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首页> 外文期刊>The journal of physical chemistry, B. Condensed matter, materials, surfaces, interfaces & biophysical >Ethyne Adsorbed on CuNaY Zeolite: FTIR Spectra and Quantum Chemical Calculations
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Ethyne Adsorbed on CuNaY Zeolite: FTIR Spectra and Quantum Chemical Calculations

机译：乙炔吸附在CuNaY沸石上：FTIR光谱和量子化学计算

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The interaction of ethyne with vacuum-dehydrated CuNaY zeolite has been investigated by means of Fourier transform infrared spectroscopy and cluster model density functional theory calculations. The spectra show three bands: two which are symmetry-forbidden for the free molecule but become allowed in the adsorbed state (the v_1 CC stretching mode at ～1832 and 1814-1812 cm~(-1), and the symmetric v_2 CH stretching mode at 3271 and 3251 cm~(-1)), and the allowed antisymmetric v_3 CH stretching mode at 3202 and 3174 cm~(-1). They all appear in pairs. The two components of the bands, which are all strongly shifted to lower wavenumbers relative to the free molecule, are attributed to two inequivalent Cu~+ adsorption sites. On increasing C_2H_2 pressure, the more strongly shifted components appear first and acquire significantly higher intensity, indicating that they must correspond to the more strongly bound site. Analysis of the geometry of the complexes representing ethyne adsorbed on Cu at both sites yields a four-fold coordination of copper, including two oxygen atoms and side-on bound C_2H_2, with CC bonds elongated by 0.03 A and CCH angles reduced by at least 14.7°. The calculated binding energies of the two ethyne-copper complexes are significantly different due to the energy necessary to reach the geometry within Cu(SII)-C_2H_2 from the relaxed Cu(SII) cluster. C_2H_2 is more strongly adsorbed on Cu(SIII) (in the saddle between two four-membered rings near the wall of a supercage) than on site II (above a six-ring window of a sodalite cage). Population analysis provides a net charge transfer of about 0.14e toward the ethyne. An energy decomposition method demonstrates the paramount importance of electrostatic and charge-transfer contributions to the Cu-zeolite-ethyne interaction energy. The harmonic frequency calculation suggests that the more strongly shifted band components of all stretching vibrations have to be assigned to C_2H_2 adsorbed on Cu~+ at SIII, which is the more stable site. Apart from the overestimated Δv_1 values, the vibrational frequency shifts calculated for both adsorption complexes are in excellent agreement with the experimental ones.
机译：通过傅里叶变换红外光谱和聚类模型密度泛函理论计算，研究了乙炔与真空脱水的CuNaY沸石的相互作用。光谱显示三个带：两个带对自由分子是对称禁止的，但在吸附状态下被允许（在〜1832和1814-1812 cm〜（-1）处的v_1 CC拉伸模式，和在对称状态下的对称v_2 CH拉伸模式）在3271和3251 cm〜（-1）处，允许的反对称v_3 CH拉伸模式在3202和3174 cm〜（-1）处。它们全部成对出现。相对于自由分子，两个带的分量都强烈移至较低波数，这归因于两个不等价的Cu〜+吸附位点。随着C_2H_2压力的增加，位移最强的组分首先出现并获得明显更高的强度，表明它们必须对应于结合更强的位点。对代表两个乙炔在铜上吸附的乙炔的配合物的几何结构进行分析，得出铜的四重配位，包括两个氧原子和侧键结合的C_2H_2，CC键延长0.03 A，CCH角至少降低14.7。 °。由于从松弛的Cu（SII）团簇到达Cu（SII）-C_2H_2内的几何结构所需的能量，因此两种乙炔-铜配合物的计算结合能显着不同。 C_2H_2在Cu（SIII）（在超级笼壁附近的两个四元环之间的鞍座中）上的吸附比在位置II（方钠石笼的六环窗口上方）上的吸附更强。种群分析提供了向乙炔约0.14e的净电荷转移。能量分解方法证明了静电和电荷转移对Cu-沸石-乙炔相互作用能的至关重要性。谐波频率的计算表明，所有拉伸振动中位移较大的带分量必须分配给在SIII处吸附在Cu〜+上的C_2H_2，这是更稳定的位置。除了被高估的Δv_1值外，两种吸附复合物的振动频移均与实验值非常吻合。

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