Unravelling the pathways of catalytic methane functionalization sets the foundations for the efficient production of valuable chemicals and fuels from this abundant feedstock. The catalytic oxybromination of methane into platform compounds bromomethane and dibromomethane constitutes a prominent example, although it displays a puzzling reaction network that has been speculated to involve free-radical intermediates. Here, photoelectron photoion coincidence spectroscopy with synchrotron radiation was used to provide evidence of the evolution of gaseous methyl and bromine radicals over (VO)₂P₂O₇ and EuOBr catalysts and the strong correlation between the formation of methyl radicals and the production of bromomethanes. Complemented by kinetic data on methane oxybromination and non-catalytic methane bromination, these results imply the surface-catalysed generation of bromine radicals and molecular bromine followed by the gas-phase methane bromination, which is rationalized by density functional theory calculations. The findings emphasize the role of both surface and gas-phase steps in halogen-mediated C–H bond activation over heterogeneous catalysts.

揭示催化甲烷功能化的途径为从这种丰富的原料有效生产有价值的化学物质和燃料奠定了基础。甲烷催化氧溴化成平台化合物溴甲烷和二溴甲烷构成了一个突出的例子，尽管它显示出令人费解的反应网络，据推测它涉及自由基中间体。在此，使用具有同步加速器辐射的光电子光子重合能谱提供了在（VO）₂ P ₂ O ₇上气态甲基和溴自由基的演变的证据。和EuOBr催化剂，以及甲基自由基的形成与溴甲烷的产生之间的强相关性。补充有关甲烷氧溴化和非催化甲烷溴化的动力学数据，这些结果表明表面催化生成溴自由基和分子溴，然后是气相甲烷溴化，这通过密度泛函理论计算得以合理化。研究结果强调了表面步骤和气相步骤在非均相催化剂上卤素介导的C–H键活化中的作用。