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Structure–activity correlations in thin film model catalysts: CO hydrogenation on Rh/VOx: Part I. The morphology, composition and structure of vanadia-supported and -promoted Rh particles upon oxidation and reduction

Paper ID Volume ID Publish Year Pages File Format Full-Text
44296 46014 2006 12 PDF Available
Title
Structure–activity correlations in thin film model catalysts: CO hydrogenation on Rh/VOx: Part I. The morphology, composition and structure of vanadia-supported and -promoted Rh particles upon oxidation and reduction
Abstract

The combination of (high-resolution) electron microscopy and electron diffraction was applied to study the structural and morphological alterations of a number of Rh/VOx-model systems upon oxidation and reduction, and to discriminate between different phenomena of metal–support interaction. Well-defined Rh particles (mean size 10–15 nm) were grown epitaxially on NaCl(0 0 1) surfaces and subsequently covered by layers of VOx of varying thickness (0.07–25 nm), prepared by reactive deposition of V metal in 10−2 Pa O2. Most films were covered with a stabilizing layer of amorphous alumina. The resulting model catalysts were subjected to an oxidative treatment at 673 K in O2 for 1 h and to subsequent reduction in the temperature range 373–873 K.While higher VOx exposures (mean VOx coverage ≥ 3 nm) favour the formation of crystalline V2O3 phases in partial epitaxial orientation to the Rh particles in the as-deposited state, lower exposures result in less ordered layers of cubic VO. Similarly, after a treatment in 1 bar O2 at 673 K the oxidation states of vanadium vary between V5+ and V2+, depending on the film thickness.Decoration of Rh by reduced VOx species was found to be the dominant feature of metal–support interaction upon reduction at low temperatures (T < 573 K), whereas at increasing reduction temperature the formation of distinct Rh–V alloys (V3Rh5, Rh3V, V3Rh and VRh, respectively) was observed. On a “VOx/Rh/Al2O3” catalyst, prepared by depositing 1ML VOx prior to Rh deposition alloy formation was not detected, and decoration of the metal particles was the dominant effect of reduction at 673 K. A counterpart to Rh/V “subsurface” or “surface” alloys, known to be formed on bulk Rh surfaces under similar conditions, could not be observed.

Keywords
Metal–support interaction; Rhodium; Vanadium; Alloy formation; Electron microscopy; Selected area electron diffraction
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Structure–activity correlations in thin film model catalysts: CO hydrogenation on Rh/VOx: Part I. The morphology, composition and structure of vanadia-supported and -promoted Rh particles upon oxidation and reduction
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Publisher
Database: Elsevier - ScienceDirect
Journal: Applied Catalysis A: General - Volume 308, 10 July 2006, Pages 31–42
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Catalysis
Get Full-Text Now
Don't Miss Today's Special Offer
Price was $35.95
You save - $31
Price after discount Only $4.95
100% Money Back Guarantee
Full-text PDF Download
Online Support
Any Questions? feel free to contact us