Direct conversion of methane to formaldehyde and CO on B₂O₃ catalysts

Direct oxidation of methane to value-added C₁ chemicals (e.g. HCHO and CO) provides a promising way to utilize natural gas sources under relatively mild conditions. Such conversions remain, however, a key selectivity challenge, resulting from the facile formation of undesired fully-oxidized CO₂. Here we show that B₂O₃-based catalysts are selective in the direct conversion of methane to HCHO and CO (~94% selectivity with a HCHO/CO ratio of ~1 at 6% conversion) and highly stable (over 100 hour time-on-stream operation) conducted in a fixed-bed reactor (550 °C, 100 kPa, space velocity 4650 mL g_cat^-1 h^-1). Combined catalyst characterization, kinetic studies, and isotopic labeling experiments unveil that molecular O₂ bonded to tri-coordinated BO₃ centers on B₂O₃ surfaces acts as a judicious oxidant for methane activation with mitigated CO₂ formation, even at high O₂/CH₄ ratios of the feed. These findings shed light on the great potential of designing innovative catalytic processes for the direct conversion of alkanes to fuels/chemicals.