Selective oxidative coupling of methane via surface-confined methyl-radical transformation

Directly converting methane into valuable-added chemicals and fuels is a grand challenge in chemistry. Methyl radical (CH3), a highly reactive and short-lived key intermediate, is generally involved in direct-methane-conversion processes, but its reaction is difficult to control, especially at elevated temperatures in the presence of oxygen. The uncontrollable homogeneous transformation of CH3 in oxidative coupling of methane (OCM) places an inherent upper bound on single-pass C2 yield (~ 28%) independent of catalyst, which is the major obstacle for its large-scale utilization. Here we report that surface-confined CH3 coupling represents a general strategy for the design of selective oxidative coupling of methane (SOCM) to perform controllable radical reactions. We show that tungstate sub-nanoclusters, embedded within ZrO2 matrix, can efficiently capture highly reactive CH3 and selectively convert them into C2 products. Experimental results and kinetic modeling unambiguously show that combining catalysts for CH3 generation versus capture can be an effective approach for improving OCM catalyst performance and breaking away from limits imposed by gas-phase kinetics. It achieves C2 yield of >30% at 650 – 700 °C and a world-record single-pass C2 yield (46.3%) far beyond the fundamental upper C2 yield bound at 800 °C. We anticipate that selective oxidative coupling of methane (SOCM) is economically competitive with current oil-based technology for ethylene production.