The catalytic conversion of methane to liquid fuels and chemicals remains a challenge in catalysis. Methane is a stable molecule; the chemical inertness of the C-H bond in this compound (434 kJ mol-1) requires high energy input and temperatures for activation. CH4 transformation to light olefins and aromatics involves an indirect route via synthesis gas, where products such as olefins, gasoline and diesel can be obtained from the well-established Fischer-Tropsch synthesis. However, thermal conversion of CH4 encounters many issues, mainly due to the high energy demand and catalyst instability due to carbon deposition. An alternative solution to overcome is possible through non-thermal plasma-assisted conversion of methane. A non-thermal plasma is an atmospheric pressure plasma where breakdown of a gas produces partial ionization, resulting in a non-equilibrium between the temperature of the electrons (104-105 K) and that of the heavy particles, such as ions, molecules, and radicals, remain close to the ambient temperature of the gas. Methane dehydroaromatization is a non-oxidative approach to directly convert methane into aromatics and hydrogen over a Mo/H-ZSM-5 catalyst, where 14% equilibrium conversion is achieved at 973 K. Herein, through a plasma-catalytic methane dehydroaromatization process, we show that we can drive this chemistry at lower bulk gas temperatures, where thermal methane conversion is not possible. In the plasma-only reaction, we observed the influence of bulk gas temperature on the behavior of the plasma discharge in the absence of a catalyst, leading to lower methane conversions as the temperature is increased. However, plasma-catalytic studies show that incorporation of Mo/H-ZSM-5 in the plasma discharge significantly enhances methane conversion under the same conditions, while shifting the product distribution towards aromatics. This presentation will focus on our current understanding of the complex, plasma-catalytic methane dehydroaromatization mechanism and how plasma stimulation promotes the low temperature reaction.

Facilitating methane dehydroaromatization pathways over Mo/H-ZSM-5 under non-thermal plasma stimulation

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ACS Fall 2022

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