Microwave-assisted pyrolysis of CH4/N2 mixtures over activated carbon

The aim of this work was to study the microwave-assisted pyrolysis of CH₄ over an activated carbon, which acted as both microwave receptor and catalyst, and the influence of using different CH₄/N₂ ratios on the conversion of CH₄ to H₂. In order to compare the results obtained in the microwave oven, the pyrolysis was also carried out under conventional heating (electric furnace, EF). The effects of N₂, which enhanced significantly CH₄ conversion, differed depending on the heating device used. Under EF heating, N₂ seemed to have an effect similar to distribute the CH₄ molecules within the activated carbon bed. Under microwave heating (MW), the N₂, as well as distributing the CH₄ molecules, favoured the generation of energetic microplasmas, leading to higher conversions. The prevalence of one role over the other depended on the CH₄/N₂ ratio, the appearance of energetic microplasmas being favoured with high percentages of N₂. Consequently, CH₄ conversion was higher at low CH₄/N₂ ratios. Additionally, the formation of carbon nanofibres in experiments where a combination of N₂ and MW heating was used is also reported.