Benzene Hydrogenation Reaction Research Articles

Reversible hydrogenation and dehydrogenation of benzene for hydrogen storage on highly dispersed Pd/γ-Al2O3 catalyst

The research and development of efficient catalyst is the key to achieving high-capacity hydrogen storage in liquid organic hydrogen carriers (LOHCs). The highly dispersed Pd/γ-Al2O3 catalysts with few-atom Pd were prepared by impregnation method using HNO3 as promoter. The hydrogen storage capacity of the benzene/cyclohexane hydrogen carriers was further investigated by vapor phase benzene hydrogenation and cyclohexane dehydrogenation reactions over the studied Pd/γ-Al2O3 catalysts. The results showed that the metal Pd was the active centers for the benzene hydrogenation/cyclohexane dehydrogenation reactions. The addition of HNO3 can effectively promote the metal Pd to be highly dispersed, thus improving the Pd atoms utilization and reducing the Pd dosage. Meanwhile, the strongly electronic effects between the highly dispersed Pd species and the Al2O3 support promoted the electron-deficient Pdδ+ sites to be formed, which enhanced the adsorption and activation ability for the reactants molecules. The benzene conversion on the Pd/γ-Al2O3 catalyst with a metallic Pd loading of 1.0 wt% reached 97.51 % at 200 °C. While the cyclohexane conversion reached 90.94 % at 400 °C with the actual hydrogen storage capacity of 6.54 wt%, which provided an effective idea for large-scale storage and transportation of H2 based on LOHCs.

THE SCIENTIFIC BASIS OF INDUSTRIAL APPLICATION OF THE PROCESS OF SELECTIVE HYDROGENATION OF BENZENE IN DIFFERENT CATALYTIC SYSTEMS

Pollution of the environment with substances obtained in the production of oil and other products in various industries forces us to take measures to solve environmental problems that have become relevant in recent years. Arenes, belonging to the class of petroleum-derived aromatic hydrocarbons, are very life-threatening substances due to their carcinogenic effects. In this regard, one of the important issues is the release of benzene, a special representative of arenes, from its carcinogenic effect as a toxic and volatile compound, and its use in the production of cyclohexane, which is the main raw material for the production of caprolactam and nylon. The selectivity of the hydrogenation of benzene and the high yield of cyclohexane, the target product, depend on the reaction conditions and the choice of catalysts. In recent years, the application of polymer and zeolite nanocomposite catalysts, as well as modified metal polymer-based catalysts, in obtaining highly active and selective catalysts for the purpose of effective implementation of aromatic hydrocarbon hydrogenation processes is of great interest. Thus, naphthenic hydrocarbons are considered the main starting materials for the synthesis of various classes of compounds. Derivatives of these compounds are used in the pharmaceutical industry as special-purpose caprolactam, adipic acid, cyclohexanone, as a solvent for essential oils, varnishes, paints, as an extractant, etc. are used in synthesis. As a result of investigating the catalytic properties of polymer-mineral catalysts in the benzene hydrogenation reaction, it was determined that these reactions show selectivity in the direction of cyclohexane formation in narrow-pore zeolites (mordenite, clinoptilolite)In the presented work, the main information was collected by analyzing the literature on the work carried out in this direction

Synthesis of PtRe electrocatalysts supported on mesoporous carbon for the ethanol oxidation reaction

Mesoporous carbon was synthesized to be employed as support in PtRe anodic electrocatalysts. The catalysts were prepared by the polyol method with the following Re loadings: 1, 3, 5, and 10 wt.%. The N2 adsorption-desorption isotherms, thermogravimetric measurements, temperature programmed desorption and temperature programmed reduction of the support were performed and the catalysts were structurally characterized by temperature programmed reduction, H2 chemisorption, X-ray diffraction, X-ray photoelectron spectroscopy, benzene hydrogenation reaction, and transmission electron microscopy. Furthermore, the electrochemical characterization of the catalysts was carried out by cyclic voltammetry, chronoamperometry, and CO stripping techniques. The addition of Re leads to a decrease in the CO oxidation onset potential value. The PtRe(3)/MC catalyst exhibited the best electrocatalytic activity, showing an electrochemical active surface area value of 82.5 m2 gPt−1. Moreover, the potential and anodic current values for ethanol oxidation reaction were 889 mV vs Ag/AgCl and 648 mA mgPt−1, respectively. This result is consistent with electronic effects and the smallest particle size found for this catalyst.

Novel Reaction-Adsorption Method for Preparation of Ru–Zn–La/ZrO2 Catalysts with High Catalytic Performance for Selective Hydrogenation of Benzene

A novel wet-chemistry reaction-adsorption strategy via the facile acid–base interaction under mild conditions is demonstrated to fabricate the state-of-the-art Ru–Zn–La/ZrO2 catalysts for selective hydrogenation of benzene to cyclohexene. The catalyst preparation process is systematically investigated and verified with the combination of various characterization techniques. Preloading of lanthanide salts and alkali treatment after calcination not only favor the introduction of ruthenium and zinc species in the later stages but also help enhance the dispersion of the catalysts. The reaction rate constants (k1 and k2) decrease with the increment of the Zn/Ru molar ratio, and the selectivity at 40% conversion (S40) is positively correlated with the k1/k2 ratio, demonstrating the role of Zn species in retarding the hydrogenation activity of Ru and improvement of the selectivity to cyclohexene. In general, the catalytic behavior is dependent on the particle size of Ru, the La-to-Ru electron transfer effect, the content of Zn species, and the surface hydrophilicity of catalyst. These factors are generated by using different precursors and various predesigned La/Ru molar ratios in the preparation recipe. Moreover, a passivation treatment before the hydrogenation reaction can promote the cyclohexene selectivity of the catalyst Ru–Zn–La/ZrO2 (1.6 La/Ru) to 80.6% at a benzene conversion of 43.7%, which meets the industrial requirement. Notably, the specific activity of the catalyst is as high as 1224 gBZ·gRu–1·h–1, over 10 times higher than the industrial criterion. This work provides new insights into the design of Ru-based catalysts for benzene hydrogenation and other hydrogenation reactions as well.

Study of catalytic hydrogenation performance for the Pd/CeO2 catalysts

Abstract Pd/CeO2 catalysts with different metallic Pd loading were synthesized by impregnation method. The physicochemical properties of prepared Pd/CeO2 catalysts and corresponding precursors were studied by XRD, XPS, H2-TPD and H2-TPR. Moreover, the catalytic performance of the Pd/CeO2 catalysts was investigated via gas phase benzene hydrogenation reaction at the temperature of 100–200 °C under atmosphere pressure. Results show that the catalytic performance of prepared Pd/CeO2 catalysts is directly related to the metallic Pd content. The amounts of active metallic Pd and adsorbed-desorbed hydrogen species on Pd/CeO2 catalysts increase with the increasing metallic Pd loading from 1.0 to 3.0%, while the numbers of them are slightly reduced on Pd/CeO2(3.5) catalyst. Furthermore, metallic Pd is highly dispersed on the nano-CeO2 supports, therefore, the prepared Pd/CeO2 catalysts present good gas phase benzene catalytic hydrogenation performance. At 200 °C, the benzene conversion over the Pd/CeO2 catalysts with different metallic Pd loading follows the rule: Pd/CeO2(3.0) > Pd/CeO2(3.5) > Pd/CeO2(2.5) > Pd/CeO2(2.0) > Pd/CeO2(1.5) > Pd/CeO2(1.0), corresponding values are 94.3, 96.4, 89.9, 82.8, 72.7, 42.6 and 94.3%. And the cyclohexane selectivity is 100% on all prepared Pd/CeO2 catalysts.

Coordinatively unsaturated aluminum anchored Ru cluster for catalytic hydrogenation of benzene

The design and synthesis of highly dispersed metal catalyst have attracted increasing attention, and it is still challenging to generate stable metal clusters with high metal loadings. Support plays a crucial role in determining particle morphology and dispersion. Herein, we demonstrate a strategy for synthesizing an amorphous alumina with 62% Al3+penta sites (penta-coordinated Al3+) via solution combustion synthesis. It provides sufficient oxygen defects to anchor Ru species. For benzene hydrogenation reaction, the catalyst displays the high TOF (18833 h−1), which is about 2 times higher than that of catalysts supported on commercial alumina. The DFT calculations also confirm that the high catalytic performance is closely correlated with the special configuration of Ru active sites over coordinatively unsaturated alumina. The penta-coordinated Al3+ was also applied to prepare Pd catalyst with high dispersion. This work provides a superior support which possesses abundant Al3+penta sites and affords a possibility for the generation of high and stable dispersion for the preparation of supported metal catalysts.

Deactivation of platinum on chlorinated alumina catalyst in the light naphtha isomerization process

In order to maintain and increase the lifetime of platinum on chlorinated alumina catalyst, its deactivation was investigated in the presence of oxygenated compounds or mercaptans in the light naphtha hydroisomerization process. A high concentration of methanol or dimethyl disulfide (DMDS) in the feed resulted in irreversible and reversible deactivation of the catalyst. The degree of deactivation and activity recovery of the catalysts measured in the light naphtha isomerization and benzene hydrogenation reactions. The experimental results indicated that when the catalyst was deactivated with oxygenated compounds such as methanol, the catalyst activity was lost drastically, and the regeneration treatment was unable to restore the catalyst’s initial activity. However, a full recovery of the catalyst may obtain when deactivation occurred with dimethyl disulfide. It found that oxygenated compounds affect the acidic functional groups, but mercaptans had an important influence on metallic sites of the catalyst.

Role of tin on the electronic properties of Ni/Al2O3 catalyst and its effect over the methane dry reforming reaction

The Sn effect over the catalytic properties of the Ni/Al2O3 was investigated in the dry reforming of methane and benzene hydrogenation. It was found that the Sn amount plays an important role in the catalytic properties of Ni/Al2O3 catalysts. XRD shows that higher Sn amount and reducing conditions leads to the NiSn metal alloy formation on the Ni particles surface, producing a non-active material. Interestingly, a low Sn amount improves the catalytic performance in the DRM reaction by decreasing the coke deposition, while the activity of Ni-Sn/Al2O3 to CC bond hydrogenation of benzene decreased. DFT calculations of adsorption energy and, catalytic benzene hydrogenation reaction point that the Sn addition increases the electronic density of Ni, decreasing the H2 and benzene adsorption affinity. Therefore, Sn is an excellent electronic promoter that can improve the catalytic stability of the Ni/Al2O3 in the DRM by decreasing the occurrence of parallel reaction that leads to carbon deposition.

Influence of the Procedure for Preparing Ruthenium Nanoparticles on the Internal Surface of Aluminosilicate Nanotubes on Their Catalytic Properties in Benzene Hydrogenation in the Presence of Water

The composition, structure, catalytic activity, and stability of ruthenium catalytic systems prepared using natural aluminosilicate nanotubes as a support were studied. The influence of the preparation procedure on the morphology of ruthenium nanoparticles selectively formed inside mesoporous aluminosilicate nanotubes was examined. The activity and stability of catalysts in the model reaction of benzene hydrogenation in the presence of water [V(C6H6) = V(H2O), 80°C, hydrogen pressure 3.0 MPa, reaction time 3 h] were studied. The catalyst containing 1.02 wt % ruthenium, prepared by reduction of the ruthenium ethylenediaminetetraacetate complex in a hydrogen stream at 400°С, exhibits higher activity (the benzene conversion in the 3-h reaction was 100%) and higher stability in the reaction (the benzene conversion after three reaction cycles was 95%) compared to the system with the similar ruthenium content (0.98 wt %) prepared by reduction with a sodium borohydride solution. The reduction with hydrogen leads to the formation of highly stable ruthenium nanoparticles with the mean diameter of 2 nm, tightly bound to the internal surface of aluminosilicate nanotubes.

Nano-Pd/CeO2 catalysts for hydrogen storage by reversible benzene hydrogenation/dehydrogenation reactions

Nano-CeO2 supports, which have different structure from different preparation methods, were used to prepare nano-Pd/CeO2 catalysts. The hydrogen storage capacity of prepared nano-Pd/CeO2 catalysts were studied via vapor phase benzene hydrogenation and cyclohexane dehydrogenation reactions. Results show that the prepared Pd/CeO2 catalysts exhibit excellent benzene hydrogenation and cyclohexane dehydrogenation performances. The catalytic performance of the Pd/CeO2 catalysts is related to the dispersion of metallic Pd, hydrogen adsorption-desorption ability and structure of Pd/CeO2 catalysts and so on. And those properties are also directly affected by the morphology and mesoporous structure of the prepared nano-Pd/CeO2 catalysts that can be regulated by CeO2 support preparation methods. The synergistic effect between metal Pd, CeO2 support and their structures can effectively promote benzene hydrogenation and cyclohexane dehydrogenation, thus promoting hydrogen storage capacity. The prepared Pd/CeO2-HT catalyst, which has high specific surface area, developed pore structure and highly dispersed metal Pd species, exhibits superior catalytic performances. And, the Pd/CeO2-HT catalyst exhibits superior catalytic hydrogen storage performances. The benzene conversion over it at 200 °C reaches 99.5%. Whereas the cyclohexane conversion at 450 °C is 65.3%, and the H2 production capacity is 73.77 g/h.

PROCESS SIMULATION AND OPTIMIZATION OF CYCLOHEXANE MANUFACTURING PLANT USING UniSim AND HINT

The Energy crisis and Low production rate are the important parameters in industrial operations. In this point, the simulation and optimisation of plant is highly desirable. This study shows the simulation of cyclohexane manufacturing plant. Cyclohexane is mainly used as an intermediate chemical compound for the production of adipic acid. It prepared by the hydrogenation reaction of benzene at elevated temperature and pressure. Honeywell’s UniSim software R470 was used for the simulation and optimization processes and the fluid package employed was PRSV. Heat exchanger network design for pinch method has been carried out using HINT educational software. Pinch technology is used for Energy and Cost optimisation. This study reveals with all the stages of the design, which include cost targeting, area targeting, utility selection and heat exchanger network designing (HEN). The results of the base and optimized cases were compared and analysed. It has been shown that the developed UniSim model of this work can be used to represent, simulate and optimize a cyclohexane stabilization system successfully. This simulation helps engineers to create steady-state plant design, performance monitoring and troubleshooting.

Hydrogenation of benzene and toluene over supported rhodium and rhodium-gold catalysts

Rhodium and rhodium-gold catalysts supported on amorphous aluminosilicates (ASA), titanium dioxide (rutile, TiO2) was prepared in two different ways: absorption and colloidal method. The catalysts were characterized by an inductively coupled plasma optical emission spectrometer (ICP-OES), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The activity and selectivity of the prepared catalysts were tested by the hydrogenation of benzene and toluene. Hydrogenation was conducted at a pressure of 4 MPa and a temperature 80 °C. The bimetallic Rh-Au/ASA catalyst prepared by the absorption method showed higher activity and selectivity in benzene hydrogenation reaction, the same catalyst prepared by the colloidal method demonstrated lower selectivity.

The Influence of Ruthenium Nanoparticle Size on the Activity of Benzene Hydrogenation Catalysts

Ruthenium nanoparticles of varying sizes were synthesized under microwave radiation and deposited on natural aluminosilicate nanotubes. The catalytic properties of the materials obtained in the hydrogenation reaction of benzene were studied, and the influence of ruthenium nanoparticle size effect on the activity of the synthesized catalysts was determined. Conversions, activation energies, turn-over frequency, and rate constants of reactions were defined.

Rhodium nanoparticles supported on covalent triazine-based frameworks as re-usable catalyst for benzene hydrogenation and hydrogen evolution reaction

Rh@CTF-1 nanomaterial is a highly active (TOF ∼ 31 000 h−1) heterogeneous catalyst for the efficient hydrogenation of benzene under mild and solvent-free conditions.

Effect of number and properties of specific sites on alumina surfaces for Pt-Al2O3 catalysts

In this work, how the number and properties of specific sites on alumina surfaces affect the specific interaction between Pt and alumina was investigated by using X-ray diffraction, ethanol temperature programmed desorption, diffuse reflectance infrared Fourier transform spectroscopy, H2 chemisorption, scanning transmission electron microscopy and benzene hydrogenation reaction. Here, we chose two sets of model aluminas having different number of sites with the identical properties and different properties of sites with the same number based on ethanol TPD. The H2 chemisorption results for the model aluminas show that H/Pt are all similar for low Pt loadings, but significantly different for high Pt loadings. For 1 wt% Pt/Al2O3, the number of specific sites on all the aluminas was sufficient to disperse all the Pt, leading to only highly dispersed Pt clusters (∼1 nm). However, at 10 wt% Pt/Al2O3, the number of Pt atoms is greater than that of the specific sites on the alumina surface, resulting in a bimodal distribution of large agglomerated Pt (>10 nm) and highly dispersed Pt clusters (<3 nm) revealed by XRD and TEM. Overall, the results clearly demonstrated that Pt shows higher dispersion with increasing number of sites and interaction strength, because the Pt atoms can interact with specific sites on alumina in greater numbers and more strongly. However, these Pt dispersion changes do not represent the gradual change in Pt cluster sizes, but the relative population change of small (<3 nm) and large agglomerated Pt clusters (>10 nm) under bimodal distribution. The number of large agglomerated Pt clusters decreased with increasing number of sites and interaction strength. This fundamental understanding provides an important perspective for designing Al2O3-based supported catalysts.

Coordinatively Unsaturated Al3+ Sites Anchored Subnanometric Ruthenium Catalyst for Hydrogenation of Aromatics

Single metal atoms and metal clusters have attracted much attention because of their high dispersity, special electronic structures, and uniformity of active sites as heterogeneous catalysts, but it is still challenging to generate stable single atoms and clusters with high metal loadings. Supports play a crucial role in determining particle morphology and maintaining dispersion. Herein we synthesize an amorphous alumina with 29% coordinatively unsaturated pentacoordinate Al3+ (Al3+penta) sites, which can anchor atomically dispersed Ru species with 1 wt % loading. Strong interactions between Ru and Al3+penta centers were detected, resulting in distinct Ru geometric and electronic features. When used in benzene hydrogenation reaction, fairly high specific activity (TOF = 5180 h–1) were obtained. The high catalytic performance is considered closely correlated with the high utilization of special Ru active sites.

Ni‐W Catalysts Supported on HZSM‐5/HMS for the Hydrogenation Reaction of Aromatic Compounds: Effect of Ni/W Ratio on Activity, Stability, and Kinetics

ABSTRACTNi‐W/HZSM5‐HMS catalysts were evaluated for the benzene hydrogenation reaction at 130–190°C. To study the catalyst characterization, X‐ray diffraction, X‐ray fluorescence, Fourier transform infrared, UV–vis, diffuse reflectance spectra, temperature‐programmed desorption of NH3, FT‐IR of adsorbed pyridine measurements (Py‐IR), H2 chemisorption, nitrogen adsorption–desorption, and TGA techniques were used. Kinetics of benzene hydrogenation was investigated under various hydrogen and benzene pressures, and the effect of reaction conditions on catalytic performance was studied. The results showed that bimetallic catalysts have better ability than a monometallic catalyst (Ni/HZSM5‐HMS) for this reaction, such as maximum benzene conversion (100%), minimum toluene conversion (1.76–40%), very low converted xylene, benzene selectivity (100%), good catalytic stability against coke deposition, and appropriate kinetic parameters.

Synthesis of Ru/CoNi crystals with different morphologies for catalytic hydrogenation

Cobalt–nickel alloy crystals with different morphologies, such as flower-like, column-like, mushroom-like and dendrite-like, were prepared by a facile hydrothermal or solvothermal reduction approach without the addition of any surfactant, using hydrazine hydrate as a reducing agent, ethanediamine as a capping agent and a mixture of nickel(II) chloride hexahydrate (NiCl2·6H2O) and cobalt(II) chloride hexahydrate (CoCl2·6H2O) as a precursor. The effect of hydrothermal temperature (120, 150 or 180 °C) and solvent (water or ethanol) on the shape of the CoNi crystals was investigated in this work. The corresponding Ru/CoNi catalysts (Ru-on-CoNi nanocrystals) were obtained via a galvanic replacement reaction. The sizes, element chemical states, morphologies and structures of the CoNi and Ru/CoNi samples were characterized by X-ray diffraction (XRD), scanning electronic microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and high-sensitivity low-energy ion scattering (HS-LEIS) techniques. The catalytic performance of the as-synthesized catalysts was evaluated by using the benzene hydrogenation reaction. The Ru/CoNi catalyst with a dendrite-like morphology exhibited the highest catalytic hydrogenation activity among the Ru/CoNi catalysts with different shapes. This was mainly due to its high Ru dispersion, many defect sites and positive synergistic effect compared with ruthenium, nickel and cobalt related species. Importantly, the cost of recycling the Ru/CoNi catalysts was relatively low because they could be recycled by magnetic separation.

Effect of the Preparation Method on the Electrocatalytic Activity of Pt-Sn/Nanotubes Catalysts Used in DMFC

A series of bimetallic Pt-Sn catalysts supported on multiwalled carbon nanotubes (NT) for methanol oxidation reaction was prepared by different methods that involve ethylene glycol synthesis under reflux conditions and sodium borohydride reduction (using water or ethylene glycol as solvents) at 55°C. Pt-Sn/NT catalysts containing 20 wt% platinum with Pt:Sn atomic ratios of 5:1, 3:1 and 1:1 were prepared and their morphology and electrocatalytic activities were characterized by temperature programmed reduction, X-ray photoelectron spectroscopy, H2 chemisorption, benzene hydrogenation reaction, transmission electron microscopy, cyclic voltammetry, linear sweep voltammetry, chronoamperometry and CO stripping. The electrocatalysts performance depends strongly on the preparation method and Pt:Sn atomic ratios, with the Pt3Sn1/NT sample prepared by ethylene glycol displaying the highest activity for methanol electrooxidation, a good CO tolerance and an important stability.

Density-functional-based tight-binding parameterization of Mo, C, H, O and Si for studying hydrogenation reactions on molybdenum carbide

Hydrogenation reactions catalyzed by transition-metal-containing nanoparticles represent an important type of reaction in chemical industry. However, the modeling of these reactions in their working conditions requires much longer simulation times than what could usually be achieved with ab initio or first-principle methods. To address this problem, in this work, the density-functional-based tight-binding (DFTB) method was parameterized for hydrogenation reactions on molybdenum carbide catalysts, involving the elements C, H, Mo, O and Si. The overall quality of the DFTB parameters was tested with band structure/molecular orbital energies, molecular/crystal structures, chemisorption bond strengths, hydrogen adsorption energies, hydrogenation reaction energies, molecular vibrational frequencies, energy barriers and the structures of the transition states for systems of interest. The parameterized DFTB method gave errors of <1.45 % for bond distances of hydrocarbons and 4.86 % for non-hydrocarbons. It could reproduce the structure and vibrational frequencies (with errors of about 100 cm−1) of selected hydrocarbon–molybdenum carbide complexes obtained from DFT calculations. Good agreement was reached between DFTB and DFT on the dissociative adsorption of hydrogen on the α-Mo2C (0001) surface. For most of the hydrogenation reactions examined, DFTB showed errors of ~2 kcal/mol compared to DFT/PBE, with a few exceptions of ~5 kcal/mol. It could also describe the reaction energies, the forward and reverse energy barriers and the transition-state structures for the benzene hydrogenation reaction on a Mo38C19 cluster.