Plasma Catalysis: Distinguishing between Thermal and Chemical Effects

Abstract

The goal of this study is to develop a method to distinguish between plasma chemistry and thermal effects in a Dielectric Barrier Discharge nonequilibrium plasma containing a packed bed of porous particles. Decomposition of CaCO3 in Ar plasma is used as a model reaction and CaCO3 samples were prepared with different external surface area, via the particle size, as well as with different internal surface area, via pore morphology. Also, the effect of the CO2 in gas phase on the formation of products during plasma enhanced decomposition is measured. The internal surface area is not exposed to plasma and relates to thermal effect only, whereas both plasma and thermal effects occur at the external surface area. Decomposition rates were in our case found to be influenced by internal surface changes only and thermal decomposition is concluded to dominate. This is further supported by the slow response in the CO2 concentration at a timescale of typically 1 minute upon changes in discharge power. The thermal effect is estimated based on the kinetics of the CaCO3 decomposition, resulting in a temperature increase within 80 °C for plasma power from 0 to 6 W. In contrast, CO2 dissociation to CO and O2 is controlled by plasma chemistry as this reaction is thermodynamically impossible without plasma, in agreement with fast response within a few seconds of the CO concentration when changing plasma power. CO forms exclusively via consecutive dissociation of CO2 in the gas phase and not directly from CaCO3. In ongoing work, this methodology is used to distinguish between thermal effects and plasma–chemical effects in more reactive plasma, containing, e.g., H2.

Catalyst-assisted DBD plasma for coupling of methane: Minimizing carbon-deposits by structured reactors

“…In that respect, the morphology and shape of the particles have a remarkable influence on the plasma, as the electrical field is enhanced at sharp features and contact points between particles [35][36][37][38]. The catalyst and the plasma influence each other mutually in even more complex ways, including formation of microdischarges, changes in the discharge type, changes in the catalyst surface area, hot spot formation and changes in the catalytic surface properties [31,32,36,[39][40][41]. Also, activated species in the plasma, including radicals and ions, electronic excited species and vibrational excited species, may chemisorb and react on the catalyst surface.…”

CO2 Hydrogenation at Atmospheric Pressure and Low Temperature Using Plasma-Enhanced Catalysis over Supported Cobalt Oxide Catalysts

“…Despite the growing research activity in plasma-enhanced catalysis, we still do not fully understand the relationship between the catalyst properties and overall reaction performance. − This is because of the variety of the reactions and plasma configurations, which lead to different plasma species and different plasma–catalyst interactions. − Here, we study the effect of basic catalysts (MgO and Co x O y /MgO catalysts) on conversion and product selectivity during CO 2 hydrogenation. We ran the reaction in a water-cooled DBD plasma-catalysis setup, at 35 °C and ambient pressure.…”

Process intensification technologies for CO2 capture and conversion – a review

“…Compared to thermal plasma where operating temperatures can reach over 1000 K [147], non-thermal plasma is significantly more energy efficient and therefore more cost-effective as an energy source. Using non-thermal plasma to activate catalysts can facilitate thermodynamically uphill reactions [148] leading to an increased yield and selectivity at ambient temperature and atmospheric pressure avoiding catalyst sintering [149]. The synergetic effect of plasma and catalysts is shown in Fig.…”