Surface Structure Dependence of SO2 Interaction with Ceria Nanocrystals with Well-Defined Surface Facets

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• 作者：Uma Tumuluri ; Meijun Li ; Brandon G. Cook ; Bobby Sumpter ; Sheng Dai ; Zili Wu
• 刊名：Journal of Physical Chemistry C
• 出版年：2015
• 出版时间：December 31, 2015
• 年：2015
• 卷：119
• 期：52
• 页码：28895-28905
• 全文大小：682K
• ISSN：1932-7455

文摘

The effects of the surface structure of ceria (CeO₂) on the nature, strength, and amount of species resulting from SO₂ adsorption were studied using in situ IR and Raman spectroscopies coupled with mass spectrometry, along with first-principles calculations based on density functional theory (DFT). CeO₂ nanocrystals with different morphologies, namely, rods (representing a defective structure), cubes (100 facet), and octahedra (111 facet), were used to represent different CeO₂ surface structures. IR and Raman spectroscopic studies showed that the structure and binding strength of adsorbed species from SO₂ depend on the shape of the CeO₂ nanocrystals. SO₂ adsorbs mainly as surface sulfites and sulfates at room temperature on CeO₂ rods, cubes, and octahedra that were either oxidatively or reductively pretreated. The formation of sulfites is more evident on CeO₂ octahedra, whereas surface sulfates are more prominent on CeO₂ rods and cubes. This is explained by the increasing reducibility of the surface oxygen in the order octahedra < cubes < rods. Bulk sulfites are also formed during SO₂ adsorption on reduced CeO₂ rods. The formation of surface sulfites and sulfates on CeO₂ cubes is in good agreement with our DFT results of SO₂ interactions with the CeO₂(100) surface. CeO₂ rods desorb SO₂ at higher temperatures than cubes and octahedra nanocrystals, but bulk sulfates are formed on CeO₂ rods and cubes after high-temperature desorption whereas only some surface sulfates/sulfites are left on octahedra. This difference is rationalized by the fact that CeO₂ rods have the highest surface basicity and largest amount of defects among the three nanocrystals, so they bind and react with SO₂ strongly and are the most degraded after SO₂ adsorption cycles. The fundamental understanding obtained in this work on the effects of the surface structure and defects on the interaction of SO₂ with CeO₂ provides insights for the design of more sulfur-resistant CeO₂-based catalysts.