School of Environment and Energy, South China University of Technology, Guangzhou 510006, China; Department of Chemistry, University of Connecticut, Storrs, Connecticut 06269, USA; University of Chinese Academy of Sciences, Beijing 100049, China.
CAS Key Laboratory of Mineralogy and Metallogeny/Guangdong Provincial Key Laboratory of Mineral Physics and Materials, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China; University of Chinese Academy of Sciences, Beijing 100049, China.
J Environ Sci (China). 2021 Mar;101:293-303. doi: 10.1016/j.jes.2020.08.026. Epub 2020 Sep 9.
Ceria is widely used as a catalyst for soot combustion, but effects of Zr substitution on the reaction mechanism is ambiguous. The present work elucidates effects of Zr substitution on soot combustion over cubic fluorite-structured nanoceria. The nanostructured CeO, CeZrO, and CeZrO composed of 5-6 nm crystallites display T (the temperature at maximum CO yield) at 383, 355, and 375°C under 10 vol.% O/N, respectively. The size of agglomerate decreases from 165.5 to 51.9-57.3 nm, which is beneficial for the soot-ceria contact. Moreover, Zr increases the amount of surface oxygen vacancies, generating more active oxygen (O and O) for soot oxidation. Thus, the activities of CeZrO and CeZrO in soot combustion are better than that of CeO. Although oxygen vacancies promote the migration of lattice O, the enriched surface Zr also inhibits the mobility of lattice O. Therefore, the T of CeZrO is higher than that of CeZrO. Based on reaction kinetic study, soot in direct contact with ceria preferentially decomposes with low activation energy, while the oxidation of isolated soot occurs through diffusion with high activation energy. The obtained findings provide new understanding on the soot combustion over nanoceria.
氧化铈被广泛用作碳烟燃烧的催化剂，但锆取代对反应机制的影响尚不清楚。本工作阐明了锆取代对立方萤石结构纳米氧化铈上碳烟燃烧的影响。由 5-6nm 纳米晶组成的纳米结构 CeO、CeZrO 和 CeZrO 在 10vol.%O/N 下分别在 383、355 和 375°C 下显示出最大 CO 产率的温度（T）。团聚体的尺寸从 165.5nm 减小到 51.9-57.3nm，有利于碳烟与氧化铈接触。此外，Zr 增加了表面氧空位的数量，产生更多的活性氧（O 和 O）用于碳烟氧化。因此，CeZrO 和 CeZrO 在碳烟燃烧中的活性优于 CeO。尽管氧空位促进了晶格 O 的迁移，但富集的表面 Zr 也抑制了晶格 O 的迁移。因此，CeZrO 的 T 高于 CeZrO。基于反应动力学研究，与氧化铈直接接触的碳烟优先以低活化能分解，而孤立碳烟的氧化则通过具有高活化能的扩散进行。所得结果为纳米氧化铈上的碳烟燃烧提供了新的认识。
