Development of a microkinetic model for non-oxidative coupling of methane over a Cu catalyst in a non-thermal plasma reactor

Abstract

AA surface microkinetic plasma model for non-oxidative coupling of methane into H2 and higher hydrocarbons was developed over a Cu catalytic film. Twenty key plasma species including electron, ions, radicals, and neutrals were considered in respective chemical reactions leading to the formation of C2 hydrocarbons onto the catalyst surface. The kinetic model was coupled with a global plasma model to describe the performance of a non-thermal plasma reactor. In the reactor model, the reactant gas flows between the two coaxial cylindrical metal electrodes with a length of 50 mm and a diameter of 2 mm (inner) and 6 mm (outer electrode) coated with a Cu film. The effect of discharge power, initial CH4 concentration, and inlet flow rate on methane conversion was investigated. The surface model shows that the CH4 conversion of 47% is obtained at a discharge power of 70 W with a selectivity of C2H2 (49%). Increase in power increased the conversion of methane while increase in pressure and/or inlet gas flow rate decreased it. Also, the results of the plasma-catalyst model were compared with those of plasma alone (without catalyst). It showed that presence of the catalyst inside the plasma increases the selectivity and yield of acetylene, while it deceases the selectivity and yield of hydrogen. Also, the density of radical CH3 in the plasma phase increased in the presence of the catalyst, while CH2 and CH densities decreased with that.

Is a catalyst always beneficial in plasma catalysis? Insights from the many physical and chemical interactions

“…Pourali et al [115] constructed a CSTR model to study plasma-catalytic non-oxidative coupling of CH4 over a Cu(211) catalyst. A constant plasma power was deposited into the reactor volume, rather than a pulsed power profile.…”

“…In our own model, we also apply the CSTR approach, similar to refs. [72,73,102,115], meaning that the densities of the gas species and the surface coverages are considered to be uniformly distributed over the reactor volume. However, rather than applying a constant power density as was done in refs.…”

“…59 [102,115], we calculate the rate coefficients for electron impact dissociation at the breakdown electric field and multiply these by the fraction of the reactor volume that is occupied by microdischarges, as described in section S3 of the SI. This way, we attain a volume-averaged rate coefficient for radical production that is representative for a DBD plasma.…”

“…[ 102,115]), the maximum power density would be much lower compared to when the plasma power is concentrated in the microdischarges. Consequently, much less electrons would reach the energy threshold for electron impact dissociation, and the associated rates would be clearly underestimated.…”

Nonoxidative methane coupling in a micro‐DBD with enhanced secondary electron emission

“…The use of NTP for the methane activation-based synthesis of chemicals and fuels has gained popularity recently. [15][16][17] Recently, we have shown theoretically and computationally that dielectric barrier discharges with charge injection points have further practical benefits. [18,19] Following that, in this experimental study, we explore methane conversion in an AC-driven charge injector DBD and compare the results to the usual flat electrode DBD plasma.…”