Microwave Dielectric Heating Behavior of Supported MoS 2 and Pt Catalysts

Sun

et al. 2009

React Kinet Catal Lett

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The oxidative coupling of methane was investigated over alumina supported La 2 O 3 /CeO 2 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.

Section: Microwave Power Absorptionsupporting

confidence: 93%

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

Binghua

Sun

et al. 2009

React Kinet Catal Lett

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“…In work with an 8% MoS 2 /alumina catalyst [21], it was found that the fraction of the input power that was absorbed by the catalyst increased from 0.13 at 18 • C to 0.25 at 350 • C. The higher values reported here must be due to the greater loading of molybdenum sulfide (30%). This material has an effective dielectric loss factor of 0.85 at 200 • C [22], compared to 0.025 for alumina, and must be responsible for the major part of the heating.…”

Section: Microwave Power As a Function Of The Temperature Of Catalystmentioning

confidence: 56%

Microwave assisted catalytic reduction of sulfur dioxide with methane over MoS2 catalysts

Zhang

Hayward

Applied Catalysis B: Environmental

et al. 2001

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The catalytic reduction of sulfur dioxide with methane to form carbon dioxide and sulfur has been studied over MoS 2 /Al 2 O 3 catalysts. The reaction has been found to occur with microwave (2.45 GHz) heating at recorded temperatures as much as 200 • C lower than those required when conventional heating was used. An activation energy of 117 kJ mol −1 has been calculated for the conventionally heated reaction, but an Arrhenius analysis of the data obtained with microwave heating was not possible, probably because of temperature variations in the catalyst bed. The existence of hot spots in the catalysts heated by microwave radiation has been verified by the detection of ␣-alumina at a recorded temperature some 200 • C lower than the temperature at which the ␥-to ␣-alumina phase transition is normally observed. Among four catalysts prepared in different ways, a mechanically mixed catalyst showed the highest conversion of SO 2 and CH 4 for microwave heating at a given temperature. Supported catalysts, sulfided either by conventional heating or under microwave conditions, showed little difference in the extent of SO 2 and CH 4 conversions. The highest conversions to carbon dioxide and sulfur, combined with low production of undesirable side products, was obtained when the molar ratio of SO 2 to CH 4 was equal to two, the stoichiometric ratio.

“…The much lower temperature measured when microwave radiation is used must arise from temperature gradients within the catalyst. These temperature gradients will cause localised heating of the gaseous reactants because of the high rate of heat transfer between the internal surface of the catalyst and the gas phase, as investigated in our earlier work [32]. Fig.…”

Section: Reaction Of Methane In Absence Of Oxygen Without Catalystmentioning

confidence: 87%

“…This indicated an increase in microwave heating efficiency at higher temperatures, and may be attributed to the increase in the dielectric loss of the catalyst with increasing temperature [32].…”

Section: Microwave Power As a Function Of The Temperature Of Catalystmentioning

confidence: 94%

Oxidative coupling of methane using microwave dielectric heating

Zhang

Applied Catalysis A: General

Mingos

et al. 2003

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Microwave heating was applied in the oxidative coupling of methane to higher hydrocarbons over alumina supported La 2 O 3 /CeO 2 catalysts. It was found that microwave heating had a dramatic effect on the reaction when methane was converted into C 2 hydrocarbons in the absence of oxygen, with products produced at measured temperatures about 250 • C lower than those observed with conventional heating. It was shown that the reaction in the absence of oxygen occurred primarily in the gas phase and it was the localised heating of the methane that was responsible for the increased reaction rate. However, it was observed that microwave heating did not produce significant "special microwave effects" which affected the product species formed when the oxidative coupling reaction occurred in the presence of oxygen.