Gupta Poorvi, Rana Bharti, Maurya Rishabh, Kalita Rahul, Chauhan Manav, Manna Kuntal
Department of Chemistry, Indian Institute of Technology Hauz Khas Delhi New Delhi 110016 India
Chem Sci. 2025 Jan 6;16(6):2785-2795. doi: 10.1039/d4sc06281g. eCollection 2025 Feb 5.
The direct transformation of methane into C oxygenates such as acetic acid selectively using molecular oxygen (O) is a significant challenge due to the chemical inertness of methane, the difficulty of methane C-H bond activation/C-C bond coupling and the thermodynamically favored over-oxidation. In this study, we have successfully developed a porous aluminium metal-organic framework (MOF)-supported single-site mono-copper(ii) hydroxyl catalyst [MIL-53(Al)-Cu(OH)], which is efficient in directly oxidizing methane to acetic acid in water at 175 °C with a remarkable selectivity using only O. This heterogeneous catalyst achieved an exceptional acetic acid productivity of 11 796 mmol mol h in 9.3% methane conversion with 95% selectivity in the liquid phase and can be reused at least 6 times. Our experiments, along with computational studies and spectroscopic analyses, suggest a catalytic cycle involving the formation of a methyl radical (˙CH). The confinement of Cu-active sites within the porous MIL-53(Al) MOF facilitates C-C bond coupling, resulting in the efficient formation of acetic acid with excellent selectivity due to the internal mass transfer limitations. This work advances the development of efficient and chemoselective earth-abundant metal catalysts using MOFs for the direct transformation of methane into value-added products under mild and eco-friendly conditions.
利用分子氧（O₂）将甲烷选择性地直接转化为含碳含氧化合物（如乙酸）是一项重大挑战，这是由于甲烷的化学惰性、甲烷C-H键活化/C-C键偶联的困难以及热力学上倾向的过度氧化。在本研究中，我们成功开发了一种多孔铝金属有机框架（MOF）负载的单中心单核铜（II）羟基催化剂[MIL-53(Al)-Cu(OH)]，该催化剂在175℃的水中仅使用O₂就能高效地将甲烷直接氧化为乙酸，且具有显著的选择性。这种多相催化剂在甲烷转化率为9.3%时，在液相中实现了11796 mmol mol⁻¹ h⁻¹的优异乙酸产率，选择性为95%，并且可以重复使用至少6次。我们的实验以及计算研究和光谱分析表明，催化循环涉及甲基自由基（˙CH₃）的形成。多孔MIL-53(Al) MOF中Cu活性位点的限域作用促进了C-C键偶联，由于内部传质限制，从而以优异的选择性高效形成乙酸。这项工作推动了在温和且环保的条件下，利用MOF开发高效且具有化学选择性的、地球上储量丰富的金属催化剂，用于将甲烷直接转化为增值产品。
