Metastable De-excitation Spectroscopy and Density Functional Theory Study of the Selective Oxidation of Crotyl Alcohol over Pd(111)
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- 作者：James Naughton ; Andrew Pratt ; Charles W. Woffinden ; Christopher Eames ; Steve P. Tear ; Sarah M. Thompson ; Adam F. Lee ; Karen Wilson
- 刊名：Journal of Physical Chemistry C
- 出版年：2011
- 出版时间：December 29, 2011
- 年：2011
- 卷：115
- 期：51
- 页码：25290-25297
- 全文大小：962K
- 年卷期：v.115,no.51(December 29, 2011)
- ISSN：1932-7455
文摘
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鈺怌 蟺 states. The O n and C鈺怌 蟺 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鈺怌 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 鈥渞eal-world鈥?practical chemical transformation, namely the selective oxidation of alcohols to aldehydes.