Method for hydrogen production by methane cracking using vacuum plasma

Abstract

Methane cracking is highly attractive as it can produce hydrogen gas and carbon-based materials without directly generating carbon dioxide. However, most methane reforming processes require high temperatures (over 600 °C) while catalyst materials are integrated. To address this challenge, in this work, the $C{H}_4$cracking using a low-pressure RF plasma system is studied to analyze the produced molecular hydrogen and carbon-based products. Mass Spectrometry (MS) and Optical Emission Spectroscopy (OES) were used to identify the key species such as hydrogen ($H_2$), CH radicals, and $C_2$ hydrocarbons. Additionally, X-Ray Photoelectron Spectroscopy (XPS) is used to examine carbon deposits within the RF plasma reactor. Moreover, the OES spectra revealed distinct emission peaks for $H_{\alpha }$, $H_{\beta }$, CH radicals, and $C_2$ Swan bands, while quadrupole mass spectroscopy confirmed the production of hydrogen molecules. The results obtained show that the effective methane dissociation occurs alongside solid carbon formation within the plasma deposition system. Besides, using the XPS technique, the deposited carbon was identified as hydrogenated amorphous carbon (a-C: H), containing both sp² and sp³ hybridized carbon atoms. Furthermore, it was observed that higher RF input power significantly enhances plasma density, electron temperature, and $C{H}_4$conversion efficiency, with a peak performance at 300 W before reaching a saturation situation. These saturation effects are due to the space charge phenomena and energy distribution towards other processes such as dissociation and ionization.