Modeling plasma-based CO2conversion: crucial role of the dissociation cross section

Plasma-based CO 2 conversion is worldwide gaining increasing interest.A large research effort is devoted to improving the energy efficiency.For this purpose, it is very important to understand the underlying mechanisms of the CO 2 conversion.The latter can be obtained by computer modeling, describing in detail the behavior of the various plasma species and all relevant chemical processes.However, the accuracy of the modeling results critically depends on the accuracy of the assumed input data, like cross sections.This is especially true for the cross section of electron impact dissocation, as the latter process is believed to proceed through electron impact excitation, but it is not clear from literature which excitation channels effectively lead to dissocation.Therefore, the present paper discusses the effect of different electron impact dissociation cross sections reported in literature on the calculated CO 2 conversion, for a dielectric barrier discharge (DBD) and a microwave (MW) plasma.Comparison is made to experimental data for the DBD case, to elucidate which cross section might be the most realistic.This comparison reveals that the cross sections proposed by Itikawa and by Polak and Slovetsky both seem to underestimate the CO2 conversion.The cross sections recommended by Phelps with threshold of 7 eV and 10.5 eV yield a CO2 conversion only slightly lower than the experimental data, but the sum of both cross sections overestimates the values, indicating that these cross sections represent dissociation, but most probably also include other (pure excitation) channels.Our calculations indicate that the choice of the electron impact dissociation cross section is crucial for the DBD, where this process is the dominant mechanism for CO2 conversion.In the MW plasma, it is only significant at pressures up to 100 mbar, while it is of minor importance for higher pressures, when dissociation proceeds mainly through collisions of CO2 with heavy particles. Molecules Charged speciesRadicals Excited species CO2, CO CO2 + , CO4 + , CO + ,e l e c t r o n sThe symbols "V" and "E" between brackets for CO2, CO and O2 represent the vibrationally and electronically excited levels of these species, respectively.Details about these notations can be found