Journal article
Effect of dopant distribution on aging of catalytic Cr-doped transition aluminas
Bulletin of the American Physical Society, Vol.49(1)
01 Mar 2004
Abstract
Metastable (transition) aluminas, in particular gamma -Al_2O_3 and eta -Al_2O_3, are widely used as catalysts as well as supports for different transition metals. When doped with Cr, the two modifications exhibit remarkably different aging behavior: gamma -Al_2O_3-supported catalysts degrade two orders of magnitude faster than those based on eta -Al_2O_3. Here we use a combination of Z-contrast aberration-corrected scanning transmission electron microscopy (STEM), electron energy loss spectroscopy (EELS), and extended X-ray absorption fine structure (EXAFS) studies with first-principles calculations to determine the origin of this disparity. EXAFS data reveal that the coordination environments of Cr in the two forms are significantly different. STEM and EELS observations demonstrate that on gamma -Al_2O_3 Cr tends to segregate and form Cr_2O_3, while on eta -Al_2O_3 Cr is uniformly distributed. The reason for the dissimilarity, as shown by first-principles calculations, lies in the different reconstruction of the preferentially exposed 110 surface. In gamma -Al_2O_3, it serves to destabilize the catalytically active Cr sites, at the same time inducing the formation of Cr_2O_3, while in eta -Al_2O_3 Cr atoms stay dispersed on the surface and catalytically active. This work provides interesting insights in the aging behavior of transition-metal based catalysts. Authors thank Dr. Saeed Alerasool (Engelhard Corp., Beechwood, OH) for providing samples and DOE (Grants DE-AC05-00OR22725 and DE-FC02-01CH11085) and NSF (Grant DMR-0111841) for financial support.
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Details
- Title
- Effect of dopant distribution on aging of catalytic Cr-doped transition aluminas
- Creators
- Albina BorisevichSergey RashkeevSanwu WangMichael GlazoffKarl SohlbergStephen PennycookSokrates Pantelides
- Publication Details
- Bulletin of the American Physical Society, Vol.49(1)
- Resource Type
- Journal article
- Language
- English
- Academic Unit
- Chemistry
- Identifiers
- 991019222883604721