Dehydrogenation Of Cyclohexane Research Articles

Toward the improvement in unsaturated alcohol selectivity during α,β-unsaturated aldehyde selective hydrogenation, using Zn as promoter of Pt

Pt/SBA-15 catalysts, modified by zinc addition (at different Zn/Pt atomic ratios) via the co-impregnation method, were tested for the liquid phase hydrogenation of citral. The influence of the Zn insertion on the Pt monometallic catalyst properties was evaluated by different physico-chemical techniques, including X-ray diffraction, N2-physisorption, transmission electron microscopy, hydrogen chemisorption, and cyclohexane dehydrogenation as model reaction for platinum accessibility and zinc covering evaluation. On the catalysts, the hexagonal periodic structure of SBA-15 framework was maintained indicating that neither Pt and Zn impregnations, nor thermal treatments affect the organized structure of the support. A decrease of the platinum metallic accessibility was observed with the increase in the Zn concentration in the materials, which was explained, on the basis of the TEM analysis, by a poisoning of the platinum accessible sites by zinc species. For the citral hydrogenation, Pt/SBA-15 monometallic catalyst is very active, with 100% conversion obtained after 30min reaction time, but very poorly selective in unsaturated alcohols. Zinc addition led to an inhibition of the hydrogenating activity, in agreement with the decrease of the active surface, but contributed to an increase in the selectivity to unsaturated alcohols. Selectivity in unsaturated alcohol was observed to reach a maximum of 75%, for a Zn content equal to 0.3wt.%, that is a very interesting value if compared to performances obtained with other more classical dopant including titania and germanium.

Selection of Active Modified Zeolite Catalyst and Kinetics of the Reaction of Selective Oxidative Dehydrogenation of Cyclohexane to Cyclohexadiene 1,3

The catalytic activity of the modified zeolites in the reaction of selective oxidative dehydrogenation of cyclohexane to cyclohexadiene-1,3 has been investigated. It has been found that, the catalyst, Cu Zn Co Cr-clinoptilolite (Cu2+—0.5%; Zn2+—0.2%; Co2+—0.1%; Cr3+—0.1%) shows the most activity in this reaction. A kinetic scheme of the mechanism of the reaction has been suggested and on the basis of this scheme, kinetic model of the process has been developed. Numerical values of the kinetic parameters were calculated.

Production of Hydrogen, Methanol and Benzene Simultaneously in an Industrial Scale Reactor by Considering Effect of Flow Type Regimes

In this study, exothermic reaction of methanol synthesis is coupled with endothermic reaction of dehydrogenation of cyclohexane in a two-packed bed reactor in order to simultaneous production of hydrogen, methanol and benzene. Steady-state, heterogeneous model predicts the performance of this configuration. The simulation results for co-current and counter-current modes in thermally coupled methanol reactor (TCMR) are investigated and compared with data of an industrial scale conventional methanol reactor (CMR) with same feed conditions. In addition, the variation of different operating parameters along the reactor has been considered. The simulation results represent 1.89 % enhancements in methanol recovery yield of co-current mode in TCMR in comparison with CMR. Also, results show that hydrogen recovery yield in dehydrogenation of cyclohexane side in co-current and counter-current modes of TCMR is equal to 2.352 and 2.255, respectively. Finally, TCMR in co-current mode is a feasible reactor for cost reduction because it has benefits such as production of multiple products, enhancement of productivity by shifting equilibrium of reactions to forward, large savings in the operational and capital costs, compact and efficient process.

Catalytic performance of Mo2C supported on onion-like carbon for dehydrogenation of cyclohexane

Mo2C is a promising substitute for noble metal catalysts. Mo2C unsupported and supported on carbon (Mo2C/C) including activated carbon (AC) and onion-like carbon (OLC) was used for hydrogen production. The activity and stability of the Mo2C based catalysts in the dehydrogenation of cyclohexane were studied. The onion-like carbon supported Mo2C catalyst (Mo2C/OLC) was characterized by XRD, TEM and EDS techniques. The results indicate that the Mo2C/OLC catalyst exhibited high stability and activity by adjusting the Mo contents compared to other catalysts. The structures and morphologies of OLC as well as the dispersion of Mo2C did not change before and after reaction of the Mo2C with 15 wt% Mo, which suggests that onion-like carbon is an effective support and Mo2C/OLC is a potential catalyst substitute for noble metals in dehydrogenation.

Size-controlled synthesis of monodisperse nickel nanoparticles and investigation of their magnetic and catalytic properties

Monodisperse nickel nanoparticles (NPs) with different size were synthesized via the thermal decomposition approach using nickel acetylacetonate as precursors and trioctylphosphine as surfactant in oleylamine. The structure and morphology of as-synthesized nickel NPs were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM) and selected area electron diffraction (SAED). The surface states of as-synthesized nickel NPs were characterized by Fourier transform infrared (FT-IR) spectra. The textural properties of as-synthesized nickel NPs were characterized by N2 adsorption–desorption. The size of as-synthesized nickel NPs was found to be easily controlled by changing synthetic conditions, including P:Ni precursor ratio, reaction temperature, reaction time and oleylamine quantity, and the possible growth mechanism of nickel NPs was proposed. In addition, the magnetic measurements showed that the as-synthesized nickel NPs exhibited superparamagnetism characteristics at room temperature, and the saturation magnetization increased significantly with the increase in nickel NPs’ size. Finally, the size-dependent catalytic properties of nickel NPs for cyclohexane dehydrogenation reaction were studied. The results demonstrated that the catalytic activity can be enhanced by decreasing the size of NPs, which indicated that the dehydrogenation reaction of cyclohexane on nickel NPs was structure sensitive reaction.

Performance enhancement of thermally coupling of methanol synthesis, DME synthesis and cyclohexane dehydrogenation processes: Employment of water and hydrogen perm-selective membranes via different recycle streams

In this research, effect of water and hydrogen perm-selective membranes via different recycle cases in a thermally double-coupled two-membrane reactor (TDCTMR) has been investigated. Methanol and direct dimethyl ether (DME) synthesis from natural gas as exothermic reactions have been thermally coupled with cyclohexane dehydrogenation as an endothermic reaction. Hydroxy sodalite (H-SOD) and Pd/Ag membranes have been employed for removing water from methanol side and injection of hydrogen to DME side respectively. Three different recycle stream cases have been studied for the performance enhancement of TDCTMR. In the first case, the outlet stream from DME reactor is recycled to itself. Also, in the second case, the outlet stream from methanol side is recycled to DME side and finally, the third case is that the mixture of methanol and DME outlet streams are recycled to DME side. The results of these three cases are compared with thermally double coupled reactor (TDCR). Results show that hydrogen production in cyclohexane side of TDCTMR increases 8.32%, 22.89% and 23.88% for cases 1, 2 and 3 in comparison to TDCR respectively. Also, DME and methanol production enhances 38.38% and 13.3% for case 3 (best case) in comparison to TDCR respectively.

Vanadium-Node-Functionalized UiO-66: A Thermally Stable MOF-Supported Catalyst for the Gas-Phase Oxidative Dehydrogenation of Cyclohexene

The OH groups on the Zr-based nodes of ultrastable UiO-66 can be metallated with VV ions in a facile fashion to give the derivative VUiO-66. This metallated MOF exhibits high stability over a broad temperature range and displays high selectivity for benzene under low-conversion conditions in the vapor-phase oxidative dehydrogenation of cyclohexene (activation energy ∼110 kJ/mol). The integrity of the MOF is maintained after catalysis as determined by PXRD, ICP-AES, and SEM.

Formation of ilmenite-type CoTiO3 on TiO2 and its performance in oxidative dehydrogenation of cyclohexane with molecular oxygen

Ilmenite-type CoTiO3 supported on TiO2 was prepared and their catalytic activities were tested for oxidative dehydrogenation of cyclohexane to produce benzene. The catalyst was characterized by XRD, FE-SEM, HR-TEM, XPS, TPR and XANES. XRD reveals the formation of ilmenite-type CoTiO3 on TiO2. The catalyst showed 87.8% cyclohexane conversion with 89.2% benzene selectivity at 450°C in a continuous fixed bed down flow reactor at atmospheric pressure. The influence of different reaction parameters like temperature, gas hour space velocity (GHSV), Co loading was studied in detail.

The Progress of Catalyst for Cyclohexane Dehydrogenation Processes

Cyclohexane dehydrogenation is an important process in the petrochemical industry, chemical raw material such as cyclohexanol, cyclohexanone,benzene and cyclohexene can be produced from which.Divided cyclohexane dehydrogenation into catalytic dehydrogenation or oxidative dehydrogenation, homogeneous or heterogeneous reaction. Summarized vary catalysts, active constituent and process conditions in dehydrogenation process.

Influence of Time and Temperature on the Regeneration of PtReIn/Al2O3 Naphtha Reforming Catalysts

The influence of temperature (450–500 °C) and time (1–4 h) of coke combustion on the catalytic properties of PtReIn/Al2O3 were studied. The results of the cyclohexane dehydrogenation and cyclopentane hydrogenolysis reactions show that the regeneration treatment with diluted oxygen can fully recover the activity of the metal function despite some observed segregation of Re and In. In the case of the n-heptane reforming reaction, the regenerated catalysts had lower activity and stability than the fresh ones. The experiments at high temperature in air showed that In prevents the sintering of Pt and Re but at 650 °C a segregation of Re from the Pt–Re phase occurs.

The optimal operating conditions of a thermally double coupled, dual membrane reactor for simultaneous methanol synthesis, methanol dehydration and methyl cyclohexane dehydrogenation

In this study, the concept of thermally double coupled reactor is proposed as an alternative configuration to mix the energy efficient concept of coupling two exothermic with one endothermic reaction. In this multi-tubular fixed bed reactor, methanol synthesis and methanol dehydration, as two exothermic reactions occur in the inner and outer tubes while the methyl cyclohexane dehydrogenation, as an endothermic reaction takes place in the middle tube. Two water permselective membranes are also applied in the inner and outer tubes to remove water from both exothermic sides. Extraction of water as one of the main byproducts in the DME (dimethyl ether) and methanol synthesis processes increases the production rate and the catalyst life time. In this configuration, the operating conditions are optimized using a differential evolution method in order to maximize the outlet methanol and DME mole fractions of the inner and outer exothermic sides respectively. Then the optimized results of the thermally double couple dual membrane reactor are compared with the optimized thermally double couple reactor and the ones in conventional methanol and DME synthesis reactors. This comparison shows the superiority of this configuration to the conventional ones owing to the enhancement of methanol and DME mole fractions (10.9% and 19.5% increase compared with conventional ones respectively). Hydrogen and toluene, as two valuable products, are also produced in a favorable mode.

Influence of Na content on the catalytic properties of Pt-Ir/Al2O3 catalysts for selective ring opening of decalin

The influence of the Na addition on Pt-Ir/Al2O3 on the reaction of selective ring opening of decalin and methyl cyclopentane was studied. The catalysts were evaluated by means of TPR, pyridine TPD, TEM, FTIR-CO and by the reaction tests of cyclohexane dehydrogenation, hydrogenolysis of cyclopentane, selective ring opening of decalin and methyl cyclopentane. It was found that Na strongly decreases the acidity and influences the metal properties of Pt-Ir/Al2O3 catalysts. The interaction between Pt and Ir is increased by the presence of Na, with larger metal crystals being obtained on the support modified by Na. As a consequence, the catalytic properties are also modified and the CP/CH ratio (parameter of demanding/not demanding reaction) is increased with sodium concentration. In the case of MCP reaction, Na strongly decreases the aromatic and n-C6 formation and favors the selective reaction mechanism, thus favoring the formation of 2MP and 3MP. For the decalin reaction, it was found that the yield to the dehydrogenated product of the catalysts supported on Al2O3-Na is lower than that of the free Na-alumina supported catalyst, whereas the opposite occurs with the yield to C1 due to the higher hydrogenolytic and lower dehydrogenation activity of the catalysts with Na. The yield to ring contraction (RC) products is higher on the catalyst without Na due to the higher acidity which favors the ring contraction reaction and the lower metallic activity; thus, the transformation of the RC product to ring opening products is decreased.

An insight into spray pulsed reactor through mathematical modeling of catalytic dehydrogenation of cyclohexane

A mathematical model has been developed to study the impact of nozzle-catalyst distance and bulk gas temperature on the conversion and hydrogen evolution rate in a spray pulse reactor. The effects of reactor configuration and operating parameters on conversion and evolution rate were predicted with more than 90% accuracy. Reactor optimization and sensitivity analysis were carried out and an optimal design of nozzle-catalyst distance 5 cm and bulk gas temperature of 50 °C were proposed. The optimized design was predicted to increase the conversion from approximately 32–74%. The model could be in general used for designing any endothermic heterogeneous catalytic reaction in a spray pulse reactor.

Various characteristics of Ni and Pt–Al2O3 nanocatalysts prepared by microwave method to be applied in some petrochemical processes

Alumina-supported metal nanocatalysts were prepared via the microwave method, by loading nano Ni particles (at 1, 3 and 5wt%) or nano Pt particles (at 0.3, 0.6 and 0.9wt%). Structural and adsorption features of the nano catalysts were revealed through XRD, DSC-DTA, TEM, H2-chemisorption and N2-physisorption. N2-adsorption–desorption isotherms of type IV were related typically to mesoporous materials with H2 class of hysteresis loops characterizing ink bottle type of pores. The well dispersed nano-sized metal particles were evidenced in the studied catalytic systems, exhibiting marked thermal stability up to 800°C. The catalytic performances of different catalyst samples were assessed during cyclohexane, normal hexane and ethanol conversions, using the micro-catalytic pulse technique at different operating conditions. The 5% Ni–γ–Al2O3 sample was found to be the most active in dehydration of ethanol to produce ethylene, as well as in n-hexane cracking. However, the 1% Ni–Al2O3 sample showed the highest dehydrogenation activity for selective production of benzene from cyclohexane. On the other hand, the 0.9% Pt–γ–Al2O3 sample exhibited the highest activity in the dehydration of ethanol and in the dehydrogenation of cyclohexane. The 0.3% Pt–γ–Al2O3 sample was the most active in the dehydrocyclization of normal hexane, as compared to the other catalyst samples under study.

Catalytic properties of Pt-based intermetallic compounds in dehydrogenation of cyclohexane and n-butane

A series of Pt-based intermetallic compounds supported on silica (PtmMn/SiO2: M=Co, Ge, Sn, Tl and Zn) were prepared by conventional impregnation and chemical vapor deposition. Catalytic properties of the intermetallic compounds in dehydrogenation of cyclohexane and n-butane were investigated. Pt3Sn/SiO2 and PtGe/SiO2 showed higher yields of benzene and butenes than Pt/SiO2 and other intermetallic catalysts (Pt3Zn, Pt3Co, PtCo, Pt3Tl2 and PtSn). Especially in n-butane dehydrogenation, Pt3Sn/SiO2 exhibited much higher butenes yield than other intermetallic catalysts and Pt/SiO2. However, a similar Pt–Sn intermetallic catalyst, PtSn/SiO2, showed very poor yields in both reactions. Pt3Sn and PtSn, Pt3Sn was the most active species in the n-butane dehydrogenation among several Pt–Sn bimetal phases, Pt1−xSnx solid solution (0<x<0.3).

Non-noble Ni–Cu/ACC bimetallic catalyst for dehydrogenation of liquid organic hydrides for hydrogen storage

The effect of Cu on dehydrogenation activity of Ni has been observed when dehydrogenation of methyl cyclohexane (MCH) was carried out by using bimetallic Ni–Cu supported on activated carbon cloth (ACC) catalysts with various Ni to Cu ratios and constant total metal content of about 10 wt%. The dehydrogenation of MCH was studied for delivery of clean hydrogen to hydrogen fueling station. Catalysts have been synthesized by adsorption method and characterized by atomic absorption spectroscopy (AAS), X-ray powder diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Among all combinations of this study 8 wt% Ni + 2 wt% Cu/ACC was found to show strong synergetic effect. This catalyst exhibited relatively high H2 evolution rate 39.4 mmol/gmet/min during the dehydrogenation of MCH. At the same time methane evolution rate was relatively low which indicated insignificant side reaction of hydrogenolysis. The study reveals that presence of specific amount of Cu enhances the dehydrogenation activity of Ni and suppresses the hydrogenolysis activity for the same. The Ni–Cu/ACC catalyst may be a potential non-noble metal catalyst for dehydrogenation reaction.

The catalytic performance of Ni2P/Al2O3 catalyst in comparison with Ni/Al2O3 catalyst in dehydrogenation of cyclohexane

The Ni2P/γ-Al2O3 and Ni/Al2O3 catalysts were prepared, characterized, and evaluated for dehydrogenation of cyclohexane. The Ni2P/Al2O3 catalyst exhibited superior activity, selectivity and stability to those of the Ni/Al2O3 catalyst. Characterization results indicate that the small positive charge of Ni and the ensemble effect of P in Ni2P can inhibit sintering of Ni2P and promote reactivity of Ni2P in dehydrogenation of cyclohexane. Moreover, the in situ Fourier transform infrared spectra further reveal that the P-covered Ni(2) sites (Ni3P_P sites) of Ni2P(0001) are responsible for dehydrogenation of cyclohexane. Meanwhile, the hydrogen temperature-programmed desorption experiments indicate that the Ni2P/Al2O3 catalyst contains a large amount of the Ni(2) sites.

N-decane dehydrogenation on bimetallic PtSn and PtGe catalysts prepared by dip-coating

The catalytic performance of Pt, PtSn and PtGe supported on γ-Al2O3 (γ-A) deposited by dipcoating of spheres of α-Al2O3 (α-A) was studied in the n-decane dehydrogenation. The effect of Sn and Ge addition to Pt on the activity and selectivity was analyzed. The catalytic characterization was carried out using cyclohexane dehydrogenation (CHD), cyclopentane hydrogenolysis (CPH), temperature-programmed reduction (TPR), hydrogen chemisorption, X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA) and scanning electronic microscopy (SEM). Pt(0.5)Sn/γ-A/α-A catalyst had the best catalytic performance and showed a low electronic interaction between the metals, with a surface segregation of Sn and the presence of oxidized Sn stabilized on the support. PtGe catalysts presented strong interactions with probable alloy formation. The catalytic performance of these catalysts is comparable to that reported in the patents.

Study of Monometallic Pd/TiO2 Catalysts for the Hydrogenation of Succinic Acid in Aqueous Phase

A series of 2 wt % Pd/TiO2 monometallic catalysts were prepared by varying some parameters, such as the nature of the precursor salt, the titania support, and the preparation method. The structural and textural properties of the catalytic systems were fully characterized by several physical and chemical techniques (inductively coupled plasma optical emission spectrometry, N2 physisorption, H2 chemisorption, transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy, powder X-ray diffraction, temperature-programmed reduction, X-ray photoelectron spectroscopy, and gas phase reaction of cyclohexane dehydrogenation). The catalytic performances were further estimated for the hydrogenation of an aqueous solution of succinic acid (SUC) performed in a batch reactor at 160 °C and under 150 bar total pressure. The results showed that all the Pd catalysts are very selective to produce γ-butyrolactone, the first hydrogenated product. However, the rate of succinic acid conversion is a function ...

Effect of Steam on the Reaction Performance of Oxidative Dehydrogenation of Cyclohexane

The effect of steam, fed to the fixed-bed microreactor reactor, on the oxidative dehydrogenation of cyclohexane over Mg3(VO4)2 catalyst was reported. The catalyst characterization results showed that the crystal structure, the electron cloud distributions of the active species and the oxygen species, and the reducibility of the active species are not influence by the introduction of steam. It was observed that steam added to the oxidative dehydrogenation of cyclohexane competes for sites required for gas-phase oxygen activation, which catalyst lattice oxygen utilization is not affected. The shorter residence time and the competition for sites with oxygen causes a decrease in cyclohexane conversion and a corresponding increase in selectivity to cyclohexene.