Cyclohexene Selectivity Research Articles

Hydrodeoxygenation of lignin-derived phenolic compounds into aromatic hydrocarbons under low hydrogen pressure using molybdenum oxide as catalyst

MoO3 catalyst was prepared by calcination using (NH4)6Mo7O24·4H2O as precursor and was characterized by XRD, XPS, H2-TPR and low temperature N2 adsorption. Hydrodeoxygenation of phenol was conducted to investigate the catalytic performance of MoO3 catalyst at lower H2 pressure. Effects of reaction temperature, reaction time and N2 partial pressure on the phenol conversion and product distribution were tested carefully. MoO3 catalyst was found to preferentially produce arenes with high selectivity, while at lengthened reaction time cyclohexane selectivity was increased gradually. Oxygen vacancy site of MoO3 (Mo5+) was deemed to be the active center in the hydrodeoxygenation of phenol, which accounts for the cleavage of CAR-OH to benzene. In addition, MoO3 catalyzed HDO reactions were further tested using different phenolic compounds as reactants. Experimental results suggest MoO3 catalyst can be widely applied in the conversion of diverse lignin-derived phenolic compounds conversion to aromatic hydrocarbons.

Highly effective methylated Ti MCM-41 catalyst for cyclohexene oxidation

A series of Ti containing MCM-41 materials were synthesized with different Si/Ti molar ratios and tested for cyclohexene epoxidation reaction. TiMCM-41 with Si/Ti ratio 40 which gave maximum conversion and selectivity to epoxide was methylated with methyltriethoxysilane (MTES) in this reaction. Accordingly, four different methyl loading (5, 10, 15 and 20 mol % of MTES w.r.t. TEOS) TiMCM-41(Si/Ti 40) samples were prepared. The materials were characterized by different physical techniques such as PXRD, FT-IR spectroscopy, UV–vis DRS spectroscopy, N2 adsorption-desorption isotherm, SEM-EDX, TEM, TGA and ICP-OES. The catalysts were then tested for cyclohexene epoxidation reaction in the presence of H2O2 avoiding TBHP. The conversion and selectivity for cyclohexene obtained with 10MeTiM-1 (Si/Ti 40) were found to be the best not only among the catalysts investigated in the present work, but also among all the catalysts studied so far for the reaction.

Selective Hydrogenation of Benzene to Cyclohexene over Ru-Zn Catalysts: Mechanism Investigation on NaOH as a Reaction Additive

Ru-Zn catalysts were synthesized via a precipitation method, and the mechanism of NaOH modifying Ru-Zn catalysts on the selective hydrogenation of benzene to cyclohexene was thoroughly investigated. Fresh as well as used catalysts were characterized via X-ray diffraction (XRD), X-ray Fluorescence (XRF), transmission electron microscope (TEM), scanning electron microscope (SEM), Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT), respectively. Before catalytic experiments, metallic Ru and rodlike ZnO were detected from fresh Ru-Zn catalysts. Notably, with the increasing concentration of NaOH added into the reaction medium (e.g., from 0 to 0.6 mol·L−1), the dispersion of ZnO on the Ru surface significantly improved, resulting in the enhancement Ruδ+ species of electron deficiency. The catalytic activity towards benzene conversion was therefore retarded and the selectivity towards cyclohexene was improved. When the added NaOH concentration reached 0.6 mol·L−1, the atomic ratio of Zn/Ru decreased from 0.27 (when no NaOH was added) to 0.16, benzene conversion of 45.3%, and cyclohexene selectivity of 89.3% was achieved using a batch reactor after 25 min of reaction time. However, with continually increasing the NaOH concentration, i.e., to 1.2 mol·L−1, parts of ZnO could react with the over-added NaOH, leading to the unfavorable consumption of uniformly dispersed ZnO. This causes the increasing of catalytic activity towards benzene conversion, as well as the decreasing of the selectivity towards cyclohexene. Moreover, no loss of catalytic activity and selectivity towards cyclohexene formation from selective hydrogenation of benzene was observed after 10 times of catalytic experiments without any regeneration.

Partial Hydrogenation of Benzene to Cyclohexene on Ru@XO2 (X = Ti, Zr, or Si)

The effect of coating Ru particles with a film of hydrophilic materials on the tetra-phase partial hydrogenation of benzene to cyclohexene was examined. By the sol–gel method, amorphous mesoporous TiO2, ZrO2, and SiO2 were coated on hexagonal Ru particles, by which Ru@XO2 (X = Ti, Zr or Si) catalysts were prepared. During the partial hydrogenation of benzene on Ru@XO2, the diffusion of benzene and cyclohexene dissolved in the water phase onto Ru particles is suppressed by the presence of mesoporous coating film. The diffusion of benzene is retarded further by the hydrogen bonding with the structural OH groups contained in hydrophilic materials. Because of the delicate diffusion behavior of benzene and cyclohexene through coating film, a decreasing rate of benzene conversion but a significantly increasing cyclohexene selectivity was observed in the partial hydrogenation on different Ru@XO2 catalysts. A maximum cyclohexene yield of 52.6 mol % occurs on Ru@TiO2 at the benzene conversion of 85.0%.

Effect of support composition on the structural and catalytic properties of Ru/AlOOH–SiO2catalysts for benzene selective hydrogenation

A volcano-type correlation between the acid amount and cyclohexene selectivity over the Ru/AlOOH–SiO2catalysts was elucidated in benzene selective hydrogenation.

Synthesis of Fe3O4 core/alumina shell nanospheres for partial hydrogenation of benzene

We report a novel synthesis of Fe3O4 core/alumina shell nanosphere composite for partial hydrogenation of benzene. Fe3O4 core/alumina shell (MFeCA) structured nanospheres were obtained by reducing a hematite core/alumina precursor shell (HFeCAP) nanosphere precursor under H2/N2 gas flow. The magnetic alumina nanospheres (MFeCAs) possess not only uniform size (180∼350nm) but also adjusted saturation magnetization value. A novel Ru-based magnetic catalyst was synthesized for the partial hydrogenation of benzene in magnetically stabilized bed (MSB). The performance of magnetic catalyst in MSB demonstrates that it’s an effective and highly selective method for partial hydrogenation of benzene. The chain regime of the MSB reactor’s operation conditions is responsible for the high selectivity of cyclohexene.

Synthesis and Characterization of Oligomeric Ionic Liquid/Heteropoly Acid Composite as a New Heterogeneous Catalyst through Anion-Exchange Method for Selective Cyclohexane Oxidation with Molecular Oxygen under Solvent-Free Conditions

In this work, we investigated solvent-free oxidation of cyclohexane using oligomeric ionic liquid (OIL)/heteropoly acid (HPA) composite with molecular oxygen under solvent-free conditions. OIL has six imidazolium cores which synthesized in three successive stages and was anion-exchanged by phosphomolybdic acid (H3PMo12O40, PMo) to synthesize OIL/HPA composite. OIL and OIL/HPA composite were characterized by different techniques such as, FT-IR, UV, BET, TGA, XRD, FESEM, EDX, and TEM. Optimal reaction conditions were obtained by evaluating the effective parameters on the reaction including temperature, time, oxygen pressure, and amount of the catalyst. The main product of the reaction in the presence of 20 mg of catalyst and 5 mL of cyclohexane was cyclohexanone by 21% conversion and 75% selectivity at 110 °C and 20 bar oxygen pressure after 5 h. The OIL/HPA showed good stability under reaction conditions and maintained its catalytic activity up to five cycles with little decrease in reaction conversion.

Fabrication of Porous MoS2 with Controllable Morphology and Specific Surface Area for Hydrodeoxygenation

SiO2 nanoparticles modified with aminopropyl-triethoxysilane (APTES) were used as hard templates for preparing porous MoS2. The method offers the advantages of simple steps, convenient operation, controllable pore size, and a specific surface area. Two morphologies of MoS2 were obtained by using thiourea and L-cysteine as sulfur sources, respectively. Porous MoS2 prepared by using thiourea had a smooth surface, whereas the surface of porous MoS2 prepared with L-cysteine had many burrs. The MoS2 nanomaterials with the respective morphologies were used to catalyze the hydrodeoxygenation (HDO) reaction. The activity of MoS2 prepared with L-cysteine was lower than that prepared with thiourea. Transmission electron microscopy and X-ray diffraction analyses showed that MoS2 had a large sheet-shaped structure and high crystallinity, leading to high reaction activity and high selectivity for cyclohexane. The reaction temperature also influenced the HDO significantly. The mechanism of hydrogenation of phenol was discussed.

Highly Selective Cyclohexane Oxidation Catalyzed by Ferrocene in Ionic Liquid Medium

Background: Although economically very important in view of the significance of the oxidized products for the manufacture of adipic acid and caprolactam (precursors to polyamides widely used in several industries), the current cyclohexane oxidation industrial process leads to very low conversions (ca. 4%) to assure a reasonable selectivity (ca. 85%). Therefore, there is an urgent need to develop sustainable selective cyclohexane oxidation chemistry, which is the main objective of this work. Keywords: Alkane functionalization, ferrocene, ionic liquid, catalysis, cyclohexane oxidation, water, KA oil

Enhanced Phenol Hydrodeoxygenation Over a Ni Catalyst Supported on a Mixed Mesoporous ZSM-5 Zeolite and Al2O3

Developing highly active catalysts for bio-oil hydrodeoxygenation is of great importance in the low cost production of conventional transport alkane fuels. Toward this goal, a Ni catalyst supported on mesoporous ZSM-5 zeolite mixed with 25 wt% γ-Al2O3 (Ni/Al-HMZSM-5) was designed for hydrodeoxygenation of phenol as model compound. For comparison, the catalytic activities of Ni catalysts on conventional microporous ZSM-5, mesoporous ZSM-5 and γ-Al2O3 were also investigated. It was found that almost complete phenol conversion (99.6%) was achieved over the Ni/Al-HMZSM-5 catalyst along with a high cyclohexane selectivity (98.3%) under a relatively mild condition (170 °C, 4 MPa H2). The open mesopores, stronger acid sites and synergism effect of Bronsted and Lewis acidities are jointly responsible for the excellent hydrodeoxygenation performance. In addition, it was shown that the catalyst was recycled several times with little loss of activity and selectivity.

Enhanced stability of Pd-Ni 2 P/SiO 2 catalysts for phenol hydrodeoxygenation in the presence of H 2 O

Abstract This work compares the stability of Ni 2 P/SiO 2 , Pd/SiO 2 and Pd-Ni 2 P/SiO 2 catalysts during phenol hydrodeoxygenation (HDO) in the presence of H 2 O. The Pd-Ni 2 P/SiO 2 catalyst (PNP) was prepared by an in-situ reduction method in which PdCl 2 is added directly to unpassivated Ni 2 P/SiO 2 . A series of physicochemical characterizations, such as X-Ray diffraction, transmission electron microscopy, thermogravimetry, temperature programmed reduction and X-ray photoelectron spectroscopy were used. The results showed that the PNP catalyst has the highest stability among these catalyts. Phenol conversion and cyclohexane selectivity vary from 100.0% to 93.0% and from 94.2% to 83.1%, respectively with 0.1 g catalyst at 2 MPa and 493 K in four reaction cycles. Enhanced stabiltiy is attributed to Pd highly dispersed and strongly interacting with Ni 2 P on the PNP catalyst, resulting in negligible aggregation and loss of metal as well as very low carbon formation over the PNP catalyst. In contrast, the deactivation of Pd/SiO 2 results from aggregation and loss of Pd, while that of Ni 2 P/SiO 2 is due to the loss of phosphorus, phosphide oxidation and carbon deposition in the presence of H 2 O.

Selective cyclohexane oxidation over vanadium incorporated silica pillared clay catalysts: The effect of VOx content and dispersion

The design of efficient and stable clay based materials for catalytic technologies is a great challenge. We demonstrated a new approach of fabricating vanadium incorporated silica-pillared clay by interlayered self-assembly synthetic route. And such synthetic route utilized tartaric acid as the complexing reagent, both dodecyl dimethyl benzyl ammonium bromide and octadecylamine as the mixed structure-directing agent. The obtained vanadium-containned silica-pillared clay samples were characterized by X-ray fluorescence, X-ray diffraction, transmission electron microscopy, N2 adsorption-desorption isotherms, Fourier-transform infrared spectroscopy, diffuse reflectance ultraviolet–visible spectroscopy and X-ray photoelectron spectroscopy techniques. Characterization results indicate that there is an important correlation between the concentration of octadecylamine and uniform structure of the obtained vanadium-containned sample. The octadecylamine is not only used as swelling agency but also decreases the polarity to confirm the uniform mesoporous structure form in the interlayered regions. It was generally considered that hydrothermal synthesis bears the advantage of incorporating active metal ions into the framework in the tetrahedral coordination with V4+ state under the combined action of complexing reagent and mixed structure-directing agent. And the V2O5 phase was gradually formed via aggregation and agglomeration of increasing highly dispersed vanadium species. The catalytic behaviour and performance was examined using the selective oxidation of cyclohexane. The obtained catalyst possesses larger surface area and mesoporous volume and uniform slit-shaped mesopores, which are beneficial to the diffusion of the vanadium atom and responsible for higher yield of the KA oil. And the mechanism associated with the porous structure change has also been discussed.

Bimetallic Cu-Ni catalysts supported on MCM-41 and Ti-MCM-41 porous materials for hydrodeoxygenation of lignin model compound into transportation fuels

The design of novel, efficient supported bimetallic catalysts for the transformation of renewable lignin model compounds into valuable products is currently an emerging research topic. This study investigates the synthesis, characterization and the catalytic application of bimetallic Cu-Ni catalysts supported on pure MCM-41 and Ti incorporated MCM-41 porous materials for the valorization of a lignin model compound (i.e. guaiacol) into the transportation fuels via hydrodeoxygenation route (HDO). The investigated characterization results revealed that the Ti species are well-dispersed within the MCM-41 framework by a tetrahedral coordination. NH3-TPD studies show that the incorporation of Ti into the MCM-41 framework generates large amounts of acidic sites. It was also found that, the coordinated Ti species enhance the dispersion of CuO and NiO species on the surface of Ti-MCM-41 support. The CuNi/Ti-MCM-41 catalyst shows excellent reducible properties due to the co-operative effects of CuO and NiO with the Ti-MCM-41 support. The catalytic experiments revealed that the CuNi/Ti-MCM-41 catalyst exhibits a higher guaiacol conversion (~90.49%) and superior selectivity to cyclohexane (~50.09%) than the CuNi/MCM-41 catalyst which exhibits only ~10.57% cyclohexane selectivity with a guaiacol conversion of ~37.03%. The guaiacol conversion and cyclohexane selectivity were found to increase with the increase of reaction pressure from 40 to 100bar for CuNi/Ti-MCM-41 catalyst. It has been demonstrated that the HDO of guaiacol proceeds via demethoxylation (CAR-OCH3 cleavage) over the CuNi/Ti-MCM-41 catalyst and both demethylation (CARO-CH3 cleavage) and demethoxylation (CAR-OCH3 cleavage) pathways are possible over the CuNi/MCM-41 catalyst in HDO of guaiacol.

Effect of Ti loading on structure-activity properties of Cu-Ni/Ti-MCM-41 catalysts in hydrodeoxygenation of guaiacol

Various Cu-Ni/Ti-MCM-41 catalysts by varying Ti amount (Ti/Si=10, 20 and 30%) were synthesized for hydrodeoxygenation of guaiacol and characterized by XRD, N2 adsorption-desorption, NH3-TPD, H2-TPR and Raman spectroscopy. The Ti loading shows an adverse effect on the catalyst surface area. But, more number of acidic sites (5173.55μmol/g) were found for 20% Ti loaded Cu-Ni/Ti-MCM-41 catalyst. The 20% Ti loaded Cu-Ni/Ti-MCM-41 catalyst shows a high guaiacol conversion (74.2%) and cyclohexane selectivity (48.81%) which is due to abundant acid and redox sites: acid sites initiate removal of oxygen via dehydration, while hydrogenation of guaiacol to cyclohexane is promoted by redox sites.

Synergistic effects of highly active Ni and acid site on the hydrodeoxygenation of syringol

The hydrodeoxygenation of syringol was explored with novel step by step precipitated Ni/SiO2-Al2O3 catalyst under mild conditions. Demethoxylation and dehydroxylation occurred in the first step, followed by the hydrogenation of benzene. Cyclohexane was formed eventually. Ni/SiO2-Al2O3 catalyst possessed high nickel dispersion and high amounts of acid sites. The synergistic effects of highly active Ni and acid site were the key to realize the occurrence of deoxygenation. These specialties resulted in the complete conversion of syringol at 200°C, with the cyclohexane selectivity up to 97.8%, much better than the hydrodeoxygenation performances of single Ni/SiO2 and Ni/Al2O3.

Fe oxide nanoparticles/Ti-modified mesoporous silica as a photo-catalyst for efficient and selective cyclohexane conversion with O2 and solar light

Photocatalytic partial oxidation of cyclohexane with O2 and solar light by mesoporous silica with grafted Ti coupled to Fe oxide nanoparticles.

Control of model catalytic conversion reaction over Pt nanoparticle supported mesoporous BEA zeolite catalysts

Nanocrystalline mesoporous BEA zeolites supporting Pt metal nanoparticles have been investigated for the control of model catalytic reaction using methylcyclopentane as the reactant, while controlling the aluminum content in zeolite, Pt loading, Pt size and reaction temperature. Four different mesoporous BEA zeolites with different aluminum content were prepared via post-synthetic dealumination process with aqueous HCl solution. Pure mesoporous BEA zeolites without Pt metal nanoparticles converted methylcyclopentane to acyclic isomers via ring-opening and dehydrogenated version of methylcyclopentane as the major products, whereas Pt metal nanoparticle supported counterparts produced C6-cyclic products (cyclohexane, benzene) most dominantly. In the case of Pt loading, the cyclohexane/benzene formation ratio decreased as the loading of Pt metal nanoparticle increased. As the Pt size increased from 2.5 to 5, 7nm, cyclohexane selectivity decreased whereas benzene selectivity increased. However, their tendencies were not significant, which means that the size of Pt nanoparticle is not crucial for control of product selectivity. As the reaction temperature increased from 150 to 200, 250°C, cracking reaction pathway became much significant at the expense of that other reaction pathways were alleviated. This was due to the strong acidity of the mesoporous BEA zeolite support, which could be resolved by supporting Pt metal nanoparticles on weakly acidic mesoporous support such as aluminum-incorporated mesoporous silica.

Selective cyclohexane oxidation catalyzed by manganese porphyrins and co-catalysts

Several polar molecules, such as alcohols, ketones, esters and acids, were used as co-catalysts for the cyclohexane oxidation catalyzed by manganese porphyrins, and the catalytic activity was found to be closely related to polarity of co-catalysts. The results indicated that the total selectivity of products was as high as 96.3% and glutaric acid selectivity was up to 50.9%. Thus, the proposed method provides a new approach for preparing glutaric acid.

Effect of microwave calcination on catalytic properties of Pt/MgAl(Sn)Ox catalyst in cyclohexane dehydrogenation to cyclohexene

This paper describes an investigation on catalytic properties of Pt nanoparticles supported on MgAl(Sn)Ox mixed oxide for cyclohexane dehydrogenation to cyclohexene. The MgAl(Sn)Ox supports were synthesized by microwave calcined hydrotalcite-derived precursors, and Pt/MgAl(Sn)Ox catalysts were prepared by an incipient wetness impregnation method. The catalysts were characterized by X-ray diffraction (XRD), hydrogen temperature-programmed reduction (H2-TPR), hydrogen temperature-programmed desorption (H2-TPD), X-Ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The results showed that the microwave calcination changed the interfacial character between Pt and support, and strengthened the interaction between tin and support, and facilitated the high dispersion of Pt nanoparticles presented on the support. These effects resulted in higher activity, stability and cyclohexene selectivity in cyclohexane dehydrogenation to cyclohexene.

A facile and low-cost synthesis of MoS2 for hydrodeoxygenation of phenol

MoS2, Ni-doped MoS2, and Ni-doped MoS2/Al2O3 were synthesized by using thiourea as an organosulfur source with simple and low cost methodology to convert phenol, a model compound of lignin biomass into cyclohexane via catalytic hydrodeoxygenation (HDO). As-synthesized catalysts were characterized by X-ray diffraction, thermal gravimetric analysis, N2 sorption, transmission electron microscopy, and X-ray absorption near-edge structure. The phenol conversion was achieved better in semi-amorphous MoS2 than the crystalline one. In addition, all developed MoS2 showed high selectivity toward HDO of phenol than hydrogenation of phenol, leading to ~90% of cyclohexane selectivity in Ni-doped MoS2.