Rate oscillations during partial oxidation of methane over chromel–alumel thermocouples

A chromel–alumel thermocouple has been found to catalyse the methane/oxygen reaction, the main products being CO, H2 with some CO2 and H2O. Regular oscillations in both reactants, products and temperature have been observed at temperatures around 700thinspcirC. Similar behaviour has been obtained using nickel wires

Microwave dielectric heating behaviour of supported MoS2 and Pt catalysts

The temperature of supported MoS2 and Pt catalysts was measured during microwave heating at constant input power by inserting a thermocouple into the center of the catalyst bed immediately after the microwave power had been turned off at the end of progressively longer heating times. Thermal runaway was observed with MoS2/Al2O3 and Pt/Al2O3 at temperatures in the range 285-300 C when the power absorbed rose with temperature at a rate greater than that at which heat is lost by cooling. This condition was not attained with MoS2/SiO2, and thermal runaway was not observed. For the MoS2 catalysts, the fraction of the microwave power absorbed, , was found to vary with temperature according to the equation = cA + cM exp(-Ea/RT), where cA and cM are constants and the activation energy, Ea, is 9.3 kJ mol-1 for MoS2/Al2O3 and 11.1 kJ mol-1 for MoS2/SiO2

Oscillatory behaviour during the partial oxidation of methane over nickel foils

The study of the partial oxidation of methane over nickel foils has been carried out over a wide range of reactor temperatures (748-930 °C) and feed-gas compositions (Ar/CH4/O2), ranging from 30:29:1 to 30:12:18 cm3 min-1 at atmospheric pressure. The product formation shows pronounced oscillations. A modified thermocouple was designed to measure the temperature while the interposed nickel foil worked as a catalyst. The oscillations have been attributed to the cyclic reduction and oxidation of the nickel surface in the specific reaction environment at elevated temperatures

Dielectric properties of MoS2 and Pt catalysts: effects of temperature and microwave frequency

The effects of temperature and microwave frequency on the dielectric properties of MoS2 and Pt catalysts together with an aluminum oxide support were investigated. Dielectric constants and dielectric loss factors were measured in a temperature range of 200-800 °C by a cavity resonator technique with a cylindrical copper cavity resonating in TM0n0 modes (n = 1, 2, ... ,5), which corresponded to frequencies of 0.615, 1.413, 2.216, 3.020, and 3.825 GHz

Oscillatory behaviour during the oxidation of methane over palladium metal catalysts

Oscillatory reactions over palladium foil and wire catalysts during the oxidation of methane have been investigated over a wide range of reaction temperatures and argon/methane/oxygen feed gas compositions. Characterisation of the catalyst has also been carried out using scanning electron microscopy (SEM) techniques, which revealed the presence of a porous surface. This suggested that the metal surface has undergone a change since the reaction commenced, and using X-ray powder diffraction (XRD) techniques the palladium phase was shown to be the dominant phase present. Hysteresis phenomena were observed in the activity of the reaction as the temperature was cycled up and down, showing that the metal surface was continually changing throughout the reaction. The activation energies of the reaction during the high reactivity mode, PdO, and low reactivity mode, Pd, were also calculated. Oscillation rates were observed to depend on the dominant surface. Oscillations were frequent when the high reactivity mode was dominant while the activation energy of this mode was found to be low. When the low reactivity mode was dominant, the oscillations were slower and the activation energy was three times larger. The results obtained imply that the behaviour of the palladium surface, switching back and forth from the reduced state to the oxidised state, is responsible for the oscillatory behaviour seen in this system