Steam reforming of n-hexane and toluene: Understanding impacts of structural difference of aliphatic and aromatic hydrocarbons on their coking behaviours

• DOI: 10.1016/j.jece.2021.106383
• Publication Date: 2021-09-20T05:16:37Z
• Authors: Félix Mérimé Bkan...; Zhiran Gao; Xianglin Xianglin; Yiran Wang; Yifan Sun; Shu Zhang; Xun Hu
• Keywords: Hexadecane; Hexane

Abstract Plastic wastes are potential feedstock for the production of hydrogen via gasification. Aliphatic hydrocarbons and aromatic hydrocarbons are important fractions from pyrolysis of plastic wastes, which might show the different reaction behaviors in steam reforming reactions due to their distinct molecular structures. To explore this, in this study, steam reforming of n-hexane and toluene, two model compounds representing respective aliphatic hydrocarbons and aromatic hydrocarbons, over Ni/SBA-15 catalyst were carried out. The in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) characterization of the steam reforming indicated that the dissociative absorption of n-hexane on nickel took place even at 100 °C, form abundant CHx species and consequently more CH4 in gaseous products. Nevertheless, the reaction intermediates from n-hexane could be gasified by the OH from adsorbed water rapidly. In comparison, the fragments from dissociative adsorption of toluene reacted with hydroxyl group of water, forming the stable intermediates bearing OH, C O, C O C and C C functionalities, which were the precursors of coke and resulted in more serious coking. The coke from steam reforming of toluene showed a higher thermal stability, higher resistivity to oxidation as it was more aromatic and contained more defective with big fused ring structures. In addition, the majority carbon nanotubes generated during steam reforming of toluene had an inner diameter of 3–6 nm and outer diameter of 10–20 nm. Nickel species on tip of the nanotubes were wrapped with a carbon layer, which contributed to the deactivation of the catalyst in steam reforming of toluene.