Abstract
This review focuses on the chemical methods used to prepare supported bimetallic heterogeneous catalysts, i.e., bimetallic nanoparticles deposited on a support. The review is limited to the preparation of gold-based bimetallic catalysts and moreover to bimetallic nanoparticles supported on powder inorganic supports, i.e., on the surface or in the porosity, and not on model supports such as single crystals.
Highlights
In the field of heterogeneous catalysis, which involves the use of solid materials as catalysts for gas phase reactions and for some liquid phase reactions, metal catalysts constitute an important class of catalysts
Regarding the characterization of the bimetallic nanoparticles, many techniques can be used, from classical and simple ones, such as X-ray diffraction (XRD), that can provide an overall rough view of the bimetallic character provided that the particles are large enough and that the lattice parameters of the two metals are different enough, to more sophisticated techniques, such as X-ray photoelectron spectroscopy (XPS) thanks to binding energy (BE) shifts that may attest for charge transfer between two metals, UV-visible spectroscopy able to show possible shifts and shape changes of the gold plasmon band, IR spectroscopy coupled with the adsorption of CO as probe molecules (CO-FTIR and CO-DRIFTS), and X-ray absorption fine structure spectroscopy (XAFS); some catalytic reactions can be used to characterize indirectly the samples
After electroless deposition (ED) completion and thorough washing, EDS, CO-DRIFTS, and XPS characterization showed that the particles were bimetallic; the results showed that the coverage of Pd by Au could be controlled by the amount of gold in the ED solution
Summary
In the field of heterogeneous catalysis, which involves the use of solid materials as catalysts for gas phase reactions and for some liquid phase reactions, metal catalysts constitute an important class of catalysts. Regarding the characterization of the bimetallic nanoparticles, many techniques can be used, from classical and simple ones, such as X-ray diffraction (XRD), that can provide an overall rough view of the bimetallic character provided that the particles are large enough and that the lattice parameters of the two metals are different enough, to more sophisticated techniques, such as X-ray photoelectron spectroscopy (XPS) thanks to binding energy (BE) shifts that may attest for charge transfer between two metals, UV-visible spectroscopy able to show possible shifts and shape changes of the gold plasmon band, IR spectroscopy coupled with the adsorption of CO as probe molecules (CO-FTIR and CO-DRIFTS), and X-ray absorption fine structure spectroscopy (XAFS); some catalytic reactions can be used to characterize indirectly the samples. All these techniques provide an overview of the bimetallic character of the nanoparticles, but the various techniques of electron microscopy with aberration corrections, high resolution transmission electron microscopy (HRTEM) or scanning transmission electron microscopy (STEM), energy-dispersive X-ray spectroscopy (EDX or EDS), high angle annular dark field imaging (HAADF) and electron energy loss spectroscopy (EELS), can bring information on individual particles, in ultra high vacuum (UHV) and under controlled atmosphere
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