The direct conversion of methane to methanol would provide a route to circumvent flaring at oil refineries and extraction sites while also valorizing natural gas, a cleaner carbon fuel than common petroleum. This could ease carbon emissions in the interim as carbon neutral technologies develop. Copper containing zeolites can perform this reaction under relatively mild conditions, an impressive feat given methane’s large 105 kcal/mol C-H bond and the thermodynamic tendency to overoxidize methane to CO2. Although these materials show great promise, they are difficult to study and thus optimize given the large amount of spectator metal sites that obscure the active site signal. Our group has implemented site-selective spectroscopies, in particular resonance Raman (rR), to identify a highly reactive mono-(μ-oxo) dicopper(II) [Cu2O]2+ species found in multiple zeolite topologies. Using rR, Magnetic Circular Dichroism, Electron Paramagnetic Resonance, and X-Ray Absorption Spectroscopy, we have rigorously defined a second copper active site motif that selectively converts CH4 to CH3OH, the first well defined mononuclear copper active site. This definitively shows that a mononuclear cupric site can perform this critical chemistry. We also use kinetic studies to compare the reactivity between the mononuclear and binuclear sites and couple density functional theory to our experimental observations to elucidate how metal nuclearity results in a substantial reactivity differential between the two sites.

Methane activation by a mononuclear cu(II) zeolite active site: Comparison to binuclear cu(II) reactivity

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ACS Fall 2022

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