Microwave assisted heterogeneous catalysis: effects of varying oxygen concentrations on the oxidative coupling of methane

The oxidative coupling of methane was investigated over alumina supported La2O3/CeO2 catalysts under microwave dielectric heating conditions at different oxygen concentrations. It was observed that, at a given temperature using microwave heating, selectivities for both ethane and ethylene were notably higher when oxygen was absent than that in oxygen/methane mixtures. The differences were attributed to the localised heating of microwave radiation resulting in temperature inhomogeneity in the catalyst bed. A simplified model was used to estimate the temperature inhomogeneity; the temperature at the centre of the catalyst bed was 85 °C greater than that at the periphery when the catalyst was heated by microwaves in a gas mixture with an oxygen concentration of 12.5% (v/v), and the temperature difference was estimated to be 168 °C in the absence of oxygen

Catalysts for the utilization of methane from the coal mine ventilation air

The paper indicates coal mines as the source of permanent emission of low-concentrated gases, which have increased the greenhouse effect. This paper proposes the catalytic oxidation of methane as the solution to the problem of methane utilization when its concentration in the air is insufficient for flame combustion. The studies which have been conducted for many years enabled finding the active oxide and metallic catalytic systems for the reaction of methane oxidation. For the utilization of gases with low-concentrated methane, using the low-temperature catalysts, especially palladium catalysts, seems to he economically well-justified. Depending on technological solutions it can be considered as the method for methane utilization or as an environmentally friendly way for the generation of electric and thermal energy

Effect of the surface state on the catalytic performance of a Co CeO2 ethanol steam reforming catalyst

This work examines the impact of the Co/CeO₂ catalysts’ surface oxidation state and composition on the ethanol steam reforming (ESR) reaction performance. To this purpose, in situ and ex situ X-ray photoelectron spectroscopy (XPS) combined with on-line mass spectrometry were applied in a wide pressure range (0.2–20 mbar). When the reaction was performed at 0.2 mbar, metallic cobalt and partly reduced cerium oxide were found regardless of the catalysts’ pretreatment conditions. This surface state favors CO and H₂ production, indicating that Csingle bondC bond cleavage is the most important pathway in this pressure regime. A higher reduction degree of ceria gave rise to a larger population of adsorbed hydroxyl groups, which, contrary to the expected behavior, suppressed the activity and the Csingle bondC bond cleavage yield. Under higher pressure (4–20 mbar), gradual oxidation of cobalt and ceria was noted. The presence of ionic cobalt species appears to enhance CO₂ and acetaldehyde yields. On the basis of the present results and the available literature a plausible pressure-dependent reaction mechanism is proposed