Metal–Support Interaction and Charge Distribution in Ceria-Supported Au Particles Exposed to CO

Abstract

Understanding how reaction conditions affect metal–support interactions in catalytic materials is one of the most challenging tasks in heterogeneous catalysis research. Metal nanoparticles and their supports often undergo changes in structure and oxidation state when exposed to reactants, hindering a straightforward understanding of the structure–activity relations using only ex situ or ultrahigh vacuum techniques. Overcoming these limitations, we explored the metal–support interaction between gold nanoparticles and ceria supports in ultrahigh vacuum and after exposure to CO. A combination of in situ methods (on powder and model Au/CeO 2 samples) and theoretical calculations was applied to investigate the gold/ceria interface and its reactivity toward CO exposure. X-ray photoelectron spectroscopy measurements rationalized by first-principles calculations reveal a distinctly inhomogeneous charge distribution, with Au + atoms in contact with the ceria substrate and neutral Au 0 atoms at the surface of the Au nanoparticles. Exposure to CO partially reduces the ceria substrate, leading to electron transfer to the supported Au nanoparticles. Transferred electrons can delocalize among the neutral Au atoms of the particle or contribute to forming inert Au δ− atoms near oxygen vacancies at the ceria surface. This charge redistribution is consistent with the evolution of the vibrational frequencies of CO adsorbed on Au particles obtained using diffuse reflectance infrared Fourier transform spectroscopy.

In Situ Spectroscopy and Microscopy Insights into the CO Oxidation Mechanism on Au/CeO2(111)

“…However, still high RER at elevated temperatures, indicating a significant amount of Ce 3+ ions on the surface, suggests that they are rather formed at the interface perimeter, which enables detection by SRPES. This observation was pointed out by recent theoretical calculations showing the formation of Ce 3+ cations at the periphery of Au NPs …”

Hierarchical Au/CeO2systems – influence of Ln3+dopants on the catalytic activity in the propane oxidation process

“…The decoration process of the pure and Ln-doped hierarchical ceria tube-like macroparticles by gold nanoparticles was performed by the deposition-precipitation method. 60 As shown in the literature [86][87][88][89] and our previous experiences, 61,90 the decoration method used in this work is effective in obtaining ceria (or defected ceria) with small gold nanocrystals well dispersed on the surface (with various support morphologiescubes, octahedra, rods, etc.). However, the above information concerns rather large CeO 2 crystallites with often defined morphology (flat surfaces).…”

“…As is known, in many catalytic processes involving Au/CeO 2 materials, active centres located at the Au/CeO 2 / atmosphere interface are responsible for the catalytic activity. 89,91,92 Fig. 2 shows the XRD patterns of the decorated hierarchical, tube-like, ceria-based supports.…”

Room-Temperature CO Oxidation over Au–Pd Monometallic and Bimetallic Nanoparticle-Supported MgO

“…The former peak is deconvoluted into two sharp peaks at around 87.1 and 88.5 eV, in addition to another weak broad peak at 85.6 eV. Accordingly, two kinds of Au species on the catalyst surface could be identified, the first state is Au 0 (63.2 at %) as evident by the XPS peaks at around 83.5 and 87.1 eV, and the second state is the oxidized Au + species (36.8 at %) due to the XPS doublet peak at around 85.6 and 88.5 eV. − Moreover, the Au4 f XPS peaks are moved to greater binding energies as the Pd content increases, which may be credited to the charge transfer among Au and Pd atoms . Another peak at 91.5 eV (49.3 at %) is observed for the 0.5Au0.5PdMgO catalyst, which could be assigned to Au/Pd alloy formation on the surface (Figure b), while the ratio of Au 0 and Au + is decreased to 29.1 and 21.6 at %, respectively.…”