Applications of microwave dielectric heating in environment-related heterogeneous gas-phase catalytic systems

Abstract

The application of microwave dielectric heating in a range of environment-related heterogeneous catalytic reaction systems has been reviewed. The reactions investigated include the decomposition of hydrogen sulfide, the reduction of sulfur dioxide with methane, the reformation of methane by carbon dioxide, the hydrodesulfurization of thiophene, and the oxidative coupling of methane. The interaction of microwave irradiation with heterogeneous catalytic systems and its consequence for the microwave heating behaviour of catalysts have been examined. The effect/mechanism of microwave dielectric heating on heterogeneous catalytic reaction systems has also been discussed.

Pulsed activation in heterogeneous catalysis

“…Not all materials in the reactor are equally susceptible to microwaves, leading to the creation of mesoscopic hot-spots. These hot-spots can be up to 200 K warmer than their immediate surroundings [128]. The fact that it is difficult to apply a homogeneous microwave field further enhances localized thermal gradients.…”

“…Many of the reactions for which the microwave assisted chemistry produces good results are endothermic [34,128,145], or at least have a very high activation barrier. Since endothermic reactions actually absorb heat, efficient application of energy at the place of reaction gives higher local temperature at the same input of overal heat leading to lower overal losses to the surroundings.…”

Energy consumption estimation in the scaling-up of microwave heating processes

“…These include: (i) non-contact heating; (ii) rapid heating; (iii) selective heating; (iv) a quick start/stop facility; (v) a high level of safety and automation; and (vi) heating from inside the body of the material (i.e., energy conversion instead of heat transfer) [1,3]. All of these advantages have promoted research into the application of microwave heating to a wide range of different processes including waste and biomass valorization [4], material synthesis [5,6], metallurgy and mineral processing [3,7], catalysis [8], organic synthesis [9], environmental technology [7,10], biomass extraction [11], etc.…”

Microwave-induced nanoscale zero-valent iron degradation of perchloroethylene and pentachlorophenol

“…Equation 1 shows that " 00 eff plays an important role in the MW energy absorption equation. The temperature rise of the medium absorbing MW energy can be expressed by the following equation (Clark et al, 2000;Zhang et al, 2006):…”