Methane, an abundant resource in the U.S., has very strong C-H bonds, which makes it energy consuming to be activated. Thus, the development of catalysts to upgrade methane to higher value products is challenging but very desirable. Two major issues that current methane upgrading processes are facing are that high temperatures (up to 900 K) are required,1 and the short life time of the catalysts caused by sintering and coking.2 We aim to address these issues and pursue a low temperature process, which leverages the use of an electrochemical cell to convert methane to methanol. The process uses carbonate anions (CO32-) that are produced at the cathode and transferred to the anode. At the anode, carbonate anions deliver a single oxygen atom that can selectively oxidize methane to methanol. The fact that CO32- reduction leads again to CO2, which desorbs into the gas phase, is considered a key advantage of the proposed electrochemical process. The rate of CO32- delivery can be controlled by adjusting the cell potential and current density. By simultaneously controlling the flow rate of CH4 at the anode, we anticipate that the prevention of methane over-oxidation, such that a high yield of methanol can be achieved. To obtain fundamental insights into the process, we have performed density functional theory (DFT) calculations on Ni(111) and NiO(100) and explicitly accounted for the effects of applied electric fields. Our results indicate that the interaction between the electric field and the surface dipole moment plays the dominant role in altering the binding behavior. Hence, the reaction enthalpies and activation barriers of certain elementary steps exhibit a strong dependence on the electric field. We have quantified the electric field effect for two distinct reaction pathways and the results show that a positive electric field lowers the activation barriers of most steps. Although the decrease of the activation barriers is small, we postulate that a properly tuned electric field can guide the reaction to proceed in the desired direction. While the development of a viable process remains in its early stages, our results suggest that an electrochemical cell using CO32- as an oxidant offers unique advantages for selectively upgrading methane to value-added products.

Carbonate-assisted electrochemical methane conversion to methanol on Ni(111) and NiO(100): Density functional theory study

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.