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Abstract
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 hydrogen peroxide as 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 117 µmol/gcat at 75°C. Notably, solvent interactions of H2O2 (aq) were found to be critical for methanol selectivity through a DFT-simulated Eley-Rideal-like mechanism. This mechanism uniquely enables the direct conversion of methane into methanol via a solid-liquid-gas process.
Supplementary materials
Title
Supporting Information
Description
Experimental Work: Detailed Methane to Methanol product distribution, characterization of the material (diffraction, XANES, XPS, ATR-IR, TGA, STEM-EELS), dispersion calculations, schematics for high pressure gas-solid-liquid characterization cells
Theoretical Work: Expanded discussion of the mechanism of methanol formation on Pd-CeO2, hydrogen peroxide decomposition, charge density difference plots (CDDP) and density of states (PDOS) during the reaction, and additional justification of the Langmuir-Hinshelwood and Eley-Redeal Mechanisms over Pd-CeO2 and Pd-iC-CeO2.
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