AgII -Mediated Electrocatalytic Ambient CH4 Functionalization Inspired by HSAB Theory.

Although most class (b) transition metals have been studied in regard to CH4 activation, divalent silver (AgII ), possibly owing to its reactive nature, is the only class (b) high-valent transition metal center that is not yet reported to exhibit reactivities towards CH4 activation. We now report that electrochemically generated AgII metalloradical readily functionalizes CH4 into methyl bisulfate (CH3 OSO3 H) at ambient conditions in 98 % H2 SO4 . Mechanistic investigation experimentally unveils a low activation energy of 13.1 kcal mol-1 , a high pseudo-first-order rate constant of CH4 activation up to 2.8×103  h-1 at room temperature and a CH4 pressure of 85 psi, and two competing reaction pathways preferable towards CH4 activation over solvent oxidation. Reaction kinetic data suggest a Faradaic efficiency exceeding 99 % beyond 180 psi CH4 at room temperature for potential chemical production from widely distributed natural gas resources with minimal infrastructure reliance.

Ambient methane functionalization initiated by electrochemical oxidation of a vanadium (V)-oxo dimer.

The abundant yet widely distributed methane resources require efficient conversion of methane into liquid chemicals, whereas an ambient selective process with minimal infrastructure support remains to be demonstrated. Here we report selective electrochemical oxidation of CH4 to methyl bisulfate (CH3OSO3H) at ambient pressure and room temperature with a molecular catalyst of vanadium (V)-oxo dimer. This water-tolerant, earth-abundant catalyst possesses a low activation energy (10.8 kcal mol‒1) and a high turnover frequency (483 and 1336 hr-1 at 1-bar and 3-bar pure CH4, respectively). The catalytic system electrochemically converts natural gas mixture into liquid products under ambient conditions over 240 h with a Faradaic efficiency of 90% and turnover numbers exceeding 100,000. This tentatively proposed mechanism is applicable to other d0 early transition metal species and represents a new scalable approach that helps mitigate the flaring or direct emission of natural gas at remote locations.