27) catalysts provided maximum cyclohexene yields of 55.3%, 56.7% and 53.4%, respectively. The Cu promoter in the Ru–Cu(0.49) catalyst was present as CuO. Part of the CuO could react with the ZnSO4 in the slurry to form a Cu4(SO4)(OH)6(H2O) salt. The presence of the chemisorbed Cu4(SO4)(OH)6(H2O) and (Zn(OH)2)3(ZnSO4)(H2O)x (x=1 or 3) salts improved the selectivity of the Ru–Cu(0.49) catalyst to cyclohexene.

Production of cyclohexane from lignin degradation compounds over Ni/ZrO2–SiO2 catalysts

The main products of lignin degradation are phenolic compounds. It is meaningful to study the processes by which cyclohexane is produced from phenolic compounds via hydrodeoxygenation (HDO), because it could be used as fuel additives, chemical feedstock and solvent. In this work, support material ZrO2–SiO2 mixed oxides with different Si/Zr ratio were synthesized, and a series of Ni/SiO2–ZrO2 catalysts with different Ni loading were prepared by impregnation method. The exploration of HDO process was carried out using phenol and guaiacol as model compounds. Effects of Si/Zr ratio, Ni loading and reaction temperature on conversion of phenol and guaiacol as well as distribution of HDO products were systematically investigated. The results showed that almost all of phenol and guaiacol could be effectively converted into O-free products. And the selectivity of cyclohexane was in excess of 90%.

Selective hydrogenation of benzene to cyclohexene over nanocomposite Ru-Mn/ZrO2 catalysts

A series of Ru-Mn catalysts with different Mn contents were prepared by coprecipitation, and their catalytic performance, using nanoscale ZrO2 as a dispersant, for the selective hydrogenation of benzene to cyclohexene was investigated. The catalysts were characterized using X-ray diffraction, transmission electron microscopy, N2 physisorption, X-ray fluorescence, atomic absorption spectroscopy, and Auger electron spectroscopy. The results confirmed that the Mn existed as Mn3O4 on the Ru surface. The Mn3O4 reacted with ZnSO4 to form an insoluble [Zn(OH)2]3(ZnSO4)(H2O)3 salt, which was readily chemisorbed on the Ru surface. This chemisorbed salt played a key role in improving the cyclohexene selectivity over the Ru catalyst. The cyclohexene yield of 61.3% was obtained over the Ru-Mn catalyst with the optimum Mn content of 5.4%. This catalyst had good stability and excellent reusability.

Hydrodeoxygenation of Phenol and Derivatives over an Ionic Liquid‐Like Copolymer Stabilized Nanocatalyst in Aqueous Media

AbstractUsing phenolic bio‐oil as feedstock for sustainable production of alkane fuels is of great significance. Here, the hydrodeoxygenation of phenol and its derivatives has been systematically investigated in aqueous media with a dual‐functional catalyst system consisting of water‐soluble, ionic liquid‐like copolymer A‐stabilized nanocatalysts and the mineral acid H3PO4. The developed Ru/A‐H3PO4 catalyst system achieved a complete phenol conversion with cyclohexane selectivity higher than 99 %, making it by far one of the most efficient systems for phenol hydrodeoxygenation. Mercury poisoning experiments revealed that the in situ generated Ru nanoparticles are true a heterogeneous catalyst for hydrogenation. The catalytic activity of metal site for phenol hydrodeoxygenation to cyclohexane decreased with the order of Ru&gt;Rh&gt;Pt≫Pd. Our findings also demonstrated the delicate balance between activity and stability of ionic liquid‐like copolymer‐stabilized nanocatalysts. The research highlights an efficient catalyst system of transforming phenols into alkanes.

Immobilization of Cobalt Phthalocyanine and Tetrasulfophthalocyanine onto MCM-41 and MCM-48: Effect of Immobilization Method on Catalytic Activity

Cobalt tetrasulfophthalocyanine (CoPcS) was chemically anchored to amine-modified MCM-41 and MCM-48 surface. These mesoporous silica were prepared by hydrothermal procedure. Physical mixtures of CoPc in MCM-41 and in MCM-48 were also prepared for comparison purposes. The four prepared catalysts, 10 wt.% CoPcS/NH2-MCM-41, 10 wt.% CoPcS/NH2-MCM-48, 10 wt.% CoPc/MCM-41 and 10 wt.% CoPc/MCM-48, were characterized by X-ray diffractometry (XRD), diffuse reflectance UV-Vis spectroscopy and BET specific surface analysis. The catalytic activity of the immobilized catalysts was tested in the aerobic epoxidation of cyclohexene. CoPcS/NH2-MCM-41 and CoPcS/NH2-MCM-48 showed relatively high epoxide selectivity but low conversion of cyclohexene compared to CoPc/MCM-41 and CoPc/MCM-48. No leaching of metallophthalocyanine from the catalysts immobilized by chemical bonding into the reaction medium was observed and these catalysts could be reused four times.