Direct cyanomethylation of aliphatic and aromatic hydrocarbons with acetonitrile over a metal loaded titanium oxide photocatalyst
Direct cyanomethylation of aliphatic and aromatic hydrocarbons with acetonitrile over a metal loaded titanium oxide photocatalyst
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DOI：
10.1039/c7cy00365j
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发表时间：
2017-06
影响因子：
5
通讯作者：
E. Wada;T. Takeuchi;Yukihiro Fujimura;A. Tyagi;Tatsuhisa Kato;H. Yoshida
中科院分区：
文献类型：
--
作者：
E. Wada;T. Takeuchi;Yukihiro Fujimura;A. Tyagi;Tatsuhisa Kato;H. Yoshida
负载铂的TiO 2（Pt/TiO 2）光催化剂促进脂族烃（即环己烷和环己烯）与乙腈的氰甲基化，其中光生空穴氧化解离乙腈和脂族烃两者的C-H键以在它们的自由基交叉偶联之前形成每个相应的自由基物种。Pt/TiO2光催化剂比Pd/TiO2光催化剂在这些反应中的活性更高。相比之下，苯的氰甲基化被Pd/TiO2光催化剂或Pt/TiO2光催化剂和由Al2O3负载的Pd催化剂的物理混合物促进，而单独的Pt/TiO2光催化剂几乎不促进。反应速率的温度依赖性证明了Pd纳米颗粒在TiO2光催化剂上的热功能作为金属催化剂。这些结果清楚地表明Pd金属催化剂对于苯的氰甲基化是必需的。然而，在脂族烃的氰甲基化中，没有观察到金属颗粒的催化作用，这意味着自由基偶联在没有金属催化的情况下发生。因此，可以得出结论，在苯氰甲基化的情况下，Pd纳米粒子发挥双重作用，作为催化剂，催化苯与氰甲基自由基的取代反应，并作为电子接收器，以减少光激发的电子和空穴在TiO 2光催化剂中的重组，虽然它们不能作为催化剂的脂肪烃的氰甲基化。
A platinum-loaded TiO2 (Pt/TiO2) photocatalyst promoted cyanomethylation of aliphatic hydrocarbons, namely cyclohexane and cyclohexene, with acetonitrile, where the photogenerated hole oxidatively dissociates the C–H bond of both the acetonitrile and the aliphatic hydrocarbons to form each corresponding radical species before their radical cross-coupling. The Pt/TiO2 photocatalyst was more active than the Pd/TiO2 photocatalyst in these reactions. In contrast, the cyanomethylation of benzene was promoted by the Pd/TiO2 photocatalyst or a physical mixture of the Pt/TiO2 photocatalyst and a Pd catalyst supported by Al2O3, while it was hardly promoted by the Pt/TiO2 photocatalyst alone. The temperature dependence of the reaction rate proved that the Pd nanoparticles on the TiO2 photocatalyst thermally function as a metal catalyst. These results clearly suggest that the Pd metal catalyst is necessary for the cyanomethylation of benzene. However, in the cyanomethylation of aliphatic hydrocarbons, the catalytic effect of the metal particles was not observed, meaning that the radical coupling takes place without the metal catalysis. Thus, it is concluded that in the case of the benzene cyanomethylation the Pd nanoparticles play dual roles, as a catalyst to catalyse the substitution reaction of benzene with the cyanomethyl radical, and as an electron receiver to reduce the recombination of the photoexcited electrons and holes in the TiO2 photocatalyst, although they could not contribute as a catalyst to the cyanomethylation of aliphatic hydrocarbons.