Revisiting the Evolution of IR Spectra of CO Adsorbed on Au Nanoparticles Supported on Non-reducible Supports
- PDF / 3,359,023 Bytes
- 10 Pages / 595.276 x 790.866 pts Page_size
- 8 Downloads / 176 Views
ORIGINAL PAPER
Revisiting the Evolution of IR Spectra of CO Adsorbed on Au Nanoparticles Supported on Non‑reducible Supports Ranin Atwi1 · Taha Elgayyar1 · Francisco J. Cadete Santos Aires1 · Alain Tuel1 · Frederic C. Meunier1
© Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract Gold surfaces and nanoparticles have commonly been investigated by IR spectroscopy using carbon monoxide as a molecular probe. An evolution of the IR spectra with time under CO was reported in some cases and tentatively assigned to geometrical effects (e.g. surface reconstruction or particle restructuring) or electronic effects, e.g. gold becoming negatively charged following support reduction. We report here an investigation of the evolution of the IR spectrum of CO adsorbed at 50 °C in the case of Au nanoparticles supported on non-reducible silica and alumina supports. The evolution of the carbonyl IR band signal, proposed to arise mostly from Au particle restructuring, was clearly observed. In addition, the formation of hydrogenocarbonates species on the alumina reemphasized that Au nanoparticles are somewhat active for CO dissociation via Boudouard reaction near room temperature, leading to some deposition of carbon. Water could not prevent restructuring, while O2 prevented irreversibly the reconstruction, which could even be reversed when O2 was introduced on an already restructured sample. It is hypothesized that the role of O 2 would be to remove the deposited elemental carbon that otherwise stabilize reconstructed Au. These results emphasize the complexity of the parameters affecting the restructuration of Au surfaces induced by CO and the difficulty in interpreting IR spectra of CO adsorption on Au-based materials. Graphic Abstract
Keywords Gold · Reconstruction · FT-IR · In situ · Segregation
* Frederic C. Meunier [email protected]‑lyon1.fr 1
Univ Lyon, Université Claude Bernard Lyon 1, CNRS, IRCELYON, 2 Av. Albert Einstein, 69626 Villeurbanne, France
1 Introduction The structure of nanoparticles is often modified under reaction conditions [1–4], making the use of in situ and operando methods a requirement to obtain meaningful
13
Vol.:(0123456789)
structure–activity relationships [5–8]. Au has been widely used as low-temperature CO oxidation [9–12] and water–gas shift catalyst [13, 14] and thus has been routinely investigated using CO adsorption monitored by IR spectroscopy [15–18]. Au carbonyl band positions depend on several parameters, primarily the coordination number and the oxidation state of the Au site on which CO is adsorbed. Au(111) terrace sites lead to a band at around 2130 cm−1, but, importantly, the corresponding surface coverage is essentially nil above 70 K [19]. This supports the view that on metallic particles only defect sites, such as edges and corners, are covered at and above room temperature [15, 16, 20]. Surface coverage may also affect band position, as a result of offsetting dipole coupling (blue shift) and chemical (red shift) effects [15, 17]. For inst
Data Loading...
