Transient Structures of PdO during CO Oxidation over Pd(100)

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• 作者：Mikhail Shipilin ; Johan Gustafson ; Chu Zhang ; Lindsay R. Merte ; Andreas Stierle ; Uta Hejral ; Uta Ruett ; Olof Gutowski ; Magnus Skoglundh ; Per-Anders Carlsson ; Edvin Lundgren
• 刊名：Journal of Physical Chemistry C
• 出版年：2015
• 出版时间：July 9, 2015
• 年：2015
• 卷：119
• 期：27
• 页码：15469-15476
• 全文大小：371K
• ISSN：1932-7455

文摘

In situ high-energy surface X-ray diffraction was employed to determine the surface structure dynamics of a Pd(100) single crystal surface acting as a model catalyst to promote CO oxidation. The measurements were performed under semirealistic conditions, i.e., 100 mbar total gas pressure and 600 K sample temperature. The surface structure was studied in detail both in a steady gas flow and in a gradually changing gas composition with a time resolution of 0.5 s. The experimental technique allows for rapid reciprocal space mapping providing the complete information on structural changes of a surface with unprecedented time resolution in harsh conditions. Our results show that the (鈭? 脳 鈭?)R27掳-PdO(101) surface oxide forms in a close to stoichiometric O₂ and CO gas mixture as the mass spectrometry indicates a transition to a highly active state with the reaction rate limited by the CO mass transfer to the Pd(100) surface. Using a low excess of O₂ in the gas stoichiometry, islands of bulk oxide grow epitaxially in the same (101) crystallographic orientation of the bulk PdO unit cell according to a Stranski鈥揔rastanov type of growth. The morphology of the islands is analyzed quantitatively. Upon further increase of the O₂ partial pressure a polycrystalline Pd oxide forms on the surface.