Plasma promotion of dry reforming: New perspectives on an old reaction

The aim of the research is to evaluate reactivity of nickel-containing catalysts in the plasma-promoted dry reforming of methane reaction (DRM). A range of nickel-containing catalysts will be synthesised and characterised. The reactivity of these materials will be tested in a spark discharge non-thermal plasma reactor. The effect of support morphology and nickel loading on reactivity in both the thermal and plasma-promoted DRM reaction was studied. A mesoporous alumina support was synthesised and wet-impregnated with 7 wt% or 14 wt% Ni. This process was repeated on a commercially available γ-alumina support. In reactions carried out at 700 °C and 900 °C highest reactivity was seen over a 7 wt% Ni on mesoporous alumina catalyst. The plasma-promoted reactions showed much lower conversions and yields compared to the thermal reactions. The plasma-only reaction (no catalyst present) gave a high conversion but similar yields to the catalysed reactions, with a high occurrence of side reactions. A study into the effects of nickel morphology on catalyst activity in the plasma-promoted DRM reaction was carried out. Three types of nickel nanoparticles were synthesised to have differing morphologies: dendrite, flake-like and spherical. These were supported on γ-alumina in pellet form. The highest reactivity in the DRM reaction was seen over the catalysts containing dendrite and flake-like Ni NPs, while the catalyst containing spherical Ni particles showed the lowest activity. Investigations into the effects of varying the applied voltage used in plasma generation, on different aspects of the reaction were studied, over a conventional wet-impregnated alumina catalyst and with no catalyst present. The materials were tested in the plasma-promoted DRM reaction at varied applied plasma-generating voltages. The effect this had on the discharge power, conversion and yield, specific energy input (SEI) and energy efficiency was studied. Results showed increasing the applied voltage increases discharge power. This effect was greater over the nickel-containing catalysts, likely related to the conductivity of the catalyst. This means that lower voltages used for plasma generation are more beneficial with regards to energy efficiency. The effects of a titania support on catalyst reactivity in the plasma-promoted DRM reaction were investigated. This was with the hopes of adding a photocatalytic effect initiated by light emitted by the plasma to the reactivity. Here, nickel particles were deposited onto both a synthesised titania support and onto Degussa P25. Wet-impregnated catalysts were also prepared on both supports. Nickel particles supported on P25 (anatase) all showed similar reactivity irrespective of nickel particle size. Those supported on a synthesised titania material showed greater variation in reactivity, following a trend of increased conversion with increased nickel particle size. The chemical looping dry reforming reaction employing a Ni-Fe based oxygen storage material as a catalyst was also studied. These materials were tested in both the thermal and plasma-promoted chemical looping DRM. Results from the thermal reactions showed CO and H2 as the main products. The plasma-catalysed reactions produced acetylene in similar levels to CO and H2. At 800 °C all catalysts deactivated following excessive carbon deposition. Plasma-promoted catalysed reactions required no activation time and showed no catalyst deactivation. Plasma-only reactions showed the highest production of acetylene, suggesting the occurrence of side reactions is mitigated when a catalyst is present.