Directly converting methane to methanol, bypassing compression and liquefaction, poses a key challenge due to methane's stable C-H bond. Integrating all reaction steps into a single reactor offers an energy-efficient approach, simplifying the complex reaction network and operating below water's boiling point. Furthermore, the use of metal oxide based materials allows for unique metal-support interactions that promote the selective formation of methanol instead of undesirable liquid and combustion products.
In the pursuit of selective conversion of methane directly to methanol in the liquid-phase, a common challenge is the concurrent formation of undesirable liquid oxygenates or combustion byproducts. However, we demonstrate that monometallic Pd-CeO₂ catalysts, modified by carbon, created by a simple mechanochemical synthesis method exhibit 100% selectivity towards methanol at 75°C, using dilute hydrogen peroxide as the oxidizing agent. The solvent free synthesis yields a distinctive Pd-iC-CeO₂ interface, where interfacial carbon (iC) modulates metal-oxide interactions and facilitates tandem methane activation and peroxide decomposition, thus resulting in an exclusive methanol selectivity of 100% with a rate of 115 µmol/gcat at 75°C. Notably, solvent interactions of H₂O₂ (aq) were found to be critical for methanol selectivity through various in situ solution phase characterization, including high pressure liquid phase in situ XAFS, high pressure in situ ¹H-NMR, liquid phase NEXAFS, and liquid phase in situ ATR-IR. Through the integration of cutting-edge experimental techniques with DFT simulations incorporating implicit solvent treatment of hydrogen peroxide molecules, we have identified a distinct interface capable of selectively producing methanol directly from natural gas.

Sara Colussi

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