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Catalysts 2019, 9(2), 185; https://doi.org/10.3390/catal9020185

Plasma Catalysis: Distinguishing between Thermal and Chemical Effects

1
Catalytic Processes and Materials Group, University of Twente, 7522 NB Enschede, The Netherlands
2
Nonequilibrium Fuel Conversion, DIFFER, 5612 AJ Eindhoven, The Netherlands
*
Author to whom correspondence should be addressed.
Received: 21 January 2019 / Revised: 7 February 2019 / Accepted: 7 February 2019 / Published: 16 February 2019
(This article belongs to the Special Issue Plasma Catalysis)
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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. View Full-Text
Keywords: nonequilibrium plasma; plasma catalysis; gas temperature; calcium carbonate decomposition nonequilibrium plasma; plasma catalysis; gas temperature; calcium carbonate decomposition
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Giammaria, G.; van Rooij, G.; Lefferts, L. Plasma Catalysis: Distinguishing between Thermal and Chemical Effects. Catalysts 2019, 9, 185.

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