High Isomerization Research Articles

Role of support in deoxygenation and isomerization of methyl stearate over nickel–molybdenum catalysts

Microporous SAPO-11 and highly ordered mesoporous AlSBA-15 with different aluminum contents (with Si/Al ratio of 5 and 10) were synthesized. Thus prepared samples were characterized by BET, pyridine-FTIR and NH3-TPD to investigate their structural and acidic properties. The samples were then transformed into bifunctional catalysts by loading with molybdenum and nickel. Their activities were tested in the hydroconversion of methyl stearate using a fixed bed flow reactor system. The sulfided NiMo catalysts exhibited high conversion and deoxygenation activities. High isomerization activities observed for both NiMo/SAPO-11 and NiMo/AlSBA-15 catalysts, similar to the isomerization of light naphtha, was attributed to the acidity of supports. However, the acidity of supports was not the only factor influencing the isomerization of long chain molecules. AlSBA-15 had a large specific surface area that contained more acidic sites inside of its channels, promoting the formation of cracking products; SAPO-11 had a suitable pore size and contained fewer acidic sites inside the pore channels, promoting the formation of mono-branched isomers while suppressing cracking reactions.

Optimization for Ultra High Pressure Isomerization of Lycopene

To isomerizate of lycopene by ultra high pressure (UHP) method, based on single factor experiments, orthogonal test was used to optimum the isomerization conditions. UHP pressure, UHP holding time, temperature were as factors and ratio of cis-lycopene in total lycopene was as index. The results were as follows: 50°C, UHP pressure 500MPa and holding time 7min. The ratio of cis-lycopene in total lycopene was 45.1%. So UHP combine heating has a isomerization effect on lycopene.

One-step hydrodeoxygenation of palm oil to isomerized hydrocarbon fuels over Ni supported on nano-sized SAPO-11 catalysts

Nano-sized SAPO-11s were hydrothermally synthesized with using di-n-propylamine (DPA) as structure-directing agent in mixed n-tetradecanoamine–n-propanol–H2O medium and the Ni/SAPO-11 catalysts were prepared by incipient wetness impregnation. The catalysts was characterized by XRD, SEM, BET, H2-TPR, NH3-TPD and TG techniques and their catalytic performance was tested in hydrodeoxygenation (HDO) of palm oil to hydrocarbon fuels. Surfactant n-tetradecanoamine could mediate the minimum SAPO-11 sizes into 20–50nm. As comparing to the commercial SAPO-11, the nano-sized SAPO-11s presented significantly enlarged surfaces and mesoporous volumes, which offered sufficient space and strong interactions for dispersing Ni. One-step HDO of palm oil demonstrated that the nano-sized SAPO-1 supported Ni catalysts showed the high yield (80%) of liquid hydrocarbons, high isomerization selectivity (80%) and excellent stability due to that the catalyst presented appropriate acidity, higher Ni dispersity, balance of metal (Ni) and acid (SAPO-11) functionalities and fast diffusion for bulky palm oil and products. These promotion effects observed over the nano-sized SAPO-11 supported Ni catalysts indicated the potential application in biorefinery of vegetable oils to hydrocarbon fuels.

How does the isomerization rate affect the photoisomerization-induced transport properties of a doped molecular glass-former?

We investigate the effect of the isomerization rate f on the microscopic mechanisms at the origin of the massive mass transport found in glass-formers doped with isomerizing azobenzene molecules that result in surface relief gratings formation. To this end we simulate the isomerization of dispersed probe molecules embedded into a molecular host glass-former. The host diffusion coefficient first increases linearly with f and then saturates. The saturated value of the diffusion coefficient and of the viscosity does not depend on f but increases with temperature while the linear response for these transport coefficients depends only slightly on the temperature. We interpret this saturation as arising from the appearance of increasingly soft regions around the probes for high isomerization rates, a result in qualitative agreement with experiments. These two different physical behaviors, linear response and saturation, are reminiscent of the two different unexplained mass transport mechanisms observed for small or large light intensities (for small intensities the molecules move towards the dark regions while for large intensities they move towards the illuminated regions).

Cracking and isomerization functionalities of bi-metallic zeolites for naphtha value upgradation

Effect of acid and metal functionalities of several mono- and bi-metallic wide pore zeolites such as BEA and Y on the cracking and isomerization properties of n-heptane as well as two industrial naphtha feedstocks have been studied. Among these, the bi-metallic Pt–Cr–HBEA catalyst exhibited appropriate catalytic properties responsible for high isomerization and octane boosting. Detailed studies envision that the role of Cr is bi-functional, namely, to change the acidity of the zeolite support towards the moderate strength responsible for controlled cracking and to promote the reducibility and dispersion properties of the Pt for the effective isomerization reaction. This has resulted in enhancement in research octane number (ΔRON) of two industrial naphtha feedstocks with 22 and 43 units increase in RON along with negligible amount of aromatics, especially benzene that makes the product suitable for gasoline applications. The catalyst exhibited constant performance in the studied period of 70h.

Isomerization of α-pinene oxide in the presence of methyltrioxorhenium(VII)

Abstract The catalytic performance of methyltrioxorhenium(VII) (MTO) has been investigated for the first time in the isomerization of α-pinene oxide (PinOx) into campholenic aldehyde (CPA). The high isomerization activity of MTO is coupled with high selectivity to CPA: CPA yield of up to 87% (100% conversion) was obtained by using α,α,α-trifluorotoluene as solvent at 15 °C. Catalyst recycling is possible in a relatively simple fashion by using MTO coupled to an appropriate ionic liquid. The catalytic application of MTO in the isomerization of PinOx versus the integrated epoxidation–isomerization process of the conversion of α-pinene into CPA is discussed.

Effect of temperature and ph on interconversion between fructose and mannose catalyzed by Thermotoga neapolitana mannose-6-phosphate isomerase

The gene encoding a putative mannose-6-phosphate isomerase (TnMPI) from Thermotoga neapolitana DSM4359 was cloned and expressed in Escherichia coli. TnMPI showed the highest isomerization activity between d-fructose and d-mannose at 75°oC in 50 mM Tris-HCl buffer (pH 7.5) containing 1 mM of Cu2+. TnMPI can be activated by some divalent metal ions, such as Cu2+, Mn2+, and Co2+. In the presence of 1 mM Cu2+, TnMPI activity on conversion from d-fructose to d-mannose was significantly enhanced up to 271% of that without Cu2+. In addition, its isomerization equilibrium between d-fructose and Dmannose was strongly affected by reaction temperature and pH. As reaction temperature decreased from 95 to 55°C, the equilibrium ratio of d-fructose to d-mannose was gradually shifted from 73:27 to 55:45. As reaction pH decreased from pH 8.5 to 5.5, the equilibrium ratio of Dfructose to d-mannose was shifted from 68:32 to 49:51.

Role of nanosized oxide in catalysis on the nanoporous surface of zeolite particles

Based on our studies on the hybrid catalysts of nanosized (ns) oxide with zeolite, products obtained from the isomerization and hydrocracking of heavier n-paraffins and the role of ns oxide were investigated using a tricomponent catalyst of [Ni-Mo/γ-Al2O3], ns oxide, and H-beta zeolite catalyst, which showed high activity, high isomerization selectivity, and mild cracking ability. A concerted effect of the three components was observed. From the observed hybridization state of the catalyst, it was suggested that the concerted effect was obtained because the components become attached to each other. The individual and concerted effects of each component and two components, respectively, were investigated based on the ratio of [Ni-Mo/γ-Al2O3]/[H-beta zeolite], the content of ns oxide, the amount of metal, the type of ns oxide species, and the reduction state of metal. It was confirmed that in order to obtain the highest concerted effect, the ratios of [Ni-Mo/γ-Al2O3]/[H-beta zeolite] and/or ns oxide/zeolite are important. Furthermore, among the ns oxide species, nsAl2O3-nsTiO2 displayed the highest activity and cracking ability with an over-cracking suppression. In addition to increasing the concerted effect in the tricomponent catalyst, the performance of this catalyst could also be further increased by controlling the amount and reduction state of metal.

D3h CN3Be3+ and CO3Li3+: viable planar hexacoordinate carbon prototypes

Searches for planar hexacoordinate carbon (phC) species comprised of only seven atoms uncovered good CX(3)M(3) prototypes, D(3h) CN(3)Be(3)(+) and CO(3)Li(3)(+). The latter is the global minimum. It might also be possible to detect the deep-lying kinetically-viable D(3h) CN(3)Be(3)(+) local minimum, based on its robustness toward molecular dynamic simulations and its very high isomerization barrier.

Alkylphosphonic acid- and small amine-templated synthesis of hierarchical silicoaluminophosphate molecular sieves with high isomerization selectivity to di-branched paraffins

This article proposes a one-step strategy to hydrothermally synthesize SAPO-11 with hierarchical micro- and meso-porous structure. The structure and acidity properties and the isomerization performance of the resulting hierarchical SAPO-11 were extensively characterized and assessed, respectively, and compared with those of a microporous SAPO-11. The results showed that the SAPO-11 with mutually interpenetrating micropores and mesopores had been obtained by introducing tetradecylphosphoric acid into the synthesis system of microporous SAPO-11. Compared with microporous SAPO-11, the hierarchical SAPO-11 had much higher external surface and mesoporous volume, and more active sites with suitable Brönsted acid strength. These advantages endowed the hierarchical SAPO-11-based catalyst with superior isomerization activity, enhanced selectivity to di-branched products, and decreased cracking selectivity. The strategy proposed opens a new route to synthesizing a variety of hierarchical mesoporous SAPO molecular sieves for size-selective catalytic conversions of relatively large hydrocarbon molecules.

Effect of the particle size and surface area of tungstated zirconia on the WO x nuclearity and n-heptane isomerization over Pt/WO 3–ZrO 2

Four series of tungstated zirconia of different surface area ranging from 100 to 20 m 2 g −1 and of micro- and nano-meter crystal size were investigated with respect to nuclearity and reducibility of WO x species, concentration of strong and weak acid sites, and n-heptane isomerization over Pt/WO 3–ZrO 2. The nuclearity of WO x species was analyzed by diffuse reflectance UV–Vis spectroscopy and their reducibility by TPR-H 2. TPD of ammonia distinguished acid sites of different strengths. n-Heptane isomerization proceeds over Pt/WO 3–ZrO 2 in hydrogen/nitrogen mixture at 250 °C. At least four types of WO x species differing in nuclearity were identified in tungstated zirconia by a maxima of absorption at 39 000, 35 000, 30 000 and 27 000 cm −1, intensity of which depended on the surface area, crystal size and WO 3 loading. From the changes in the relative intensities of the characteristic individual bands of WO x species with tungsten loading, at different surface area and crystal size, it follows that at the lowest loading mononuclear W–O–Zr species (39 000 cm −1) and two-dimensional poly-tungstate like WO x species (35 000 cm −1) are formed, which are at loading above a nominal monolayer started to transform into a larger defined WO x , likely tri-dimensional clusters (30 000 cm −1). The absorption maximum at 27 000 cm −1 corresponds to bulk-like WO 3. The nuclearity of WO x species was reflected in their reducibility, which increased with increased nuclearity, and it was higher for the nano-size tungstated zirconia. The isomerization activity followed the relative population of poly-tungstate WO x species (35 000 cm −1), but was not in strict agreement with the concentration of strong acid sites. This might be connected with the rate determining step of the isomerization process or formation of radical cations depending on reaction conditions. The nano-size tungstated zirconia exhibited high isomerization activity advantageously at low W loading (6–12 wt.%) compared to the micro-meter size ones. This finding corresponds to formation of poly-tungstate WO x species already at low loadings, likely at the defective sites of the nano-size zirconia.

Aviation fuel production from lipids by a single-step route using hierarchical mesoporous zeolites

Hierarchical mesoporous molecular sieves with tunable zeolitic crystallinity, acidity and porosity were tailored to develop a single-step process for hydroconversion of triglycerides and free fatty acids obtained from algae and Jatropha seeds. Ni-W catalyst supported on acidic zeolitic ZSM-5 support with hierarchical structure and intra-crystalline mesoporosity with composition similar to that for typical hydrocracking catalyst could yield 40–45% C9–C15 hydrocarbons and high isomerization selectivity (isomer/n-alkane, i/n ~ 2–6) from Jatropha oil. While Ni-Mo catalysts on the same support furnished 40–50% kerosene range hydrocarbons with i/n ~ 3–13. For algal oil feed hydroconversion using sulfided Ni-Mo catalyst supported on high surface area semi-crystalline ZSM-5, unexpectedly high yield of jet-fuel range hydrocarbons (77%) with moderately high isomerization selectivity (i/n = 2.5) could be obtained.

ChemInform Abstract: Synthesis, Characterization, and Catalytic Properties of Clean and Oxygen-Modified Tungsten Carbides

Abstract High surface area WC and β-W 2 C powders (30–100 m 2 g −1 ) were prepared by direct isothermal carburization of WO 3 and W 2 N in CH 4 -H 2 mixtures. After surface cleaning with H 2 , their surfaces are equilibrated with bulk stoichiometric carbides and free of polymeric carbon; they chemisorb 0.2–0.4 monolayers of CO and H. These carbides catalyze neopentane hydrogenolysis with high selectivity. Chemisorbed oxygen also inhibits hydrogenolysis rates and introduces surface sites for neopentane isomerization, a reaction that occurs only on Pt, Ir, and Au metals. Chemisorbed oxygen also inhibits hydrogenolysis of n-hexane and n-heptane on tungsten carbides and introduces surface sites that lead to high isomerization selectivity (70–99%). Kinetic and isotopic tracer studies of n-heptane, 3,3 dimethylpentane, methylcyclohexane, propylene, and methanol reactions show that dehydrogenation reactions and methyl-shifts of unsaturated intermediates occur on oxygen-modified WC powders. Carbidic sites (WC x ) catalyze C-H activation reactions; chemisorbed oxygen titrates such WC x sites and introduces Bronsted acid surface sites (WO x ). Thus, these materials catalyze both dehydrogenation and carbenium-ion reactions, reflecting the bifunctional nature of oxygen-modified transition metal carbide surfaces.

Effect of Hydrothermal Conditions on Isomerization Activity of Pt/SO<sub>4</sub><sup>2-</sup>-ZrO<sub>2</sub>

Pt/SO42--ZrO2 catalysts (PSZ) were prepared by using a series of hydrous zirconia as support synthesized via a hydrothermal method. The catalytic performances of these catalysts were evaluated in the n-hexane isomerization in a fixed bed reactor. The crystalline structure, acidity, reduction properties, textural texture, and sulfur content were characterized by XRD, NH3-TPD, H2-TPR, N2 adsorption and thermal analysis. The experimental results indicated that the hydrothermal ageing of zirconium hydroxide led to great changes in the crystalline structure of hydrous zirconia support, sulfur content, and the acidity of PSZ. The abundant strong acid sites and high sulfur content were essential but insufficient to achieve a PSZ catalyst with high isomerization activity. Too weak or too strong interaction between sulfur species and zirconia in the catalysts was unfavorable to the isomerization reaction. The presence of considerable sulfate species interacting moderately with zirconia was crucial to high isomerization activity.

WO 3 microcrystallites: One of the crucial factors controlling the isomerization activity of Pt/WO 3–ZrO 2

A series of hydrous zirconia supports were prepared by hydrothermal method and Pt/WO 3–ZrO 2 catalysts were prepared by impregnation method. The catalytic activity of Pt/WO 3–ZrO 2 in n-hexane isomerization was evaluated in a fixed-bed reactor. In order to investigate the crystalline structure, acidity, and textural properties, the catalysts were characterized by XRD and Raman spectroscopy, NH 3-TPD, FTIR, and N 2 adsorption. The results indicated that the crystalline structure of hydrous zirconia support and the state of tungsten oxide species over the catalyst varied obviously with the hydrothermal temperature, while no distinct change in the acidity of the catalyst occurred. The isomerization activity of Pt/WO 3–ZrO 2 could not well be correlated with the crystalline structure of hydrous zirconia support and the acidity. It was proposed that the presence of considerable microcrystalline WO 3 in catalyst was indispensable for achieving high isomerization activity.

Conversion of 1- and 2-Tetralone Over HY Zeolite

Conversion of 1- and 2-tetralone was investigated over acid HY zeolite under various reaction conditions in the vapor phase. Reactions were conducted in a fixed-bed reactor at 300, 400 and 500 °C in hydrogen atmospheric pressure. It was found that 1- and 2-tetralone are thermally unstable and thermal reaction has a contribution, particularly at high temperatures. The reactivity of 2-tetralone was significantly higher than that of 1-tetralone. This behavior is more pronounced in the presence of acid HY zeolite. For both isomers, the main products were naphthol, coupling compounds (4-ring), naphthalene and tetralin. Trace amounts of dihydronaphthalene, ring-contraction and ring-opening product were also observed. At high temperatures, isomerization and dehydration of naphthol were observed over the HY zeolite. It seems that on the acidic zeolite, hydrogen transfer plays a significant role in determining the reaction path. Thermal and catalytic conversion of 1- and 2-tetralone were investigated over HY zeolite. Tetralones are thermally unstable and 2-tetralone shows higher reactivity than 1-tetralone. This behavior is more pronounced in the presence of HY zeolite. Main products are naphthol, coupling compounds, naphthalene and tetralin. At high temperatures, isomerization and dehydration of naphthol were also observed over the HY zeolite.

Substrate specificity of a recombinant d-lyxose isomerase from Providencia stuartii for monosaccharides

The specific activity and catalytic efficiency (k(cat)/K(m)) of the recombinant putative protein from Providencia stuartii was the highest for D-lyxose among the aldose substrates, indicating that it is a D-lyxose isomerase. Gel filtration analysis suggested that the native enzyme is a dimer with a molecular mass of 44 kDa. The maximal activity for D-lyxose isomerization was observed at pH 7.5 and 45 degrees C in the presence of 1 mM Mn(2+). The enzyme exhibited high isomerization activity for aldose substrates with the C2 and C3 hydroxyl groups in the left-hand configuration, such as D-lyxose, D-mannose, L-ribose, D-talose, and L-allose (listed in decreasing order of activity). The enzyme exhibited the highest activity for D-xylulose among all pentoses and hexoses. Thus, D-lyxose was produced at 288 g/l from 500 g/l D-xylulose by D-lyxose isomerase at pH 7.5 and 45 degrees C for 2 h, with a conversion yield of 58% and a volumetric productivity of 144 g l(-1) h(-1). The observed k(cat)/K(m) (920 mM(-1) s(-1)) of P. stuartiid-lyxose isomerase for D-xylulose is higher than any of the k(cat)/K(m) values previously reported for sugar and sugar phosphate isomerases with monosaccharide substrates. These results suggest that the enzyme will be useful as an industrial producer of D-lyxose.

Alkyl substituted [6,6]-thienyl-C61-butyric acid methyl esters: easily accessible acceptor materials for bulk-heterojunction polymer solar cells

[6,6]-Thienyl-C61-butyric acid ester derivatives with methyl, hexyl and 2-ethylhexyl at the 5-position of thiophene ring (TCBM-Cn, n represents the number of carbon atom in the alkyl chain) were synthesized. Unlike [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), these methanofullerene derivatives ([6,6] adduct) can be directly obtained from the typical diazo addition under mild conditions, and high temperature isomerization is unnecessary. With a hexyl or 2-ethylhexyl group at the 5-position of thiophene, the solubility of TCBM-Cn in chlorobenzene is as high as 180 ± 10 mg ml−1. Bulk heterojunction photovoltaic solar cells were fabricated with a device structure of ITO/poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS)/poly(3-hexylthiophene) (P3HT) : TCBM-Cn (1 : 0.8 w/w)/LiF/Al. The device based-on TCBM-C6 exhibited the best performance with a power conversion efficiency (PCE) of up to 4.26%.

A High‐Barrier Molecular Balance for Studying Face‐to‐Face Arene–Arene Interactions in the Solid State and in Solution

An atropisomeric molecular balance was developed to study face-to-face arene-arene interactions. The balance has a large central 1,4,5,8-naphthalene diimide surface that forms intramolecular arene-arene interactions with two pendent arms. The balance adopts distinct syn and anti isomers with varying numbers of intramolecular interactions. Thus, the strength of the arene-arene interaction could be quantitatively measured by NMR spectroscopy from the anti/syn ratios. The size of the arene arms was easily varied, which allowed examination of the relationship between arene size and strength of the interaction. A nonlinear size dependence was observed in solution with larger arene arms having a disproportionately stronger arene-arene interaction. The intramolecular arene-arene interactions were also characterized in the solid state by X-ray crystallography. These studies were facilitated by the kinetic stability of the syn and anti isomers at room temperature due to the high isomerization barrier (DeltaG=27.0 kcal mol(-1)). Thus, the anti isomer could be selectively isolated and crystallized in its folded conformation. The X-ray structures confirmed that the anti isomers formed two strong intramolecular arene-arene interactions with face-to-face geometries. The solid-state structure analysis also reveals that the rigid framework may contribute to the observed nonlinear size trend. The acetate linker is slightly too long, which selectively destabilizes the balances with smaller arene arms. The larger arene arms are able to compensate for the longer linker and form effective intramolecular arene-arene interactions.

The synthesis and properties of novel, functional azobenzene based metal complexes

Azobenzene-containing metal complexes with different carbon chain lengths connecting the azobenzene moiety and the diamine ZnCl 2 unit were characterized using spectrophotometric methods as well as thermal and X-ray diffractometric analysis. The length of the chain between the azobenzene moiety and the diamine metal complex influences both the thermal and fluorescent behaviour of the bi-functional compounds. Combining the azobenzene chromophore with the metal complex results in remarkably high azobenzene isomerization as well as two-band fluorescence emission centered at 290 and 560 nm respectively, imparted by the metal complex component. A holographic image inscription and readout experiment of one of the metal complexes in a poly(methyl methacrylate) matrix is described.