Photocatalytic transformation of methane to ethane and hydrogen (2CH₄ → C₂H₆ + H₂) is enhanced over metallic cocatalyst-loaded Ga₂O₃ particles under gas-flow conditions with water vapor. We examined the photocatalytic activity of oxide materials (Ga₂O₃, NaTaO₃:La, SrTiO₃:Al, and AgTaO₃) loaded with Pd or Rh–Cr oxides, which are hydrogen-evolving cocatalysts. Electron spin resonance analysis revealed that the hydroxyl radical (^•OH) generated through the single-electron oxidation of water is the active species for methane activation to produce C₂H₆ and carbon dioxide over Pd/Ga₂O₃ and Pd/NaTaO₃:La photocatalysts. In contrast, the photocatalysts active for water vapor splitting rather than methane transformation generate a surface peroxyl radical (superoxo) moiety as an intermediate of oxygen evolution. For methane activation, the ionization potentials (valence band maximum and midgap surface states) of the photocatalysts should be sufficiently high to promote single-electron transfer from the water to generate ^•OH since methane exhibits high oxidation potential. This study unravels the crucial role of surface energy levels of photocatalysts for the activation of methane with water vapor.

中文翻译：

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通过从水分子到半导体光催化剂表面态的单电子转移来活化甲烷

在水蒸气气流条件下，负载金属助催化剂的Ga ₂ O ₃颗粒增强了甲烷光催化转化为乙烷和氢气(2CH ₄ → C ₂ H ₆ + H ₂ )。我们研究了负载 Pd 或 Rh-Cr 氧化物（析氢助催化剂）的氧化物材料（Ga ₂ O ₃、NaTaO ₃ :La、SrTiO ₃ :Al 和 AgTaO ₃ ）的光催化活性。电子自旋共振分析表明，水单电子氧化产生的羟基自由基( ^{· OH)是甲烷在Pd/Ga} ₂ O ₃和Pd/NaTaO ₃上活化生成C ₂ H ₆和二氧化碳的活性物种。 ：La光催化剂。相比之下，光催化剂对水蒸气分解而不是甲烷转化具有活性，产生表面过氧自由基（超氧）部分作为氧析出的中间体。对于甲烷活化，光催化剂的电离势（价带最大值和中带隙表面态）应足够高，以促进单电子从水中转移以生成^· OH，因为甲烷表现出高氧化势。这项研究揭示了光催化剂表面能水平对于水蒸气活化甲烷的关键作用。