Microwave-Driven Plasma-Mediated Methane Cracking: Product Carbon Characterization

Abstract

Methane is the primary industrial H2 source, with the vast majority produced by steam reforming of methane—a highly CO2- and water-intensive process. Alternatives to steam reforming, such as microwave-driven plasma-mediated methane decomposition, offer benefits of no water consumption and zero CO2 process emissions while also producing solid carbon formed by pyrolytic reactions and aided by a plasma reactive environment. The economic viability of pyrolytic methane decomposition as a hydrogen source will depend upon the commercial applications of the solid carbon product—which, in turn, will depend upon its physical and chemical characteristics. This study focuses on material characterization of the solid carbon (secondary) product. Characterization by high-resolution transmission electron microscopy reveals forms ranging from graphitic to amorphous. Thermogravimetric analyses reveal three forms by their differing oxidative reactivity, while X-ray diffraction analyses support the different crystalline forms as suggested by Thermogravimetric analysis. Plasma perturbation of the radical pool, elevating radical temperatures and boosting concentrations, is proposed as altering the reaction paths towards solid carbon formation, resulting in the different sp2 forms.