Metastable De-excitation Spectroscopy and Density Functional Theory Study of the Selective Oxidation of Crotyl Alcohol over Pd(111)
Metastable De-excitation Spectroscopy and Density Functional Theory Study of the Selective Oxidation of Crotyl Alcohol over Pd(111)
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DOI：
10.1021/jp205340z
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发表时间：
2011-12
影响因子：
3.7
通讯作者：
J. Naughton;A. Pratt;C. Woffinden;C. Eames;C. Eames;S. Tear;S. Thompson;A. Lee;K. Wilson
中科院分区：
文献类型：
--
作者：
J. Naughton;A. Pratt;C. Woffinden;C. Eames;C. Eames;S. Tear;S. Thompson;A. Lee;K. Wilson
亚稳态去激发光谱 (MDS) 的极其表面敏感技术已被用来探测巴豆醇在 Pd(111) 上的键合和反应性，并深入了解巴豆醛的选择性氧化途径。亚稳态 He (23S) 原子的俄歇去激发 (AD) 揭示了与吸附醇的分子轨道相关的独特特征，对应于烃骨架的发射、O n 非键合和 C=C π 态。与醛相比，醇的 O n 和 C=C π 态相反。醇的密度泛函理论 (DFT) 计算表明，在基板温度低于 200 K 时，C=C 和 O 键与表面平行排列的吸附模式在能量上受到青睐。此类配置的态密度计算与实验 MDS 测量结果非常一致。 MDS 揭示了巴豆醇在 200 至 250 K 之间氧化脱氢为巴豆醛，导致小峰向更高结合能移动。根据游离分子的 DFT 和 UPS 研究，分子内变化导致醇中前两个 MO 与醛中的前两个 MO 的分配相反。随后的巴豆醛脱羰和相关的丙啶形成（高于 260 K）也可以通过 MDS 和补充理论计算确定为失活和选择性损失的根源。以这种方式结合 MDS 和 DFT 代表了一种阐明与“现实世界”实际化学转化（即醇选择性氧化为醛）相关的表面催化反应途径的新方法。
The extremely surface sensitive technique of metastable de-excitation spectroscopy (MDS) has been utilized to probe the bonding and reactivity of crotyl alcohol over Pd(111) and provide insight into the selective oxidation pathway to crotonaldehyde. Auger de-excitation (AD) of metastable He (23S) atoms reveals distinct features associated with the molecular orbitals of the adsorbed alcohol, corresponding to emission from the hydrocarbon skeleton, the O n nonbonding, and C═C π states. The O n and C═C π states of the alcohol are reversed when compared to those of the aldehyde. Density functional theory (DFT) calculations of the alcohol show that an adsorption mode with both C═C and O bonds aligned somewhat parallel to the surface is energetically favored at a substrate temperature below 200 K. Density of states calculations for such configurations are in excellent agreement with experimental MDS measurements. MDS revealed oxidative dehydrogenation of crotyl alcohol to crotonaldehyde between 200 and 250 K, resulting in small peak shifts to higher binding energy. Intramolecular changes lead to the opposite assignment of the first two MOs in the alcohol versus the aldehyde, in accordance with DFT and UPS studies of the free molecules. Subsequent crotonaldehyde decarbonylation and associated propylidyne formation above 260 K could also be identified by MDS and complementary theoretical calculations as the origin of deactivation and selectivity loss. Combining MDS and DFT in this way represents a novel approach to elucidating surface catalyzed reaction pathways associated with a “real-world” practical chemical transformation, namely the selective oxidation of alcohols to aldehydes.