Activity For Oxidative Coupling Research Articles

Nickel-doped zinc aluminate oxides: starch-assisted synthesis, structural, optical properties, and their catalytic activity in oxidative coupling of methane

Nanosized nickel-substituted zinc aluminate oxides were obtained by the gradual insertion of nickel cations within the zinc aluminate lattice, using starch as active ingredient. The obtained (Ni x Zn1−x Al2)-starch (x = 0.1, 0.2, 0.4, 0.6, 0.8, 1) gel precursors were characterized through infrared spectroscopy and thermal analysis. The thermal behavior of the precursors are influenced by the nickel content, the DTA curves for the richer nickel samples revealing stronger, faster and overlapping exothermic reactions, that can be completed at lower temperatures. The corresponding spinelic oxides were obtained after calcination treatments at 800 °C and analyzed by means of NIR–UV–Vis spectroscopy, XRD measurements, SEM, TEM, and HRTEM investigations. The spinelic structure for all oxide samples is confirmed by XRD analysis, although small amounts of NiO cannot be neglected. TEM/HRTEM analysis revealed mesopores embedded in plate-like large (68.8 nm) particles of Ni0.2Zn0.8Al2O4 sample and smaller (15.7 nm) uniform equiaxial particles, with a more pronounced tendency of agglomeration for Ni0.8Zn0.2Al2O4 oxide. A formation mechanism for Ni0.2Zn0.8Al2O4 oxides was proposed based on DTA/TG, XRD, and SEM analyses. NIR–UV–Vis spectra for Ni x Zn1−x Al2O4 showed a significant presence of tetrahedral nickel cations that augments with nickel concentration increase. CIE-L * a * b * color parameters shown a variation of the lightness and also of the green and blue color components with x, the best color characteristics being obtained for x = 0.6. The oxides with a substitution degree x = 0.2 and 0.8 tested in the oxidative coupled of methane reaction (OCM) showed positive catalytic activity and selectivity due to an interesting synergetic effect of Zn(II) and Ni(II) ions.

An ultra-low Pd loading nanocatalyst with high activity and stability for CO oxidative coupling to dimethyl oxalate

A Pd/α-Al2O3 nanocatalyst with ultra-low Pd loading exhibits high activity and stability for CO oxidative coupling to dimethyl oxalate, which was prepared by a Cu(2+)-assisted in situ reduction method at room temperature. The small size and high dispersion of Pd nanoparticles facilitated by Cu(2+) ions are responsible for the excellent catalytic activity.

Porous single-crystalline CdS nanosheets as efficient visible light catalysts for aerobic oxidative coupling of amines to imines

Porous single-crystal-like CdS nanosheets fabricated through a facile cation-exchange strategy exhibit a noticeable photocatalytic activity for aerobic oxidative coupling of amines to imines with 1 atm O2 under visible-light irradiation (λ > 420 nm) at room temperature.

Oxidative Coupling of Methane over Ba-incorporated LaInO<sub>3</sub> Perovskite Catalyst

We found that LaInO3 perovskite catalyst showed high activity for oxidative coupling of methane (OCM). Partial substitution of La3+ site in the LaInO3 catalyst with Ba2+ increased its catalytic activity and selectivity to C2 hydrocarbons drastically. The partial substitution of La3+ site in LaInO3 with Ba2+ increased oxygen vacancies in the stable cubic phase, and then contributed to the production of active oxygen species on its surface for selective C2 formation.

The promoting effect of ceria on Li/MgO catalysts for the oxidative coupling of methane

The effects of ceria loading (0.1–6.0 wt%) on the properties of Li/MgO catalysts and on their activities for oxidative coupling of methane (OCM) were studied. The catalysts were characterised by surface area measurement, XRD, XPS, SEM and CO 2 temperature programmed desorption. The catalyst activity study suggested that the addition of 0.5–1.0 wt% ceria improved the methane conversion of Li/MgO catalyst significantly at reaction temperatures below 800 °C with little change in C 2 selectivity compared to un-promoted Li/MgO. Further increases in ceria loading resulted in lower methane conversion and C 2 selectivity. The CH 4 conversion was related to the surface distribution of O − and O 2− on the catalysts. An increase in reaction temperature beyond 800 °C or a decrease in CH 4:O 2 ratio from 7:1 to 3:1 imparted negative effects on the methane conversion and C 2 selectivity of the ceria (0.5 wt%) doped Li/MgO catalyst. All ceria doped catalysts did not show any methane coupling activity in the absence of gaseous oxygen, suggesting that they were ineffective to work with alternate feeds of CH 4 and O 2 (redox) mode. Based on the OCM activity and characterisation results, a new pathway that describes the formation of active sites through the electron transfer between Ce 4+/Ce 3+and Li/MgO was proposed to help explain the improved OCM activity by using ceria doped Li/MgO catalysts.

Microemulsion-Aided Synthesis of Nanosized Perovskite-Type SrCoOx Catalysts

Nanostructured perovskite-type SrCoOx catalysts were prepared using a w/o-microemulsion as a soft template. Conventional co-precipitation and citric acid sol–gel were used as reference methods with regard to surface and bulk physico-chemical properties as well as catalytic performance in methane oxidation. The solids were characterised by XRD, SEM, TEM, EDX, N2-physisorption, TG-DTA-MS, ICP-OES, and H2-TPR techniques. The phase transformation temperature of the microemulsion-templated perovskites is by 150 K lower than that in the conventionally prepared ones. Therefore, this material is characterized by smaller crystallite sizes and higher surface areas. As result, it shows a higher activity in oxidative coupling of methane as compared to sol–gel and co-precipitated catalysts. The properties of the catalysts are weakly influenced by changing the specific synthesis parameters of the microemulsions.

One-Pot Preparation of Chiral Dinuclear Vanadium(V) Complex

A convenient one-pot procedure for the preparation of dinuclear vanadium(V) complex is described. The complex exhibited high catalytic activity for oxidative coupling of 2-naphthol derivatives. In addition, coupling of 9-phenanthrol gave (S)-10,10′-dihydroxy-9,9′-biphenanthryl in quantitative yield with 93% ee.

Silymarin synthesis and degradation by peroxidases of cell suspension cultures of Silybum marianum

Treatment of Silybum marianum cell cultures with methyl jasmonate elicits the production of the antihepatotoxic drug silymarin and its release into the culture medium. In this work, we investigated the involvement of peroxidases (EC 1.11.1.7; donor hydrogen peroxidase oxido-reductase) in silymarin turnover in cell cultures as well as the influence of elicitation on the activity towards several substrates. Peroxidases from cell extracts and, to a higher degree from the spent medium, used the silymarin precursors taxifolin and coniferyl alcohol as substrates. Silymarin compounds were also degraded by suspension culture peroxidases; however, the oxidation efficiency was not modified by elicitation. S. marianum peroxidases were able to catalyse the oxidative coupling of taxifolin and coniferyl alcohol to silybinins. The synthetic activity was mainly associated with the extracellular compartment and as before, methyl jasmonate did not modify oxidative coupling activity. Changes in the isoenzyme profiles were not observed in elicited cultures.

Isolation of a thermostable laccase with DMAB and MBTH oxidative coupling activity from a mesophilic white rot fungus

Carpophores of mesophilic basidiomycetes were isolated from the Eastern Cape region of South Africa. These isolates were screened for manganese peroxidase and laccase with high temperature optima. This bio-prospecting has led to the discovery of a thermostable laccase, which exhibits an optimum temperature of 70 °C. The enzyme remains fully active after 9 h incubation at 60 °C. The laccase is also capable of catalyzing the oxidative coupling of 3-dimethylaminobenzoic acid and 3-methyl-2-benzothiazolinone hydrazone, which are characterized as manganese peroxidase specific substrates. The wide temperature range, thermostability, and potentially wider than usual substrate range, make this an excellent candidate enzyme for industrial application.

Further evidence of responsibility of impurities in MgO for variability in its basicity and catalytic performance in oxidative coupling of methane

Further evidence was delivered that certain impurities, which could be contained in MgO samples, might be responsible for observed variability in MgO basicity and catalytic performance in oxidative coupling of methane. The surface basicity/base strength distribution of a series of MgO samples containing or not containing Ca and Na impurities was determined by a temperature-programmed desorption of CO 2. It was revealed that samples containing Ca and Na impurities have much more medium, strong and very strong basic sites. The surface basicity of MgO samples containing added alkali or alkaline earth compounds or water was characterized by a test reaction of transformation of 2-butanol. It was confirmed that the introduction of these compounds to a pure MgO enhanced both its basicity and activity in oxidative coupling of methane.

Influence of support on surface basicity and catalytic activity in oxidative coupling of methane of Li-MgO deposited on different commercial catalyst carriers

Deposition of Li-MgO catalyst on commonly used supports (containing SiO 2 , Al 2 O 3 , SiC, ZrO 2 , HfO 2 , etc.) causes a drastic reduction in the catalytic activity/selectivity for the oxidative methane coupling reaction and also in both the total and strong surface basicity. The decrease in the catalytic activity/selectivity and basicity is attributed to strong chemical interactions between the catalyst and support which occur during the high temperature (750°C) calcination/pretreatment of the catalyst. The chemical interactions result in catalytically less active binary and ternary metal oxides containing Li and/or Mg, thus deactivating the Li-MgO catalyst by consuming its active components.

Influence of support on surface basicity and catalytic activity in oxidative coupling of methane of Li–MgO deposited on different commercial catalyst carriers

Influence of support on surface basicity and catalytic activity in oxidative coupling of methane of Li–MgO deposited on different commercial catalyst carriers

Surface Praseodymium Species on MgO: Characterization and Activity for Oxidative Coupling of Methane

On pulsing CH4 over MgO containing various amounts of praseodymium oxide (PrOx) at 1023 K, the CH4 conversion decreased with increasing pulse number, and both the initial activity and selectivity to C2 products (corresponding to the first pulse) decreased with increasing PrOx content. Characterization by XRD, SEM-EDX and XPS showed calcined materials to contain well-dispersed PrOx (x = 1·83–2) at low Pr concentrations, but only crystalline PrO1·83 at high (10 wt%) Pr concentration. A PrO1·83 phase was present at all Pr concentrations after the He treatment at 1023 K, and PrO1·83, PrO1·75 and PrO1·5 after reaction. © 1997 SCI

Conductivity properties of Na2SO4/CaCO3 catalysts and their effect on catalytic activities for oxidative coupling of methane

A series of Na2SO4 doped CaCO3 catalysts were prepared. It was observed that the C2 yields and selectivities of Na2SO4/CaCO3 catalysts for OCM are intimately related to their conductivities. The effect of conductivity on the catalytic activity is discussed together with the conductivities and catalytic activities of the catalysts. The higher the conductivities, the higher the C2 yields and selectivities are.

BaCO3-supported vanadium oxide catalysts for the oxidative coupling of methane

BaCO3-supported vanadium oxide catalysts, which consist of BaCO3 and small amounts of a barium orthovanadate Ba3(VO4)2 phase, exhibit high catalytic activity for oxidative coupling of methane, with particularly high activity for ethene and ethane production.

Relationship Between Structure of LaxTh1-xO2-δMixed Oxide Catalysts and Catalytic Activity for Methane Oxidative Coupling

Relationship Between Structure of LaxTh1-xO2-δMixed Oxide Catalysts and Catalytic Activity for Methane Oxidative Coupling

Basic sites on the surface of oxide catalysts responsible for oxidative methane coupling

AbstractThe basic sites of various oxide catalysts for the oxidative dimerisation of methane were studied by FTIR spectroscopy of adsorbed molecular probes (chloroform and CO2). The methods used are compared and the advantage of CO2 as probe for specifying the basic sites is demonstrated. The strengths of the basic sites were seen to correlate with the spectral parameters of the surface carbonates. Differences in spectral responses of carbonates are attributed to the different states of oxygen participating in their formation. The concentration of the strongest sites was estimated. A study of the catalytic activity of this system indicates that the system's activity in oxidative methane coupling depends on the presence and concentration of strong basic sites on the catalyst surface.

Secondary ion mass spectrometry and X-ray photoelectron spectroscopy of Na2MoO4/SiO2 catalysts for methane oxidative coupling

A series of Na2MoO4/SiO2 catalysts with various loadings of Na2MoO4 have been characterized using secondary ion mass spectrometry (SIMS), X-ray photoelectron spectroscopy (XPS), FTIR and X-ray diffraction (XRD). Their catalytic activity for methane oxidative coupling (MOC) has been tested. The results revealed some type of interaction between Na2MoO4 and SiO2, which leads to a high dispersion of NaMoO4 at the support surface. The highly dispersed species covering the catalyst surface favour the formation of surface sites of low coordination. The relationship between catalytic performance and the amount of surface sites of low coordination was discussed.

Investigation of the catalytic performance of MgO/ BaCO 3 catalyst for the oxidative coupling of methane

Studies on bi-alkaline earth composite catalysts indicate that these new catalytic systems have high activity and selectivity for methane oxidative coupling. Of the above-mentioned catalysts, MgO/BaCO 3 composite catalyst possesses the highest activity and selectivity. In a comparison of single component samples with the MgO/BaCO 3 catalyst, it is shown that there is considerable interaction between the two components in the catalyst. The interaction leads the MgO/BaCO 3 catalyst to have the correct O 2 2− ion concentration and their distribution, lower lattice oxygen mobility, strong basicity of surface and lower specific surface areas to favor OCM. A C 2 yield of 16.3% and selectivity of 68% was obtained at 1053 K, CK 4/air = 1, GHSV = 3.88 × 10 4 h − over 0.25 g 62 mol% MgO/BaCO 3 catalyst during a 530 h stability test. Studies of the reaction conditions indicate that a C 2, yield higher than 18% could be obtained under properly selected reaction conditions. Experiments using a 26.4-mm diameter fixed-bed reactor with 10 ml MgO/BaCO 3 catalyst show that a C 2 yield of 16.3% and a C 2 selectivity of 65% was obtained with a catalyst bed temperature of ca. 1200 K, CH 4/O 2 = 5 and methane GHSV = 5000 h −1 with 1.8 ml/min water as a diluent.

Influence of Precursors Used in Preparation of MgO on Its Surface Properties and Catalytic Activity in Oxidative Coupling of Methane

Surface properties (viz., acidity/acid strength distribution, basicity/base strength distribution, surface area, morphology, and surface composition) and catalytic activity/selectivity in the oxidative coupling of methane at different process conditions [reaction temperature, 700-800°C; CH 4/O 2 ratio, 3.0-8.0; and gas hourly space velocity (GHSV), 25,500-102,000 cm 3 · g −1 · h −1)] of MgO obtained by thermal decomposition of hydrated MgO, magnesium hydroxide, magnesium nitrate, magnesium acetate, and magnesium carbonate have been investigated. The surface and catalytic properties are found to be strongly affected by the precursors used in the preparation of MgO. The catalytic activity and selectivity (for ethane and ethylene) of MgO obtained from magnesium carbonate and magnesium acetate are comparable and are much higher than that observed for MgO obtained from the other precursors.