title: Taming microwave plasma to beat thermodynamics in CO2 dissociation.
abstract: The strong non-equilibrium conditions provided by the plasma phase offer the opportunity to beat traditional thermal process energy efficiencies via preferential excitation of molecular vibrations. Simple molecular physics considerations are presented to explain potential dissociation pathways in plasma and their effect on energy efficiency. A common microwave reactor approach is evaluated experimentally with Rayleigh scattering and Fourier transform infrared spectroscopy to assess gas temperatures (exceeding 10(4) K) and conversion degrees (up to 30%), respectively. The results are interpreted on a basis of estimates of the plasma dynamics obtained with electron energy distribution functions calculated with a Boltzmann solver. It indicates that the intrinsic electron energies are higher than is favorable for preferential vibrational excitation due to dissociative excitation, which causes thermodynamic equilibrium chemistry to dominate. The highest observed energy efficiencies of 45% indicate that non-equilibrium dynamics had been at play. A novel approach involving additives of low ionization potential to tailor the electron energies to the vibrational excitation regime is proposed.
authors.affiliation: Dutch Institute for Fundamental Energy Research, P.O. box 6336, 5600 HH Eindhoven, The Netherlands. g.j.vanrooij@differ.nl.
authors.forename: G J
authors.initials: GJ
authors.lastname: van Rooij
authors.affiliation: Dutch Institute for Fundamental Energy Research, P.O. box 6336, 5600 HH Eindhoven, The Netherlands. g.j.vanrooij@differ.nl.
authors.forename: D C M
authors.initials: DC
authors.lastname: van den Bekerom
authors.affiliation: Dutch Institute for Fundamental Energy Research, P.O. box 6336, 5600 HH Eindhoven, The Netherlands. g.j.vanrooij@differ.nl.
authors.forename: N
authors.initials: N
authors.lastname: den Harder
authors.affiliation: Dutch Institute for Fundamental Energy Research, P.O. box 6336, 5600 HH Eindhoven, The Netherlands. g.j.vanrooij@differ.nl.
authors.forename: T
authors.initials: T
authors.lastname: Minea
authors.affiliation: Radboud University, Institute for Molecules and Materials, FELIX Laboratory, Toernooiveld 7c, 6525 ED Nijmegen, The Netherlands.
authors.forename: G
authors.initials: G
authors.lastname: Berden
authors.affiliation: Dutch Institute for Fundamental Energy Research, P.O. box 6336, 5600 HH Eindhoven, The Netherlands. g.j.vanrooij@differ.nl.
authors.forename: W A
authors.initials: WA
authors.lastname: Bongers
authors.affiliation: Department of Applied Physics, Plasma and Materials Processing Group, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands.
authors.forename: R
authors.initials: R
authors.lastname: Engeln
authors.affiliation: Dutch Institute for Fundamental Energy Research, P.O. box 6336, 5600 HH Eindhoven, The Netherlands. g.j.vanrooij@differ.nl.
authors.forename: M F
authors.initials: MF
authors.lastname: Graswinckel
authors.affiliation: Dutch Institute for Fundamental Energy Research, P.O. box 6336, 5600 HH Eindhoven, The Netherlands. g.j.vanrooij@differ.nl.
authors.forename: E
authors.initials: E
authors.lastname: Zoethout
authors.affiliation: Dutch Institute for Fundamental Energy Research, P.O. box 6336, 5600 HH Eindhoven, The Netherlands. g.j.vanrooij@differ.nl and Department of Applied Physics, Plasma and Materials Processing Group, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands.
authors.forename: M C M
authors.initials: MC
authors.lastname: van de Sanden