State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China.
Proc Natl Acad Sci U S A. 2013 Sep 10;110(37):14861-6. doi: 10.1073/pnas.1306784110. Epub 2013 Aug 26.
We demonstrate that reactions confined within single-walled carbon nanotube (SWCNT) channels are modulated by the metallic and semiconducting character of the hosts. In situ Raman and X-ray absorption near-edge structure spectroscopies provide complementary information about the electronic state of carbon nanotubes and the encapsulated rhenium species, which reveal electronic interactions between encapsulated species and nanotubes. More electrons are transferred from metallic tubes (m-SWCNTs) to oxidic rhenium clusters, leading to a lower valence state rhenium oxide than that in semiconducting tubes (s-SWCNTs). Reduction in 3.5% (vol/vol) H2/Ar leads to weakened host-guest electronic interaction. The high valence state Re within s-SWCNTs is more readily reduced when raising the temperature, whereas only a sluggish change is observed for Re within m-SWCNTs. Only at 400 °C does Re reach a similar electronic state (mixture of Re(0) and Re(4+)) in both types of tubes. Subsequent oxidation in 1% O2/Ar does not show changes for Re in s-SWCNTs up to 200 °C. In comparison, m-SWCNTs facilitate the oxidation of reduced rhenium (160 °C). This can be exploited for rational design of active catalysts with stable species as a desired valence state can be obtained by selecting specific-type SWCNTs and a controlled thermal treatment. These results also provide a chemical approach to modulate reversibly the electronic structure of SWCNTs without damaging the sidewalls of SWCNTs.
我们证明了在单壁碳纳米管（SWCNT）通道内发生的反应受到主体的金属和半导体性质的调制。原位拉曼和 X 射线吸收近边结构光谱学提供了有关碳纳米管和封装铼物种的电子态的互补信息，这些信息揭示了封装物种和纳米管之间的电子相互作用。更多的电子从金属管（m-SWCNTs）转移到氧化铼簇，导致氧化态铼比在半导体管（s-SWCNTs）中更低。在 3.5%（体积/体积）H2/Ar 中还原会导致主体-客体电子相互作用减弱。当温度升高时，s-SWCNTs 中的高氧化态 Re 更容易被还原，而 m-SWCNTs 中的 Re 则只观察到缓慢的变化。只有在 400°C 下，Re 才在两种类型的管中达到相似的电子态（Re(0)和 Re(4+)的混合物）。随后在 1%O2/Ar 中氧化，在 200°C 之前，s-SWCNTs 中的 Re 没有变化。相比之下，m-SWCNTs 促进了还原铼的氧化（160°C）。这可用于合理设计具有稳定物种的活性催化剂，通过选择特定类型的 SWCNT 和受控的热处理，可以获得所需的价态。这些结果还提供了一种化学方法来可逆地调节 SWCNT 的电子结构，而不会损坏 SWCNT 的侧壁。
