Transformation Of Cyclohexane Research Articles

Desulfurization reactions of thiophene and cyclohexane over Zn and Nb modified zeolites in FCC process

In refineries, one of the most important production units is Fluid Catalytic Cracking (FCC). In them, the incorporation of additives to the catalyst is a very interesting option to reduce the sulfur content of gasoline, and thus obtain commercial fuel specifications. In this study, the transformation of thiophene into a cyclohexane (HC) stream for its in-situ desulfurization has been investigated, using catalysts based on niobium or zinc (6 wt%) incorporated into three types of zeolites: HUSY, HBeta and HZSM-5. Catalytic tests were carried out at 773 K in an automatically controlled fixed-bed tubular reactor. The reaction products were analyzed online by gas chromatography, with FID detector for hydrocarbons and SCD for sulfur compounds, and the catalysts were characterized by XRD, FTIR, N2 adsorption isotherms, HRTEM, XRF, 29Si and 27Al solid state NMR, NH3-TPD and FTIR-pyridine techniques. The results indicate that the addition of metals did not significantly alter the textural and structural properties of the zeolites, and that the Nb/HB and Nb/HY catalysts were the most effective in the conversion of thiophene, and selective toward paraffins and H2S mainly. The performance of these materials was attributed to the existence of an optimal balance between the Brønsted and Lewis acid sites, which increased the hydrogen transfer coefficient (HTC) during the cyclohexane transformation, resulting in higher desulfurization activity. The addition of zinc drastically increased the density of the Lewis acid sites and decreased the HTC, favoring the production of aromatics and thiophene condensation reactions, thus transferring sulfur to the gasoline streams. In general, the catalysts investigated are of significant interest as additives for sulfur reduction in FCC gasoline streams, either by producing easily removable H2S or by transferring sulfur to heavier fractions.

Highly selective aerobic oxidation of cyclohexane by flower-like MoO3-x microspheres-nitrogen-doped carbon dots heterojunction

Due to the higher susceptibility of alcohols and ketones to oxidation compared to alkanes, converting inert C-H bonds in alkanes into high value-added product KA oil with high selectivity is still a significant obstacle. In this study, flower-like microspheres of MoO3-x, featuring aligned nanosheets and oxygen vacancies, were combined with nitrogen doped carbon dots (NCDs) to fabricate S-scheme heterojunctions of MoO3-x-NCDs for boosting the photocatalytic efficiency in oxidizing cyclohexane. Because of the oxygen vacancies-triggered localized surface plasmon resonance (LSPR) and the S-scheme charge transfer mechanism, there was a significant improvement in the absorption of visible light and an enhancement in the efficiency of charge separation. The MoO3-x-NCDs composites exhibited a notably improved catalytic performance in cyclohexane oxidation. The MoO3-x-NCDs composite exhibited remarkable selectivity of KA oil in catalyzing cyclohexane oxidation under light exposure, attributed to the substantial increase in cyclohexane adsorption capacity. The highest cyclohexane transformation rate of 9.98 % was achieved by MoO3-x-NCDs-2 composites with a MoO3-x/NCDs ratio of 50:1, outperforming bare MoO3-x by 1.81 times, while exhibiting a KA oil selectivity reaching 93.75 %. The mechanism of selective photocatalytic oxidation was explored using photoelectric examination, analysis of energy bands, and evaluation of active radicals. In this research, green photocatalysts were fabricated through the utilization of NCDs, enabling efficient conversion and selective oxidation of cyclohexane in gentle environments. This innovative approach holds great potential for advancing the field of photocatalysis.

Interfacial hydrogen bond effect between CeO2 and g-C3N4 boosts conversion to adipic acid from aerobic oxidation of cyclohexane

The selective oxidation reaction of cyclohexane is one of the typical activated sp3 C-H reactions, and its product adipic acid (AA) is the indispensable raw material used to produce nylon. However, subjecting to the inertness of C-H bond and the great reactivity of AA, the targeted transformation of cyclohexane remains a challenge. Here, the interfacial hydrogen bond (IHD) was developed by anchoring CeO2 on graphite carbon nitride (g-C3N4) surface, which could boost targeted acquisition adipic acid from aerobic oxidation of cyclohexane. The results indicated that the IHD effect can be flexibly regulated by changing the ratio of Ce3+/Ce4+, further optimizing the properties of surface OH species and Lewis acid sites. Under the synergistic effect of Ce3+/Ce4+ and Lewis acid sites on reaction interface, the glorious performance (32.2% conversion of cyclohexane with 66.4% selectivity) was obtained over the as-prepared CeO2/g-C3N4 IHD system. In addition, the interfacial adsorption properties of cyclohexane were explored by the virtue of in situ infrared spectroscopy, revealing the IHD effect could tune the adsorption behavior of cyclohexanone and further improve the selectivity of AA. This work disclosed that engineering the interface hydrogen bond effect between CeO2 and g-C3N4 provided feasible strategies to obtain excellent catalyst for cyclohexane oxidation.

Honeycomb-like porous Ce–Cr oxide/N-doped carbon nanostructure: Achieving high catalytic performance for the selective oxidation of cyclohexane to KA oil

In heterogeneous catalysis, developing robust catalysts and preventing the metal leaching during the reactions still remain challenging. Herein, a porous honeycomb-like nanostructure with bimetallic Ce–Cr oxide supported on N-doped carbon was prepared via a facile in-situ pyrolysis method. The prepared catalyst was highly active, selective, and stable in the transformation of cyclohexane to KA oil with H2O2 as the oxidant. The N-doped carbon served as an excellent support for the metal nanoparticles and greatly promoted their dispersion, and displayed a comparable or superior catalytic activity compared to the other traditional supports. It was found that the pyridinic N and pyrrolic N species of N-doped carbon were the main active sites for the metal immobilization, and the strong electronic interaction between N-doped carbon and Ce–Cr oxide was formed. The results revealed that the increased low-valence metal species might be responsible for the improved catalytic activity, and EPR analysis indicated that the hydroxyl radicals played a crucial role during the oxidation process. Besides, the catalyst can be easily separated and still remained stable after recycling seven times, making it a promising candidate for the catalytic oxidation of cyclohexane to KA oil under mild conditions.

Propane aromatization on hierarchical Ga/HZSM-5 catalysts

Gallium containing ZSM-5 zeolites were prepared by ion exchange and mechanical mixture from the parent ZSM-5 and two desilicated zeolites to be tested in propane aromatization. The alkaline treatment was made by sodium hydroxide, with or without tetrabutylammonium hydroxide. The catalysts prepared from desilicated zeolites are less active in propane aromatization and cyclohexane transformation and less selective into aromatics than those prepared from the parent zeolite. The desilication did not affect the acid properties, especially the strength of acid sites as seen by CO adsorption at 77 K and n-hexane cracking.

Photoinduced Direct Conversion of Cyclohexane into Cyclohexanone Oxime using LEDs

AbstractA selective direct photochemical transformation of cyclohexane into cyclohexanone oxime using tert‐butyl nitrite and UV LED diodes is described. The reaction allows the direct introduction of an oxime group into a hydrocarbon using a simple set‐up in one step that proceeds in a clean fashion, a transformation which technically would require several steps. This straightforward method may provide a valuable alternative to significantly more expensive common procedures for the synthesis of cyclohexanone oxime, a key precursor to the Nylon‐6 polymer.

Synthesis, characterization and catalytic performance in cyclohexane transformation by Bi2O3/MCM-41 nanocomposite materials

ABSTRACT The nanoparticles of Bi2O3 supported on mesoporous MCM-41 were prepared in a simple way and were well characterized. The oxidation of cyclohexane to cyclohexanol and cyclohexanone under 1 atmospheric pressure of air in the absence of any solvent and reducing agents with Bi2O3/MCM-41 nanocomposites were considered. These nanoparticles of Bi2O3 supported on mesoporous MCM-41 were found to be the very effective catalysts for cyclohexane oxidation with air in a temperature range of 280–370 ˚C. The influences of reaction temperature, the loading amount of Bi2O3 and space velocity on the oxidation of cyclohexane were also studied, and optimized conditions were investigated.

Cyclohexane in nanotubes: Direct chair–chair interconversion

DFT PBE/3ζ study of conformational transformations of cyclohexane inside nanotubes with chirality indices of (8,0) and (5,5) showed that the encapsulated molecule is characterized by shortened C–C bonds, some electric charge, and reduced barrier to chair–chair interconversion in comparison to the free molecule. Unlike free cyclohexane, no twist conformer as intermediate minimum on the potential energy surface was localized for the encapsulated molecule.

Bifunctional H2WO4/TS-1 catalysts for direct conversion of cyclohexane to adipic acid: Active sites and reaction steps

Adipic acid production may account for 10% of the annual increase in atmospheric nitrous oxide level. Here we developed a hollow H2WO4/TS-1 bifunctional catalyst with excellent catalytic activity for the direct transformation of cyclohexane to adipic acid with 30% hydrogen peroxide by a non-HNO3 route. XRD diffraction, N2 physisorption, TEM, NH3-TPD and Raman, XPS, Infrared, and UV–visible spectroscopies were used to characterize catalysts to increase understanding of the structure of active species on the hollow TS-1 support. The enhanced catalytic activity in comparison of reference catalysts (H2WO4, H2WO4/Silicate-1 and TS-1) was explained in terms of their bifunctional catalytic sites and perfect hollow morphology with large intraparticle voids. Experimental results on the product distribution indicated that the tetrahedral Ti and surface W sites played important roles in the synergistic effect: tetrahedral Ti worked in oxidation of cyclohexane to intermediates (cyclohexanone and cyclohexanol) and surface W worked in further oxidation of late intermediates to adipic acid. Theoretical calculation results on catalytic activity of the TiOOH and WOOH active sites in the H2WO4/TS-1 for different reaction steps validate the experimental results. The catalytic activity was also correlated to the strong interaction between W sites and HTS-1 surface induced increase in acidity of the materials. Increasing calcination temperature led to structural evolution of supported active species and subsequent activity change. A cyclohexane conversion of 31% with 78% adipic acid selectivity was achieved over this catalyst calcinated at 500 ∘C. Based on the catalytic and characterization results, possible reaction pathways were thus proposed to explain high adipic acid yield over hollow H2WO4/TS-1 catalysts.

Exploring the reaction pathways of Pd(ii)-catalyzed cyclohexene oxidation with molecular oxygen: vinylic and allylic oxidation, disproportionation and oxidative dehydrogenation

Palladium(ii) salts are able catalysts to promote different oxidative transformations of cyclohexene in the presence of molecular oxygen: vinylic and allylic oxidation and disproportionation.

Novel cyclohexane monooxygenase from Acidovorax sp. CHX100

Acidovorax sp. CHX100 has a remarkable ability for growth on short cycloalkanes (C5-C8) as a sole source of carbon and energy under aerobic conditions via an uncharacterized mechanism. Transposon mutagenesis of Acidovorax sp. CHX100 revealed a novel cytochrome P450 monooxygenase (CYP450chx) which catalyzed the transformation of cyclohexane to cyclohexanol. Primer walking methods categorized CYP450chx as cytochrome P450 class I taking into account its operon structure: monooxygenase, FAD oxidoreductase, and ferredoxin. CYP450chx was successfully cloned and expressed in Escherichia coli JM109. The activity of CYP450chx was demonstrated by means of the indole co-oxidation. Biotransformation capability of CYP450chx was confirmed through the catalysis of cycloalkanes (C5-C8) to their respective cyclic alcohols.

Fe-amino acid complexes immobilized on silica gel as active and highly selective catalysts in cyclohexene epoxidation

In this work, the syntheses, structure, superoxide dismutase (SOD) activity, and the catalytic use in the oxidative transformations of cyclohexene of covalently grafted Fe(III)-complexes formed with various or various combinations of C-protected amino acid (l-histidine, l-tyrosine, l-cysteine and l-cystine) ligands are presented. The structural features of the surface complexes were studied by XANES/EXAFS and mid/far-IR spectroscopies. The compositions of the complexes were determined by ICP-MS and the Kjeldahl method. The SOD activities of the materials were evaluated in a biochemical test reaction. The obtained materials were used as catalysts for the oxidation of cyclohexene with peracetic acid in acetone. Both covalent grafting and building the complex onto the surface of the chloropropylated silica gel were successful in most cases. In many instances, the obtained structures and the coordinating groups were found to substantially vary upon changing the conditions of the syntheses. All the covalently immobilized Fe(III)-complexes displayed SOD activities, and most of them were found to be capable of catalyzing the oxidation of cyclohexene with appreciably high activities and outstanding epoxide selectivities.

Microporous–mesoporous ZSM-12 zeolites: Synthesis by using a soft template and textural, acid and catalytic properties

The influence of the amount of amphiphilic organosilane TPOAC {[3-(trimethoxy-silyl)propyl] octadecyldimethylammonium chloride} added in the synthesis and of the crystallization time in the textural, acid and catalytic properties of microporous–mesoporous ZSM-12 (MMZ12) zeolites was investigated. XRD/Rietveld Refinement, N2 sorption measurements, SEM, EDX, and NH3-TPD were used to sample characterization and the performance as acid catalysts verified using the transformation of cyclohexane as a model reaction. WAXRD data showed that the usage of short synthesis times and increasing amounts of TPOAC in the synthesis led to ZSM-12 zeolites with poor crystallinity due to the organosilane steric constraints to MTW nuclei formation and crystal growth. On the other hand, SAXRD and N2 sorption data evidenced that TPOAC firstly generates a pseudo-ordered mesoporous phase, which is transformed into well-crystalline hierarchical MMZ12 zeolites tailoring the synthesis conditions. Were obtained samples with a relatively broad mesopore size distribution having mean diameters close to 4.0nm and slightly higher external surface areas and lower amounts of strong acid sites than the only microporous ZSM-12 one. The MMZ12 zeolites showed similar cyclohexane conversion and lower deactivation rate due to coke formation than a conventional ZSM-12 that were attributed to a balance of two opposite effects, a lower strong acidity and the presence of HRTEM evidenced interconnected micropores and mesopores that reduce the 3D internal diffusion limitations. The yield and selectivity on the conventional ZSM-12 were coherent with the transformation of cyclohexane on 12-ring H-zeolites, nevertheless on the microporous–mesoporous ones the yield to C6 saturated hydrocarbons increased with the increase of the mesoporous volume, then disfavoring the yield to saturated and unsaturated light hydrocarbons.

ChemInform Abstract: Stereocontrolled Transformation of Cyclohexene β‐Amino Esters into syn‐ or anti‐Difunctionalized Acyclic β2,3‐Amino Acid Derivatives.

ChemInform Abstract: Stereocontrolled Transformation of Cyclohexene β‐Amino Esters into syn‐ or anti‐Difunctionalized Acyclic β^2,3‐Amino Acid Derivatives.

Isolation and characterization of two novel strains capable of using cyclohexane as carbon source.

Two strains capable of degrading cyclohexane were isolated from the soil and sludge of the wastewater treatment plant of the University of Stuttgart and a biotrickling filter system. The strains were classified as gram negative and identified as Acidovorax sp. CHX100 and Chelatococcus sp. CHX1100. Both strains have demonstrated the capability to degrade cycloalkanes (C5-C8), while only strain CHX1100 used as well short linear n-alkanes (C5-C8) as the sole source of carbon and energy. The growth of Acidovorax sp. CHX100 using cyclohexane was much faster compared to Chelatococcus sp. CHX1100. Degenerated primers were optimized from a set sequences of cyclohexanol dehydrogenase genes (chnA) as well as cyclohexanone monooxygenases (chnB) and used to amplify the gene cluster, which encodes the conversion of cyclohexanol to caprolactone. Phylogenetic analysis has indicated that the two gene clusters belong to different groups. The cyclohexane monooxygenase-induced activity which oxidizes also indole to 5-hydroxyindole has indicated the presence of a CYP-type system monooxygenase involved in the transformation of cyclohexane to cyclohexanol.

Synthesis, structural characterisation, and catalytic activity of Mn(II)–protected amino acid complexes covalently immobilised on chloropropylated silica gel

In this work the syntheses, structure, superoxide dismutase (SOD) activity and the catalytic use in the oxidative transformations of cyclohexene of covalently grafted Mn(II)–complexes formed with various C-protected amino acid (l-histidine, l-cysteine and l-cystine) ligands are presented. The structural features of the surface complexes were studied by EPR, X-ray absorption, and mid/far IR spectroscopies. The superoxide dismutase activities of the materials were determined in a biochemical test reaction. The obtained materials were used as catalysts for the oxidation of cyclohexene with peracetic acid in acetone. Covalent grafting and building the complex onto the surface of the chloropropylated silica gel were successful in all cases. It was found that in many instances the structures obtained and the coordinating groups substantially varied upon changing the conditions of the syntheses. All the covalently immobilised Mn(II)–complexes displayed superoxide dismutase activity and could catalyse the oxidation of cyclohexene.

Oxydation Entraînée des Hydrocarbures. II. Influence des sels de Cobalt

In the autoinitiated oxidation of pure cyclohexane in the liquid phase at 150°C and under an initial partial pressure of oxygen ot 11kg/cm2, the salt of cobalt reduces the time of induction, but does not increase the rate of transformation. On the other hand, in the oxidation of the mixture cyclohexanecumene, the rate of transformation of cyclohexane is increased, and this increase is more pronounced by the addition of cobalt naphtenate. The induction period decreases with higher cumene or cobalt concentration. The differences between the observed and calculated effects, on the base of deduced kinetical relations, are interpreted as an increase in the chain branching degree when cumene is present. The stability of the cumylperoxydic radicals is related to the effect.

The effect of alumina on FCC catalyst in the presence of nickel and vanadium

Although several works studied the effect of metals on Y zeolites in the FCC process, only a few focused on the role of other FCC catalyst components such as silica (binder) and alumina (matrix). Aiming to understand the matrix effect on metal distributions on the catalyst components – which can impact its deleterious properties – two FCC model catalysts were modified with nickel and/or vanadium. One consisted of USY zeolite, silica and kaolin, the other contained the same components plus alumina. The catalysts were characterized by three model reactions: ethane hydrogenolysis, cyclohexane transformation and n-hexane cracking. Also, textural properties, temperature-programmed reduction (TPR) and elemental mapping analyses were performed to characterize both nickel and vanadium distributions (throughout) the alumina ingredient. In the absence of metals, both catalysts showed similar catalytic activity and selectivity in n-hexane cracking reaction, indicating that the zeolite sites are responsible for the activity. The n-hexane activity largely decreased in the presence of nickel regardless of the presence of alumina. On the other hand, the presence of alumina allows the catalyst to retain more n-hexane activity and microporosity after vanadium introduction. Vanadium was homogeneously distributed in the catalyst without alumina, while in the presence of alumina the mapping results indicate some areas of higher vanadium concentration. After oxidation thermal treatment for V–alumina catalyst, all catalysts showed loss in the n-hexane activity. However, the relative rates between the catalyst with and without vanadium were retained suggesting that the distribution of V did not change. Cyclohexane and ethane hydrogenolysis model reaction data implied that the coke formation on nickel particles was limited due to metal–alumina interaction.

ChemInform Abstract: Transformation of Cyclohexene to Enantiopure Cyclitols Mediated by Sequential Oxyselenenylation with (S,S)-Hydrobenzoin: Synthesis of D-chiro-Inositol and muco-Quercitol.

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Structural properties of an unsupported model Pt–Sn catalyst and its catalytic properties in cyclohexene transformation

Unsupported PtSn powder was prepared by direct reduction of a solution containing both H 2PtCl 6 and SnCl 4 using hydrazine as the reducing agent. The dark gray powder was characterized with scanning electron microscopy (SEM), EDX analysis, Mössbauer spectroscopy, X-ray diffraction, XPS depth profiling after different treatments: presintering, O 2 and H 2 treatments. SEM showed a conglomerate of small spherical particles (0.2–1.5 μm). They contained Pt, various PtSn alloy phases and tin-oxide(s). EDX showed 70–75% Pt and 25–30% Sn on various grains. The mixture of Pt 3Sn and SnO 2 represented the final stabilized state obtained upon repeated heating in air and, finally, H 2. This mixed Pt–Sn was catalytically inactive in “structure-sensitive” reactions, such as methylcyclopentane ring opening or cyclohexane dehydrogenation, but was active in “structure-insensitive” hydrogenation and also in the dehydrogenation of cyclohexene. The relative importance of the latter two reactions depended strongly on the previous treatments of the catalyst—i.e., on its composition, the final stage (Pt 3Sn and SnO 2) being most active, with cyclohexane as the main product.