An Wei, Pei Yong, Zeng X C
Department of Chemistry and Nebraska Center for Materials and Nanoscience, University of Nebraska-Lincoln, Lincoln, Nebraska 68588.
Nano Lett. 2008 Jan;8(1):195-202. doi: 10.1021/nl072409t. Epub 2007 Dec 21.
We study the catalytic capability of unsupported single-walled helical gold nanotubes Au(5,3) by using density functional theory. We use the CO oxidation as a benchmark probe to gain insights into high catalytic activity of the gold nanotubes. The CO oxidation, catalyzed by the Au(5,3) nanotube, proceeds via a two-step mechanism, CO + O2 --> CO2 +O and CO + O --> CO2. The CO oxidation is initiated by the CO + O2 --> OOCO --> CO2 + O reaction with an activation barrier of 0.29 eV. On the reaction path, a peroxo-type O-O-CO intermediate forms. Thereafter, the CO + O --> CO2 reaction proceeds along the reaction pathway with a very low barrier (0.03 eV). Note that the second reaction cannot be the starting point for the CO oxidation due to the energetically disfavored adsorption of free O2 on the gold nanotube. The high catalytic activity of the Au(5,3) nanotube can be attributed to the electronic resonance between electronic states of adsorbed intermediate species and Au atoms at the reaction site, particularly among the d states of Au atom and the antibonding 2pi* states of C-O and O1-O2, concomitant with a partial charge transfer. The presence of undercoordinated Au sites and the strain inherent in the helical gold nanotube also play important roles. Our study suggests that the CO oxidation catalyzed by the helical gold nanotubes is likely to occur at the room temperature.
我们运用密度泛函理论研究了无负载的单壁螺旋金纳米管Au(5,3)的催化能力。我们以CO氧化作为基准探针，以深入了解金纳米管的高催化活性。由Au(5,3)纳米管催化的CO氧化通过两步机制进行，即CO + O2 → CO2 + O和CO + O → CO2。CO氧化由CO + O2 → OOCO → CO2 + O反应引发，其活化能垒为0.29电子伏特。在反应路径上，形成了过氧型O - O - CO中间体。此后，CO + O → CO2反应沿着反应路径以非常低的能垒（0.03电子伏特）进行。需要注意的是，由于自由O2在金纳米管上的吸附在能量上不利，第二个反应不能作为CO氧化的起点。Au(5,3)纳米管的高催化活性可归因于吸附的中间物种的电子态与反应位点处的Au原子之间的电子共振，特别是Au原子的d态与C - O和O1 - O2的反键2π*态之间的共振，同时伴随着部分电荷转移。低配位Au位点的存在以及螺旋金纳米管中固有的应变也起着重要作用。我们的研究表明，螺旋金纳米管催化的CO氧化很可能在室温下发生。
