From Methane to Methanol: Pd-iC-CeO2 Catalysts Engineered for High Selectivity via Mechano-Chemical Synthesis

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.

在追求将甲烷在液相中直接选择性转化为甲醇的过程中，一个常见的挑战是同时生成不希望的液体醇类或燃烧副产物。然而，本研究通过简单的机械化学合成方法制备的碳改性的单金属钯/氧化铈（Pd-CeO2）催化剂，在75°C下以过氧化氢作为氧化剂时，展现出对甲醇的100%选择性。无溶剂合成产生了独特的钯-碳-氧化铈（iC-CeO2）界面，界面碳（iC）调节了金属氧化物之间的相互作用，并促进了串联的甲烷活化和过氧化物分解，从而在75°C下实现了117 µmol/gcat的速率和100%的甲醇选择性。值得注意的是，通过DFT模拟的Eley-Rideal-like机制研究发现，H2O2（aq）的溶剂相互作用对于甲醇选择性至关重要。该机制独特地通过固态-液态-气态过程实现了甲烷直接转化为甲醇。