Synergy between dielectric barrier discharge plasma and calcium oxide for reverse water gas shift

Guido Giammaria, Leon Lefferts*

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

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Abstract

This study reports on synergy between Dielectric Barrier Discharge plasma and calcium oxide as a catalyst for the Reverse Water Gas Shift (RWGS). Any effect of the presence of the catalyst on the contribution of plasma chemistry, i.e. chemical conversion in the plasma, is minimized by using a fixed bed of α-Al2O3 particles as a blank experiment and adding a small amount of calcium oxide, with similar dielectric constant, particle size and shape. This approach results in constant plasma power and ensures also that the residence time and specific energy input remain unchanged. Furthermore, synergy is determined based on reaction rates at fixed conditions, i.e. concentrations and temperature, based on kinetic equations derived from integral experiments, describing both thermal operation and plasma operation and both in absence and presence of calcium oxide. This approach has not been applied so far to study plasma-catalysis synergy.

The experimental results in thermal and plasma operation are well described with kinetic equations based on power rate laws. Synergy is observed at the lower operational temperatures (640°C) with a rate-enhancement factor of 1.7, steadily decreasing with increasing temperature until disappearing at 750°C. The concentrations of CO2, H2 and H2O have no significant influence. Synergy is attributed to a new reaction pathway involving interaction of plasma activated intermediates with the CaO surface, with a relatively low apparent activation barrier of 40 kJ mol-1. Much higher activation barriers are observed for both thermal-catalytic RWGS on CaO (140 kJ mol-1) as well as for plasma operation with Al2O3 only (90 kJ mol-1). We suggest that reaction of surface CaCO3 with plasma generated H radicals is the rate determining step, in contrast to plasma chemistry where CO2 cannot be activated with H radicals.
Original languageEnglish
Article number123806
JournalChemical Engineering Journal
Volume392
Early online date13 Dec 2019
DOIs
Publication statusPublished - 15 Jul 2020

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