期刊
APPLIED CATALYSIS B-ENVIRONMENTAL
卷 163, 期 -, 页码 361-369出版社
ELSEVIER
DOI: 10.1016/j.apcatb.2014.08.021
关键词
Octahedral molecular sieves; Niobium substitution; CO oxidation; DFT calculations; Fukui function f(+)
资金
- U.S. Department of Energy, Office of Basic Energy Sciences, Division of Chemical, Geochemical, and Biological Sciences [DE-FG02-86ER13622.A0000]
Framework-substituted Mn oxide octahedral molecular sieves with different Nb concentrations (2-20 mol% Nb-K-OMS-2) were synthesized via a single-step reflux method allowing for direct incorporation of the dopant into the mixed-valent Mn structure. Their specific surface areas ranged from 75 to 199 m(2) g(-1) with modified composition, size, morphology, porosity, thermal stability, and redox properties depending on the extent of substitution. Catalytic testing showed that the Nb-K-OMS-2 materials were active for CO oxidation and that the presence of Nb significantly enhanced the activity of pure K-OMS-2. For example, the conversions of 1% CO at 100 degrees C using 0%, 2%, 5%, 10%, 15%, and 20% Nb-K-OMS-2 were 4%, 10%, 25%, 62%, 59%, and 41%, respectively. When the O-2 concentrations increased from 1% to 10% at 120 degrees C, the activities of 10% and 15% Nb-K-OMS-2 materials were improved by as much as 61% and 69%, respectively. These catalysts were also stable and less prone to deactivation by moisture (similar to 3% H2O) at temperatures >100 degrees C than pure K-OMS-2. Theoretical calculations revealed that the substitution of Mn by Nb was a thermodynamically-favorable process and produced electrophilic centers, which can provide favorable sites for strong CO adsorption on the Nb-K-OMS-2 surface. The interaction of CO at these sites exhibited the beneficial effect of Nb substitution in the K-OMS-2 materials. (C) 2014 Elsevier B.V. All rights reserved.
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