Direct functionalization of methane remains a key challenge, especially for using non-noble metal catalysts. We demonstrated that TiO₂ nanorods with abundant oxygen vacancies enabled mild oxidation of methane by H₂O₂ into formaldehyde (HCHO) without light irradiation. The activity of TiO₂ nanorods with the concentration gradient of oxygen vacancies (V_O) increased with the V_O concentration. In H₂O₂ aqueous solution under 30 bar of CH₄ at 70 °C for 1 h, the TiO₂ nanorods with the most abundant V_O exhibited a total oxygenate yield of 40.80 μmol, among which the selectivity for HCHO was 64.1%. On the basis of the catalytic and spectroscopic data, we identified the reaction intermediates and accordingly mapped the reaction scheme. Specifically, H₂O₂ is activated on Ti atoms near V_O to form surface peroxo intermediates, followed by the activation of CH₄ to produce methoxy groups. The methoxy group can react either with water to form methanol or with hydroxyl radicals to form CH₃OOH. Methanol is attacked by hydroxyl radicals and dehydrated to form •CH₂OH that further reacts with hydroxyl radicals and is dehydrated to HCHO. CH₃OOH directly undergoes dehydration to engender HCHO.

中文翻译：

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富氧空位的二氧化钛作为一种高效的非贵金属催化剂，以过氧化氢为氧化剂对甲烷进行温和氧化

甲烷的直接功能化仍然是一个关键挑战，特别是对于使用非贵金属催化剂。我们证明了具有丰富氧空位的 TiO ₂纳米棒能够在没有光照射的情况下通过 H ₂ O ₂将甲烷温和氧化成甲醛 (HCHO)。具有氧空位( V _O )浓度梯度的TiO ₂纳米棒的活性随着V _O浓度的增加而增加。在 H ₂ O ₂水溶液中，在 30 bar 的 CH ₄下，70 °C 下 1 h，TiO ₂纳米棒具有最丰富的V _O总含氧量为40.80 μmol，其中对HCHO的选择性为64.1%。在催化和光谱数据的基础上，我们确定了反应中间体并相应地绘制了反应方案。具体而言，H ₂ O _2在靠近V _{O 的}Ti原子上被活化以形成表面过氧中间体，随后CH ₄被活化以产生甲氧基。甲氧基可以与水反应形成甲醇或与羟基反应形成 CH ₃ OOH。甲醇受到羟基自由基的攻击并脱水形成•CH ₂ OH，后者进一步与羟基自由基反应并脱水生成HCHO。通道₃OOH直接脱水生成HCHO。