Plasma-Catalytic Partial Oxidation of Methane on Pt(111): A Microkinetic Study on the Role of Different Plasma Species

Abstract

We use microkinetic modeling to examine the potential of plasma-catalytic partial oxidation (POX) of CH 4 as a promising new approach to produce oxygenates. We study how different plasma species affect POX of CH 4 on the Pt(111) surface, and we discuss the associated kinetic and mechanistic changes. We discuss the effect of vibrationally excited CH 4 and O 2 , as well as plasma-generated radicals and stable intermediates. Our results show that vibrational excitation enhances the turnover frequency (TOF) of catalytic CH 4 dissociation and has good potential for improving the selectivities toward CH 3 OH, HCOOH, and C 2 hydrocarbons. Nevertheless, when also considering plasma-generated radicals, we find that these species mainly govern the surface chemistry. Additionally, we find that plasma-generated radicals and stable intermediates enhance the TOFs of CO x and oxygenates, increase the selectivity toward oxygenates, and make the formation of HCOOH more significant on Pt(111). We also briefly illustrate the potential impact of Eley− Rideal reactions that involve plasma-generated radicals. Finally, we reveal how various radicals affect the catalyst surface chemistry and we link this to the formation of different products. This allows us to make suggestions on how the plasma composition should be altered to improve the formation of desired products.

Selective oxidation of CH4 to CH3OH through plasma catalysis: Insights from catalyst characterization and chemical kinetics modelling

“…[22][23][24][25][26][27] Generally, the gas temperature in NTP remains near room temperature, while the generated electrons exhibit a typical temperature of 1-10 eV (~ 10 4 -10 5 K), which is sufficient to activate feed gas molecules (e.g., CH4 and O2) into reactive species, including radicals, excited atoms and molecules, and ions. Several scientists have studied SOMTM by O2 through plasma and/or plasma catalysis, [28][29][30][31][32][33][34][35][36] but only a few have reported satisfying CH3OH selectivity. Nozaki applied a microplasma and obtained a CH4 conversion to synthetic fuels with maximum organic liquid selectivity of 70 % without catalysts (plasma alone), [28] but the CH3OH selectivity was below 15 %.…”

“…[32] In addition, insights from microkinetic modelling for plasma-catalytic SOMTM process were obtained on Pt(111) surface and the results showed that vibrational excitation and especially radicals produced from CH4/O2 NTP could enhance the turnover frequency (TOF) and improve the selectivity of CH3OH, HCOOH and C2 hydrocarbons. [33] In general, this field is still in the early research stages and fundamental information on the interaction of NTP with a catalyst is still lacking, and the limited CH3OH selectivity in most studies is attributed to the further oxidation of CH3OH into CO and CO2. [34] Additionally, the reaction pathway for the production of CH3OH and by-products (HCHO, HCOOH, CO and CO2) from CH4 and O2 in NTP is largely unknown.…”

“…As mentioned above, in plasma alone, we achieved 42 % CH3OH selectivity (Figure 1A), which is much better than most results in literature. [28][29][30][31][32][33][34][35][36] To explain this result, we performed chemical kinetics modelling of CH4/O2 DBD plasma using…”

Advances in non-equilibrium $$\hbox {CO}_2$$ plasma kinetics: a theoretical and experimental review

“…Some models have been developed to describe the catalyst surface chemistry upon impact of plasma species, by means of 0D (microkinetics) plasma chemistry and/or catalyst surface chemistry models, e.g., for plasma-catalytic NH 3 synthesis [409][410][411][412], nonoxidative coupling of CH 4 [413], and very recently also for CO 2 hydrogenation [414] and CH 4 partial oxidation [415]. Such models reveal the reaction pathways at the catalyst surface and the role of plasma-generated radicals and (vibrationally or electronically) excited.…”

Energetics of pathways enabled by experimentally detected radicals during catalytic, plasma-assisted NH3 synthesis

“…On the other hand, Bogaerts and coworkers have recently assumed energy barriers for ER reactions involving radicals to be zero. 47 Thus, to examine the typical barrier for ER reactions, we chose to directly study the reaction coordinates for reactions r3 to r8 using CI-NEB calculations on at least three metals each:…”