Altering Conversion and Product Selectivity of Dry Reforming of Methane in a Dielectric Barrier Discharge by Changing the Dielectric Packing Material

Abstract

We studied the influence of dense, spherical packing materials, with different chemical compositions, on the dry reforming of methane (DRM) in a dielectric barrier discharge (DBD) reactor. Although not catalytically activated, a vast effect on the conversion and product selectivity could already be observed, an influence which is often neglected when catalytically activated plasma packing materials are being studied. The α-Al2O3 packing material of 2.0–2.24 mm size yields the highest total conversion (28%), as well as CO2 (23%) and CH4 (33%) conversion and a high product fraction towards CO (~70%) and ethane (~14%), together with an enhanced CO/H2 ratio of 9 in a 4.5 mm gap DBD at 60 W and 23 kHz. γ-Al2O3 is only slightly less active in total conversion (22%) but is even more selective in products formed than α-Al2O3. BaTiO3 produces substantially more oxygenated products than the other packing materials but is the least selective in product fractions and has a clear negative impact on CO2 conversion upon addition of CH4. Interestingly, when comparing to pure CO2 splitting and when evaluating differences in products formed, significantly different trends are obtained for the packing materials, indicating a complex impact of the presence of CH4 and the specific nature of the packing materials on the DRM process.

Plasma-Catalytic Ammonia Synthesis beyond the Equilibrium Limit

“…This "beyond equilibrium" phenomenon has been observed in plasma-enhanced catalysis of the endothermic dry reforming of CH 4 with CO 2 . In this case, product yields are observed to exceed equilibrium yields at low bulk gas temperatures in the presence of plasma with or without catalysts [23,[32][33][34][35][36][37][38][39][40][41][42][43][44][45]. The contributions of the catalyst and plasma to observed product yields in the apparent equilibrium-limited regime are unclear.…”

“…Product yields are typically observed to increase with increasing plasma power [33,36,[38][39][40][41][42][43]46], but are insensitive to [32,36] or even decrease with increasing bulk gas temperatures [37]. Similarly, the introduction of catalyst packing into the reactor is reported sometimes to enhance [38,40,43,[46][47][48] and sometimes to diminish overall yields [33,36,38,39,44,45,47,49] relative to plasma alone. Additionally, apparent beyond-equilibrium effects on product yields for endothermic reactions like dry reforming are difficult to disentangle from local heating (hot spots) of the catalyst surface or reactor walls by the plasma [21,50].…”

The Potential Use of Core-Shell Structured Spheres in a Packed-Bed DBD Plasma Reactor for CO2 Conversion

“…Evidently, each material behaves differently based on their size, and this may be attributed to a number of material specific properties-such as dielectric constant, surface roughness, surface chemistry, electrical conductivity, heat capacity, etc., as well as the number of contact points, void space between the spheres, etc., which proved to be difficult to correlate by previous researchers [6,11]. By comparing these benchmark results with the performance of the core-shell samples in the next section, we hope to obtain some clues on the effect of the material properties with respect to their bulk or surface effect.…”

Non-Thermal Plasma for Process and Energy Intensification in Dry Reforming of Methane

“…As mentioned above the dielectric constant of the catalyst also affects the properties of the plasma. Application of a ferroelectric such as BaTiO 3 with the highest dielectric constant (Table 3) results in an increase in the plasma electric field [98].…”