Direct and Selective Photocatalytic Oxidation of CH4 to Oxygenates with O2 on Cocatalysts/ZnO at Room Temperature in Water
Direct and Selective Photocatalytic Oxidation of CH4 to Oxygenates with O2 on Cocatalysts/ZnO at Room Temperature in Water
复制标题
室温下在水中助催化剂/ZnO 上用 O2 直接选择性光催化将 CH4 氧化为氧气。
DOI：
10.1021/jacs.9b11440
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发表时间：
2019-12-25
影响因子：
15
通讯作者：
Ye, Jinhua
中科院分区：
文献类型：
--
作者：
Song, Hui;Meng, Xianguang;Ye, Jinhua
甲烷直接转化为甲醇和其他液态氧化合物在激活甲烷的第一个C-H键和抑制过氧化方面仍然面临相当大的挑战。在这里，我们报道了ZnO负载适当的助催化剂（Pt, Pd， Au或Ag），在室温下，仅以分子氧作为氧化剂，就可以在水中直接氧化甲烷为甲醇和甲醛。在负载0.1 wt % Au的10 mg ZnO溶液中，可获得高达250微摩尔的液体氧合物，选择性达95%。同位素标记氧和水的实验表明，氧-2分子而不是水是CH4直接氧化的氧源。我们发现ZnO和助催化剂可以共同激活水中的CH4和O-2生成甲基自由基和轻度氧化中间体（氢过氧自由基），这是CH4直接氧化生成含氧液体产物的两个关键前体中间体。我们的研究强调了实现CH4直接和选择性光氧化成液态氧的两个同样重要的方面，即CH4的高效C-H键活化和O-2的可控活化。
Direct conversion of methane into methanol and other liquid oxygenates still confronts considerable challenges in activating the first C-H bond of methane and inhibiting overoxidation. Here, we report that ZnO loaded with appropriate cocatalysts (Pt, Pd, Au, or Ag) enables direct oxidation of methane to methanol and formaldehyde in water using only molecular oxygen as the oxidant under mild light irradiation at room temperature. Up to 250 micromoles of liquid oxygenates with similar to 95% selectivity is achieved for 2 h over 10 mg of ZnO loaded with 0.1 wt % of Au. Experiments with isotopically labeled oxygen and water reveal that molecular O-2, rather than water, is the source of oxygen for direct CH4 oxidation. We find that ZnO and cocatalyst could concertedly activate CH4 and O-2 into methyl radical and mildly oxidative intermediate (hydroperoxyl radical) in water, which are two key precursor intermediates for generating oxygenated liquid products in direct CH4 oxidation. Our study underlines two equally significant aspects for realizing direct and selective photooxidation of CH4 to liquid oxygenates, i.e., efficient C-H bond activation of CH4 and controllable activation of O-2.