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Evidence for an active oxygen species on Au/TiO2(1 1 0) model catalysts during investigation with in situ X-ray photoelectron spectroscopy

Paper ID Volume ID Publish Year Pages File Format Full-Text
55434 47053 2012 6 PDF Available
Title
Evidence for an active oxygen species on Au/TiO2(1 1 0) model catalysts during investigation with in situ X-ray photoelectron spectroscopy
Abstract

The influence of oxygen (O2) and carbon monoxide (CO) on Au nanoparticles supported on TiO2(1 1 0) in the size range of 2–3 nm has been studied using X-ray photoelectron spectroscopy (XPS) and in situ (high pressure) XPS at 300 K for O2 and/or CO pressures of 0.1–1 mbar. These experiments were aimed at revisiting Au 4f core level shifts as reported in the literature and most importantly, to establish the dependence of the core-level shifts on the knowledge that there exists a maximum in reactivity for CO oxidation. Two samples were prepared with a coverage corresponding to that maximum (Au coverage 0.14–0.2 ML, particle size estimated to ∼2–2.5 nm) while a third sample was expected to be less reactive (Au coverage 0.4 ML, particle size estimated to ∼3.3 nm). At elevated O2 pressures, a new Au 4f component at higher binding energy (2.4–2.6 eV relative to the Au(0) bulk signal) evolved at all particle sizes. Its appearance was attributed to a radiation-induced activation of oxygen and simultaneous oxidation of gold. The activation was much more efficient on the ∼2–2.5 nm particles. The relative intensity of the oxide component depended strongly on O2 pressure and, thus, on the equilibrium coverage of O2. While not present in 0.1 mbar O2 regardless of exposure time and particle size, it dominated the Au 4f spectrum of particles ∼2–2.5 nm in size at 1 mbar oxygen pressure. This pressure-dependent formation reconciles previously conflicting XPS data. Finally, the activated oxygen species were very reactive toward CO as manifested by the rapid disappearance of the new Au 4f component in a 1:1 mixture of CO and O2. The rates of evolution and consumption of this component were found to depend on gold coverage (and thus, particle size) and were highest for the smaller particles.

Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (160 K)Download as PowerPoint slideHighlights► Au/TiO2(1 1 0) planar model catalysts for CO oxidation. ► In situ X-ray photoelectron spectroscopy in O2 and O2/CO mixtures. ► Au 4f shifts smaller than 1 eV suggest transient molecular adsorption of O2. ► X-ray induced formation of gold oxide evidenced by Au 4f shift larger than 2 eV. ► Gold oxide reacts with CO.

Keywords
Catalysis; In situ photoelectron spectroscopy; Gold; Titania; Carbon monoxide; Oxygen; Oxidation
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Evidence for an active oxygen species on Au/TiO2(1 1 0) model catalysts during investigation with in situ X-ray photoelectron spectroscopy
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Publisher
Database: Elsevier - ScienceDirect
Journal: Catalysis Today - Volume 181, Issue 1, 12 February 2012, Pages 20–25
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