Catalytic Activity For Oxidative Coupling Research Articles

Effect of pressure on the phase composition of Li(Na)/W/Mn/SiO2 composites and their catalytic activity for oxidative coupling of methane

The phase state of Li/W/Mn/SiO2 and Na/W/Mn/SiO2 composites after exposure to high pressures (2.5 GPa at 500°C) and subsequent exploitation in oxidative coupling of methane (OCM) was studied. Comparison of the catalytic activity of the composites before and after exposure to high pressures indicates that the formation of Li(Na)/W/Mn/SiO2 composites catalytically active for OCM is significantly influenced by high pressures.

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.

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.

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

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.

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.

Bond Energy Effects in Methane Oxidative Coupling on Pyrochlore Structures

Compounds of general formula A2B2O7 have been characterized by X-ray diffraction and tested for catalytic activity in oxidative coupling of methane. Calculations of the rare earth-oxygen (AO) and cocation-oxygen (BO) bond energies provide a new way to estimate the influence of bulk parameters on the formation of C2 hydrocarbons. The observed values of C2 yields on A2B2O7 catalysts (A = Sm, Gd or Eu) (B = Ti, Zr, or Sn) indicate that they increase with decreasing cocation-oxygen bond energy. The best of these systems (Sm2Sn2O7) gives a C2 yield amounting to 20% at 973 K.

FTIR spectroscopic study of carbon dioxide adsorption/desorption on magnesia/calcium oxide catalysts

The nature of adsorption states of CO{sub 2} on mixed Mg/Ca oxide catalysts was investigated by FTIR spectroscopy. At room temperature, the unidentate is predominantly formed besides bicarbonate. On CaO-rich catalysts additional structures were detected and attributed to bridging carbonate and linearly adsorbed CO{sub 2}. Desorption behavior of these species is discussed in dependence on temperature. Surface basicity was quantitatively measured by the wavenumber difference of symmetric and asymmetric carbonate absorption bands and related to catalytic activity for oxidative coupling of methane. 22 refs., 6 figs., 2 tabs.

Influence of basicity on the catalytic activity for oxidative coupling of methane

Basicity is shown to be a fundamental catalytic property of the alkaline earths and the rare-earths oxide (REO) catalysts to promote the oxidative coupling reaction of methane (OXCO). The basicity was measured by thermogravimetry from the decomposition temperatures of the carbonates. At an OXCO reaction temperature that allows at least part of the catalyst to be in the oxide form, the C 2+ selectivity is directly proportional to the basicity of the alkaline earth oxide catalysts. A similar basicity-C 2+ selectivity relationship can also be seen among the REO's. The difference in basicity between two REO's is not as great as the alkaline earth oxides, nor does basicity change uniformly across the periodic table. Moreover, the REO's contain sites of various basic strengths. Some of these sites are active for OXCO reaction through the rupture of C-H bond whereas others promote deep oxidation of the product hydrocarbons, giving rise to a low apparent selectivity.

Acidity/basicity of rare-earth oxides and their catalytic activity in oxidative coupling of methane to C 2-hydrocarbons

Rare-earth metal oxides (viz. La 20 3, Ce0 2, Sm 20 3, Eu 20 3, and Yb 20 3) have been compared for their acid and base strength distribution (measured by stepwise thermal desorption of C02 from 323 to 1173 K and TPD of NH 3 from 323 to 1223 K, respectively) and their catalytic activity/ selectivity in oxidative coupling of methane to C2-hydrocarbons at 973–1123 K (space velocity = 108,000 cm 3 · g −1 h −1 and CH 4/O 2 = 4 and 8). The catalyst activity and selectivity showed dependence on both the surface acidity and basicity. However, the relationship of the catalytic activity/ selectivity with the surface acidity /basicity is not straightforward; it is quite complex. Stronger acid sites are found to be harmful for the selectivity. There is a possibility of an involvement of an acid-base pair (M LC n+i c 0 LC 2− , where subscript LC denotes low coordination) on the surface in the abstraction of the H-atom from adsorbed methane molecule by its polarization followed by heterolytic C-H bond rupture to form CH 3 − (which interacts with M LC n+ .c) and (OH) LC − and a transfer of electron from the carbanion to O 2, resulting methyl radical and O z. Regeneration of basic sites and the possibility of formation of 0 − species on the catalyst surface are discussed.

Methane Oxidation over Perovskite-type Oxide Containing Alkaline-earth Metal

Abstract Perovskite-type oxides(ABO3) containing alkaline-earth metal Ba or Sr exhibited fairly good catalytic activity for oxidative coupling of methane to ethane and ethylene. These oxides were stable against produced carbon dioxide at 1023 K. The catalytic activity was well correlated with the A ion and the difference of the interatomic distance from the equilibrium distance.

Catalytic activity of supported palladium catalysts with different dispersities in the hydrogenation and oxidative coupling of styrene

The effect of dispersity of supported palladium catalysts on the catalytic activity for hydrogenation and oxidative coupling of styrene has been studied. Changes in the catalytic activity for oxidative coupling are interpreted in terms of the dependence of oxygen adsorption on metal dispersity.