Homolytic Products from Heterolytic Paths in H2 Dissociation on Metal Oxides: The Example of CeO2
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- 作者：Max Garc铆a-Melchor ; N煤ria L贸pez
- 刊名：Journal of Physical Chemistry C
- 出版年：2014
- 出版时间：May 22, 2014
- 年：2014
- 卷：118
- 期：20
- 页码：10921-10926
- 全文大小：305K
- 年卷期：v.118,no.20(May 22, 2014)
- ISSN：1932-7455
文摘
Mechanisms for H2 dissociation on metal oxides have been typically inferred from the infrared spectra of reaction products on the basis of the presence or lack of M鈥揌 fingerprints. Here, we demonstrate by means of density functional theory that oxides with polar M鈥揙 bonds might favor heterolytic dissociation. Moreover, we report that the resulting heterolytic product can further evolve to the homolytic one provided that metal ions are reducible. Hence, it follows that the redox capacity of the metal determines the reaction outcome. This finding sheds light on why both M鈥揌 and O鈥揌 bands appear in the infrared spectra of nonreducible oxides such as MgO or 纬-Al2O3, while only O鈥揌 bands are observed for reducible oxides like CeO2. It results in a unified mechanism for polar oxides that can be generalized to other materials exhibiting significant charge separation. Importantly, we also show that the low activity of CeO2 toward H2 can be improved by enhancing the basicity of surface O atoms upon lattice expansion. This may pave the way for the efficient use of CeO2 in selective hydrogenation reactions and for the further advance on processes involving dissociation of nonpolar bonds like C鈥揌.