Spillover Reoxidation of Ceria Nanoparticles

详细信息    查看全文

• 作者：David C. Grinter ; Chris Muryn ; Alessandro Sala ; Chi-Ming Yim ; Chi L. Pang ; Tevfik O. Menteş ; Andrea Locatelli ; Geoff Thornton
• 刊名：Journal of Physical Chemistry C
• 出版年：2016
• 出版时间：May 26, 2016
• 年：2016
• 卷：120
• 期：20
• 页码：11037-11044
• 全文大小：493K
• 年卷期：0
• ISSN：1932-7455

文摘

Interest in resolving the mechanisms behind ceria’s activity has been intense due to the numerous industrial applications including those in heterogeneous catalysis. In this work, we study the reduction and reoxidation of ultrathin CeO₂(111) nanoislands on Rh(111) and Pt(111) substrates, so-called inverse model catalysts, with a combination of real and reciprocal space techniques based on X-ray photoemission electron microscopy (XPEEM) and low energy electron microscopy. Soft X-ray microfocused illumination was employed to reduce the ceria islands, which we are able to control by varying the oxygen partial pressure within the measurement chamber. Low energy electron diffraction measurements of the irradiated ceria films demonstrate the formation of an ordered array of oxygen vacancies leading to a (√7 × √7)R19.1° superstructure attributed to the ι-phase (Ce₇O₁₂)(111). Resonant photoelectron spectroscopy provides the required high sensitivity to detect small changes in Ce³⁺ concentration. The high spatial resolution of the XPEEM allows us to determine that the reduction of the ceria occurs initially at the interface of the islands with the Rh support. Reoxidation of the CeO_2–x(111) to CeO₂(111) proceeds via spillover of activated oxygen adsorbed on the Rh(111) surface as a (2 × 2) overlayer. Our results highlight the important role that the noble metal plays in the regeneration of the stoichiometric ceria surface, a vital step in many reactions on ceria. This differs from the commonly proposed Mars–van Krevelen model in which reoxidation involves direct reaction of the ceria with O₂.