State Key Laboratory of Surface Physics, Physics Department, Fudan University, Shanghai 200433, China.
Key Laboratory of Micro and Nano Photonic Structures, Fudan University, Shanghai 200433, China.
Proc Natl Acad Sci U S A. 2018 Apr 24;115(17):E3888-E3894. doi: 10.1073/pnas.1802741115. Epub 2018 Apr 9.
The facet-specific interaction between molecules and crystalline catalysts, such as titanium dioxides (TiO), has attracted much attention due to possible facet-dependent reactivity. Using surface-sensitive sum-frequency vibrational spectroscopy, we have studied how methanol interacts with different common facets of crystalline TiO, including rutile(110), (001), (100), and anatase(101), under ambient temperature and pressure. We found that methanol adsorbs predominantly in the molecular form on all of the four surfaces, while spontaneous dissociation into methoxy occurs preferentially when these surfaces become defective. Extraction of Fermi resonance coupling between stretch and bending modes of the methyl group in analyzing adsorbed methanol spectra allows determination of the methanol adsorption isotherm. The isotherms obtained for the four surfaces are nearly the same, yielding two adsorbed Gibbs free energies associated with two different adsorption configurations singled out by ab initio calculations. They are () ∼-20 kJ/mol for methanol with its oxygen attached to a low-coordinated surface titanium, and () ∼-5 kJ/mol for methanol hydrogen-bonded to a surface oxygen and a neighboring methanol molecule. Despite similar adsorption energetics, the Fermi resonance coupling strength for adsorbed methanol appears to depend sensitively on the surface facet and coverage.
分子与结晶催化剂（如二氧化钛（TiO））之间的特定晶面相互作用因其可能的晶面依赖反应性而引起了广泛关注。使用表面敏感的和频振动光谱，我们在环境温度和压力下研究了甲醇与结晶 TiO 的不同常见晶面（包括金红石(110)、(001)、(100)和锐钛矿(101)）之间的相互作用。我们发现甲醇在所有四个表面上主要以分子形式吸附，而当这些表面出现缺陷时，甲醇会自发地离解成甲氧基。通过分析吸附甲醇光谱中的伸缩和弯曲模式之间的费米共振耦合，提取出了甲醇吸附等温线。对于四个表面得到的等温线几乎相同，通过从头计算确定了两个与两种不同吸附构型相关的吸附吉布斯自由能。其中一个是（）∼-20 kJ/mol，甲醇的氧与低配位的表面钛相连；另一个是（）∼-5 kJ/mol，甲醇与表面氧和相邻甲醇分子形成氢键。尽管吸附能相似，但吸附甲醇的费米共振耦合强度似乎对表面晶面和覆盖率敏感。
