Kohji Omata

On the active site of MgO/CaO mixed oxide for oxidative coupling of methane

Abstract The catalytic performance of Mg/Ca mixed oxides for oxidative coupling of methane and their physical properties were studied. It was found that while the activity for formation of carbon oxides was not influenced by the ratio MgO/CaO, both selectivity and activity to CZ hydrocarbons were maximum (67% and 14.5 C-mmol · h−1 · g−1, respectively) with 85% MgO/CaO at 1023 K. The values increased with increasing reaction temperature. Physical properties such as the strain in the MgO lattice and the amount of strongly adsorbed CO2 were also maximum at the same composition. It was found that most of the surface species was MgO for Mg-rich oxides. Surface basicity, which was estimated by the wavenumber difference of the asymmetric and symmetric IR absorption bands of surface carbonates, was associated with these properties. The basicity of MgO, which was promoted by incorporated CaO, is considered to be the main factor for promoting the coupling activity.

Selective oxidative coupling of methane with membrane reactor

Membrane reactors for selective oxidation of methane to higher hydrocarbons were designed and successively operated. In this system, methane was converted by oxide ion supplied through the non-porous membrane film. Three types of membrane reactors were developed for the oxidative coupling of methane. The first one consists of a porous tube covered with a thin film of catalyst oxide (Type-I), the second one is a non-porous tube of solid ion conductor covered with a catalyst layer (Type-II), and the third one is a non-porous tube made of perovskite-type mixed conductor which itself has activity for methane conversion (Type-III). Type-I and II membranes converted methane to C2 hydrocarbons with the selectivity higher than 90%.

Hydrogen effects on nickel-catalyzed vapor-phase methanol carbonylation

The influence of hydrogen on the reaction orders of CO and methanol, with respect to the formation of acyl compounds, methane, and dimethyl ether, was investigated. Although hydrogen-promoted methane formation, experiments with deuterium and methanol-d{sub 1}(MeOD) clarified that the hydrogen of the methanol hydroxyl group is the exclusive hydrogen source of the CH{sub 4} formation and that this reaction occurs at nickel centers, which are also involved in the acyl compound formation. Temperature-programmed reaction (TPR) and X-ray diffraction (XRD) experiments suggested that the hydrogen effect is caused by changes in the number of active sites and that neither methanol carbonylation nor methane formation proceeds at the larger nickel(0) crystallites detectable by XRD. Furthermore, it has been demonstrated that under certain reaction conditions, hydrogen can induce a remarkable deactivation of the catalyst by promoting nickel aggregation. A mechanism that accounts for the hydrogen effects has been postulated.

Selective oxidative coupling of methane over supported alkaline earth metal halide catalysts

Abstract Halides of alkaline earth metals supported on calcium oxide or magnesium oxide were found to be excellent catalysts for the oxidative coupling of methane. For example, the selectivity with respect to C 2 hydrocarbons over a 5 wt.-% MgCl 2 /CaO catalyst reached 90% or higher with a yield of 10% at 750°C and CH 4 /O 2 =9. Although the selectivity with respect to C 2+ hydrocarbons gradually decreased with processing time, the in situ replenishment of the trace amount of halogen compound in the feed gas prevented this decrease. The halide ion in the catalyst is inferred to change the surface character of the alkaline earth metal oxide, reducing its ability for methane decomposition and resulting in suppression of the deep oxidation of methane.

Oxidative coupling of methane over CaO-MgO mixed oxide

Mixed oxide catalyst prepared by co-precipitating magnesium oxide and calcium oxide showed an excellent activity for the oxidative coupling of methane. The high performances were presumed to arise from the high basicity of the mixed oxide.

Selective synthesis of liquid hydrocarbons from carbon dioxide and methane

Abstract The synthesis of liquid hydrocarbons from carbon dioxide and methane was studied under pressurized conditions using two stage reactor process composed of methane reforming by CO2 and Fischer-Tropsch reaction. A nickel supported magnesia catalyst gave the equilibrium conversion of CH4 and CO2 above 850 °C. On a Co-La/SiO2 catalyst the CO conversion was 20 % at 250 °C and 0.7 MPa and the selectivity to C5+ hydrocarbon was 70%. The major by-product in the second reactor was CH4, which can be recycled into the first reforming reactor.

Vapor-phase carbonylation of methanol over lead on active carbon catalyst

Lead supported on active carbon showed a catalytic activity for the vapor phase carbonylation of methanol under pressurized conditions in the presence of methyl iodide promoter.

Preparation of nickel-on-active carbon catalyst by CVD method for methanol carbonylation

The nickel on active carbon (Ni/A.C.) catalysts prepared by a simple chemical vapor deposition (CVD) method showed comparable catalytic activities for the vapor phase carbonylation of methanol to those of the catalysts prepared by impregnating A.C. with nickel nitrate and activating by hydrogen treatment. The CVD method was successfully applied to the in situ catalyst preparation.

Methane partial oxidation to methanol-solid initiated homogeneous methane oxidation

The initiation temperature of methane partial oxidation was markedly lowered by platinum wire placed upstream of a high pressure reactor. Added hydrogen in the reactant gas promoted the methanol selectivity. The radicals formed on the platinum surface were desorbed from it and initiated the reaction.

Liquid phase carbonylation with solid catalyst Part 2. Carboxymethylation of bromobenzene with group VIII metals supported on active carbon

Abstract It was found that palladium supported on active carbon showed high catalytic activities and selectivities for the carbonylation of bromo- and iodobenzene to benzoic acid derivatives in the liquid phase. The carbonylation activity increased with the addition of water to the reaction solvent.