Abstract
Owing to the high hydrogen content, hydrocarbons are considered as an alternative source for hydrogen energy purposes. Complete decomposition of hydrocarbons results in the formation of gaseous hydrogen and solid carbonaceous by-product. The process is complicated by the methane formation reaction when the released hydrogen interacts with the formed carbon deposits. The present study is focused on the effects of the reaction mixture composition. Variations in the inlet hydrogen and methane concentrations were found to influence the carbon product’s morphology and the hydrogen production efficiency. The catalyst containing NiO (82 wt%), CuO (13 wt%), and Al2O3 (5 wt%) was prepared via a mechanochemical activating procedure. Kinetics of the catalytic process of hydrocarbons decomposition was studied using a reactor equipped with McBain balances. The effects of the process parameters were explored in a tubular quartz reactor with chromatographic analysis of the outlet gaseous products. In the latter case, the catalyst was loaded piecemeal. The texture and morphology of the produced carbon deposits were investigated by nitrogen adsorption and electron microscopy techniques.
Highlights
Nowadays, hydrogen is a valuable chemical product demanded in a series of industrially important processes such as the production of ammonia [1], methanol [2,3], hydrazine [4], and synthetic hydrocarbons [5]
The accumulation of the carbon by-product was monitored by McBain balances
The lowest carbon yield is expectedly found for natural gas (RM-2), which predominantly contains methane (Table 1)
Summary
Hydrogen is a valuable chemical product demanded in a series of industrially important processes such as the production of ammonia [1], methanol [2,3], hydrazine [4], and synthetic hydrocarbons [5]. According to ideas about the reaction mechanism (so-called ‘carbide cycle mechanism’), the dispersed metal particles simultaneously play a few roles: decomposition of hydrocarbon molecule with hydrogen formation and unstable carbides, diffusive transfer of carbon atoms, and subsequent deposition and growth of the graphite-like phase (carbon nanofibers) [38]. The rates of hydrogen formation and the carbon product deposition, as well as maximal hydrogen yield per 1 g of the catalyst, are known to be dependent on the catalyst’s composition, the exact composition of the hydrocarbon source, and the temperature of the process. Within the temperature interval of 500–900 ◦ C, which targets the decomposition of hydrocarbons, methane formation reaction (2) always takes place This fact explains the driving force’s appearance for the carbon hydrogenation process in any hydrocarbon cases, except methane itself. The main focus is on the conceptual aspects of the catalytic process of hydrocarbons’ decomposition
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