Density Functional Theory Study of the Mechanism of Formaldehyde Oxidation on Mn-Doped Ceria

详细信息    查看全文

• 作者：Hairong Wu ; Sicong Ma ; Weiyu Song ; Emiel J. M. Hensen
• 刊名：Journal of Physical Chemistry C
• 出版年：2016
• 出版时间：June 23, 2016
• 年：2016
• 卷：120
• 期：24
• 页码：13071-13077
• 全文大小：452K
• 年卷期：0
• ISSN：1932-7455

文摘

Formaldehyde is an indoor pollutant, whose removal under mild conditions is of growing importance. Mn-doped CeO₂ is a promising catalyst for the oxidation of formaldehyde to water and carbon dioxide. We have theoretically investigated the origin of the high activity of Mn-doped ceria as compared with ceria. DFT+U calculations were used to identify adsorption modes and compare different reaction mechanisms. The reaction mechanism involves HCHO adsorption, two C–H bond cleavage steps involving reactive O atoms (either structural O atoms of the support or adsorbed O₂), H₂O formation, and H₂O and CO₂ desorption. On the stoichiometric surface, a Mars–Van Krevelen mechanism occurs, which involves ceria surface O atoms. The lower coordination number of these O atoms in the stoichiometric Mn-doped ceria results in decreased barriers for C–H bond cleavage. In the presence of defects which will be ubiquitous in the Mn-doped surface, a Langmuir–Hinshelwood mechanism becomes feasible, as O₂ can strongly adsorb on the oxygen vacancy next to Mn where HCHO adsorbs. The adsorbed O₂ molecule is strongly activated by the reduced ceria surface. The barriers for C–H cleavage are lowest for reactions involving adsorbed O₂. We predict that the HCHO oxidation reaction proceeds with the lowest overall barrier on the defective Mn-doped CeO₂ surface.