Electrocatalytic Methane Functionalization with d⁰ Early Transition Metals Under Ambient Conditions

Abstract

The undesirable loss of methane (CH4) at remote locations welcomes approaches that ambiently functionalize CH4 on-site without intense infrastructure investment. Recently, we found that electrochemical oxidation of vanadium(V)-oxo with bisulfate ligand leads to CH4 activation at ambient conditions. The key question is whether such an observation is a one-off coincidence or a general strategy for electrocatalyst design. Here, a general scheme of electrocatalytic CH4 activation with d 0 early transition metals is established. The pre-catalysts' molecular structure, electrocatalytic kinetics, and mechanism were detailed for titanium (IV), vanadium (V), and chromium (VI) species as model systems. After a turnover-limiting one-electron electrochemical oxidation, the yielded ligand-centered cation radicals activate CH4 with low activation energy and high selectivity. The reactivities are universal among early transition metals from Period 4 to 6, and the reactivities trend for different early transition metals correlate with their d orbital energies across periodic table. Our results offer new chemical insights towards developing advanced ambient electrocatalysts of natural gas.

Recent advances in ambient electrochemical methane conversion to oxygenates using metal oxide electrocatalysts

“…22 Additionally, the electric field at the interface, the limited solubility of methane in solution, the complex adsorption-desorption kinetic process, and the high overpotential all impact the activation efficiency of methane. [51][52][53][54] Therefore, the products of methane oxidation are incredibly complex. Researchers have different opinions regarding the oxidation pathway of methane, mainly differing in their approach to how the first C-H bond of methane is disrupted.…”

Reactivity of metal dioxo complexes

“…While not explicitly a monometallic dioxo complex, another notable example of C-H activation by V-O bonds has been reported by Liu and coworkers. [10][11][12] In these reports, the vanadium oxo source is a precatalyst. The active form of the catalyst is believed to be a vanadium oxo bridged dimer bearing terminal sulfate groups.…”