Solution Catalytic Cycle of Incompatible Steps for Ambient Air Oxidation of Methane to Methanol

Abstract

Direct chemical synthesis from methane and air under ambient conditions is attractive yet challenging. Low-valent organometallic compounds are known to activate methane, but their electron-rich nature seems incompatible with O2 and prevents catalytic air oxidation. We report selective oxidation of methane to methanol with an O2-sensitive metalloradical as the catalyst and air as the oxidant at room temperature and ambient pressure. The incompatibility between C–H activation and O2 oxidation is reconciled by electrochemistry and nanomaterials, with which a concentration gradient of O2 within the nanowire array spatially segregated incompatible steps in the catalytic cycle. An unexpected 220 000-fold increase of the apparent reaction rate constants within the nanowire array leads to a turnover number up to 52 000 within 24 h. The synergy between nanomaterials and organometallic chemistry warrants a new catalytic route for CH4 functionalization.

Efficacy analysis of compartmentalization for ambient CH4 activation mediated by a RhII metalloradical in a nanowire array electrode

“…Generally applicable for non-enzymatic cascade design as noted above, one question that we ask is whether our previously reported design employing the nanowire array and a concentration gradient is effective in utilizing the ephemeral O 2 -sensitive intermediate, Rh II , whose activation of CH 4 was considered turnover-limiting. 20,24 Our approach to this question is to construct a numerical model in the context of compartmentalization and analyze the reaction efficiency g that will be valuable for future design consideration. Fig.…”

“…12,22 The overall process was reported to be catalytic, achieving a turnover number up to 52 000 within 24 hours. 20 The synergy between nanomaterials and organometallic chemistry warrants a new catalytic route of CH 4 functionalization, while additional studies are needed to understand the underlying mechanism and quantitatively evaluate the efficacy of the strategy that interfaces nanowires with organometallics. 23 Here we report our analysis of the above-mentioned CH 4 -to-CH 3 OH catalysis in the context of a compartmentalized cascade.…”

Electricity-powered artificial root nodule

“…Moreover, in air, the electrochemical Planar p = 60 μm p = 30 μm p = 15 μm p = 10 μm z (μm) reduction of O 2 on electrode's surface consumes O 2 and creates a local O 2 gradient in the solution. This effect is much more pronounced for porous and large-surface-area electrodes in general [24][25][26][27] , effectively creating an O 2 -free domain within the wire array suitable for anaerobic N 2 fixation ( Fig. 1b).…”

“…1b). Our previous work demonstrated a O 2 -free domain within a nanowire array electrode 23,25 , which allows anaerobic microbial reduction of CO 2 in air 23 . Here we apply the same design principle for an artificial root nodule.…”

Control of Substrates Beyond the Catalyst Active Site

“…This chemistry of nanomaterials is where Liu and co-workers make a contribution with this report. 1 Liu and co-workers employ the known chemistry of (tetramesitylporphyrin)Rh II , (TMP)Rh II , in its reaction with half an equivalent of methane (CH 4 ) to give (TMP)Rh III –H and (TMP)Rh III –CH 3 . 9,10 Protection of these highly air-sensitive reagents and products is achieved by positioning of (TMP)Rh II inside a nanowire array.…”