Takakazu Fukushima

Oxidative coupling of methane over Y2O3CaO catalysts

Abstract Binary oxides of Y 2 O 3 CaO were evaluated as catalysts in the oxidative coupling of methane to C 2+ (sum of C 2 H 6 , C 2 H 4 , C 3 H 8 , and C 3 H 6 ) hydrocarbons. Passing a mixture of CH 4 /O 2 and He gases (at 6, 3 and 31 ml/min respectively) in a fixed-bed flow reactor 13% and 7.5% of C 2+ yields were achieved at 750°C and 650°C, respectively, over 0.5 g of 10 mol-% Y 2 O 3 CaO catalyst prepared by calcining a coprecipitate of their oxalates at 800°C. The C 2+ yields on 10 mol-% Y 2 O 3 CaO, prepared by physical mixing, were lower than those on the coprecipitated catalyst. With increasing Y 2 O 3 content in the coprecipitated catalyst, the C 2+ selectivity at 700°C was significantly enhanced even at ca. 3 mol-%, whereas at 600°C such a change was not observed. A similar dependence on the Y 2 O 3 content was found in the way both surface areas and basicities decreased. Those changes were attributed to the formation of a solid solution accompanying the production of interstitial oxygen ions. Electron-spin resonance (ESR) studies indicated that the ion is a superoxide ion which is responsible for the generation of methyl radical from methane. At low reaction temperatures, 700°C, it was found that a lattice distortion of Y 2 O 3 in the binary oxides also affected the C 2+ selectivity.

Mechanism of syngas conversion into C2-oxygenates such as ethanol catalysed on a SiO2-supported Rh–Ti catalyst

13 C-Labelling studies on a Rh–Ti/SiO2 catalyst using 13CO and 13CH3OH revealed that in a CO–H2 reaction C2-oxygenates such as ethanol are formed from a common precursor e.g. acyl, being formed by CO insertion onto surface CH3/CH2 moieties derived from CO dissociation and the subsequent reaction of the carbon product with hydrogen.

High-pressure i.r. spectroscopic evidence of acetyl and acetate species directly formed in CO–H2 conversion on SiO2-supported Rh and Rh–Mn catalysts

By in situ high-pressure i.r. spectroscopy acetyl [MeCO] as a possible intermediate for C2-oxygenates and acetate surface species are observed over Rh/SiO2 and Rh–Mn/SiO2 catalysts in a CO–H2 reaction (CO/H2= 0.5, 30–50 kg/cm2, 230–270 °C).

Characterization of silica supported Rh-Fe catalysts by Mössbauer technique

Silica supported Rh−Fe catalysts were characterized by means of in situ57Fe Mössbauer spectroscopy. The Mössbauer spectra indicated that iron on the silica support existed either as Fe/O/ in the Rh−Fe alloy or as Fe3+ in Rh−Fe metal cluster compounds. The (Fe3+/Fe/O/) ratio and Mössbauer parameters were found to depend on the (Fe/Rh) atomic ratio in the catalysts. Such dependence corresponded to the change of catalytic properties of the supported Rh−Fe catalyst with the varying (Fe/Rh) ratio.

Oxidative methylation of toluene with methane over alkali-promoted Y2O3–CaO catalysts

The Y2O3–CaO catalyst system, which is active for the oxidative coupling of methane to form C2 hydrocarbons, catalysed the oxidative methylation of toluene using methane as the methylene source, to give ethylbenzene and styrene; the addition of alkali metal oxide greatly improved the selectivity in the order:Li2O > Na2O > K2O.

Highly selective synthesis of C2-oxygenates in CO hydrogenation on SiO2-supported Rh–lr and Rh–Ti–lr catalysts

The addition of Ir to Rh/SiO2 and Rh-Ti/SiO2 CO hydrogenation catalysts substantially suppresses methanation and enhances C2-oxygenate formation; consequently high selectivities for C2-oxygenates such as MeCHO and EtOH are achieved.

Structures of teh catalysts derived from Rh–Co bimetallic carbonyls supported on γ-Al2O3: study of Rh-K EXAFS

It is revealed from the analysis of Rh-K EXAFS data that, in the catalysts derived from Rh2Co2(CO)12 and RhCo3(CO)12 supported on γ-Al2O3, metal atoms are present as bimetallic clusters similar to the ones which originally exist in the carbonyl molecules, whereas relatively large Rh–Co alloy particles are formed in the case of the catalysts prepared by the co-impregnation of RhCl3 and CoCl2.

Promoting role of Fe in enhancing activity and selectivity of MeOH production from CO and H2 catalysed by SiO2-supported Ir

Addition of Fe to Ir/SiO2 catalysts used in CO hydrogenation improves the yield of and selectivity towards MeOH (90% carbon efficiency), owing to suppression of methanation.

Selective synthesis of ethylbenzene and styrene by cross-coupling between toluene and methane over a lithium-promoted Y2O3–CaO catalyst

Isotope-labelling experiments have shown that toluene oxidative methylation using methane to form C8 hydrocarbons over a lithium promoted Y2O3–CaO catalyst involves a cross-coupling between the methyl and benzyl radicals on the surface.

A Mössbauer study on remarkable changes in chemical states of iron in silica-supported Pd-Fe bimetallic catalysts by varying Fe contents

Fe-57 Mössbauer spectra of silica-supported Pd−Fe bimetallic catalysts show remarkable changes with varying Fe/Pd atomic ratios. From the spectra, the main Fe-component is estimated as highly dispersed Fe in the Fe/Pd range of 0.05–0.3 and α-Fe ensemble and Fe−Pd intermetallics in the Fe/Pd range above 0.3. It is suggested that the chemical state of iron is associated with the catalytic performance in effective CO−H2 conversion to methanol.