Plasma Catalytic Conversion of CH4 to Alkanes, Olefins and H2 in a Packed Bed DBD Reactor

Abstract

<jats:p>Methane is activated at ambient conditions in a dielectric barrier discharge (DBD) plasma reactor packed with Pd/γ-alumina catalyst containing different loadings of Pd (0.5, 1, 5 wt%). Results indicate that the presence of Pd on γ-alumina substantially abates the formation of deposits, leads to a notable increase in the production of alkanes and olefins and additionally improves the energy efficiency compared to those obtained for the non-packed reactor and the bare γ-alumina packed reactor. A low amount of Pd (0.5 and 1 wt%) favors achieving a higher production of olefins (mainly C2H4 and C3H6) and a higher yield of H2. Increasing Pd loading to 5 wt% promotes the interaction of H2 and olefins, which consequently intensifies the successive hydrogenation of unsaturated compounds, thus incurring a higher production of alkanes (mainly C2H6 and C3H8). The substantial abatement of the deposits is ascribed to the role of Palladium in moderating the strength of the electric and shifting the reaction pathways, in the way that hydrogenation reactions of deposits’ precursors become faster than their deposition on the catalyst.</jats:p>

Plasma-Catalysis of Nonoxidative Methane Coupling: A Dynamic Investigation of Plasma and Surface Microkinetics over Ni(111)

“…However, as can be seen in Figure , the energy efficiency increases substantially at higher specific surface areas, reaching close to the theoretical maximum for a value of 21 000 m 2 ·g –1 . These results agree well with the work of Kasinathan et al, whose energy efficiency was estimated to be 10.8%, and the work of Taheraslani and Gardeniers, who reported energy efficiencies from 8 to 11% in the presence of a γ-alumina-supported Pd catalyst.…”

“…The energy efficiency for the plasma-only case is approximately 3% ( Figure 8 ), consistent with various works having reported values below 10%. 18 , 41 , 43 , 70 As mentioned, this poor energy efficiency is mainly due to the high proportion of energy consumed in the vibrational excitation of methane being lost through relaxation processes. 44 , 71 …”

“…Plasma-catalysis is a promising alternative for the direct upgrading of methane into higher-value products as it allows the conversion of methane at much lower temperatures than traditional thermal-catalytic routes. , The plasma-activated upgrading of methane in the presence or absence of oxidants has been the subject of numerous experimental investigations in the last two decades. A variety of catalysts and plasma discharges have been studied, − confirming the feasibility of the process. Nonetheless, a commonly reported issue is the lack of understanding of mechanistic details leading to observed performances.…”

“…The energy efficiency for the plasma-only case is approximately 3% (Figure 8), consistent with various works having reported values below 10%. 18,41,43,70 As mentioned, this poor energy efficiency is mainly due to the high proportion of energy consumed in the vibrational excitation of methane being lost through relaxation processes. 44,71 The base plasma-catalysis case (a cat = 1050 m 2 •g −1 ) has an even lower efficiency compared to the plasma-only case at about 2% on account of two effects.…”

On design of plasma jet reactor for non-oxidative methane conversion

“…In particular, acetylene and ethylene are potentially reactive, as they may participate in the formation of carbon deposition. 39 The soot can be formed by radicals obtained via hydrogen atom removal that can polymerize, triggering the formation of larger hydrocarbons and carbon deposition. 40 …”