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Synergistic effects of plasma–catalyst interactions for CH4 activation

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Abstract

The elucidation of catalyst surface–plasma interactions is a challenging endeavor and therefore requires thorough and rigorous assessment of the reaction dynamics on the catalyst in the plasma environment. The first step in quantifying and defining catalyst–plasma interactions is a detailed kinetic study that can be used to verify appropriate reaction conditions for comparison and to discover any unexpected behavior of plasma-assisted reactions that might prevent direct comparison. In this paper, we provide a kinetic evaluation of CH4 activation in a dielectric barrier discharge plasma in order to quantify plasma–catalyst interactions via kinetic parameters. The dry reforming of CH4 with CO2 was studied as a model reaction using Ni supported on γ-Al2O3 at temperatures of 790–890 K under atmospheric pressure, where the partial pressures of CH4 (or CO2) were varied over a range of ≤25.3 kPa. Reaction performance was monitored by varying gas hourly space velocity, plasma power, bulk gas temperature, and reactant concentration. After correcting for gas-phase plasma reactions, a linear relationship was observed in the log of the measured rate constant with respect to reciprocal power (1/power). Although thermal catalysis displays typical Arrhenius behavior for this reaction, plasma-assisted catalysis occurs from a complex mixture of sources and shows non-Arrhenius behavior. However, an energy barrier was obtained from the relationship between the reaction rate constant and input power to exhibit ≤∼20 kJ mol−1 (compared to ∼70 kJ mol−1 for thermal catalysis). Of additional importance, the energy barriers measured during plasma-assisted catalysis were relatively consistent with respect to variations in total flow rates, types of diluent, or bulk reaction temperature. These experimental results suggest that plasma-generated vibrationally-excited CH4 favorably interacts with Ni sites at elevated temperatures, which helps reduce the energy barrier required to activate CH4 and enhance CH4 reforming rates.

Graphical abstract: Synergistic effects of plasma–catalyst interactions for CH4 activation

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Publication details

The article was received on 01 Mar 2017, accepted on 25 Apr 2017 and first published on 28 Apr 2017


Article type: Paper
DOI: 10.1039/C7CP01322A
Citation: Phys. Chem. Chem. Phys., 2017, Advance Article
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    Synergistic effects of plasma–catalyst interactions for CH4 activation

    J. Kim, D. B. Go and J. C. Hicks, Phys. Chem. Chem. Phys., 2017, Advance Article , DOI: 10.1039/C7CP01322A

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