Key Role Played by Metallic Nanoparticles on the Ceria Reduction

Abstract

In this work, the reduction properties of ceria (CeO2) used as support of metallic nanoparticles (Au, Pd, Au0.9Pd0.1, and Au0.8Pt0.2) were elucidated. The catalysts were exposed to a reduction treatment in H2 atmosphere at 500 °C. In situ X-ray absorption spectroscopy (in situ XAS) and in situ time-resolved XAS measurements at the Ce L3 edge were used to probe the local atomic order around Ce atoms and the Ce oxidation state. In this way, it was observed that the supported metallic nanoparticles improve the reduction process of the support. Moreover, the reduction of ceria is dependent on the composition of the metallic nanoparticle supported. By means of in situ XAS measurements at the Au and Pt L2,3 edges, it was possible to obtain information concerning the fractional change in the number of 5d-band electron holes relative to a reference material for the Au- and Pt-containing nanoparticles. In this way, it was observed as evidence for the charge transfer effect from the nanoparticles to the support, which is responsible for the improved reduction of the CeO2 support in the presence of nanoparticles. This result is corroborated by the observation of energy shifts on the Au 4f, Pd 3d, and Pt 4f binding energy values of the measured X-ray photoelectron spectroscopy (XPS) spectra. In this way, this work contributes to elucidating the physical mechanisms responsible for the enhanced support reduction effect existing in modern ceria-based catalyst.

Effect of Pr on the electrical and chemical properties of cerium oxide prepared by combustion method

“…Comparing the spectral components of the cerium and the praseodymium in the two samples, it was evidenced that the binding energies present a chemical shift when the concentration of praseodymium in the cerium dioxide increases because the modification of Ce 4+ ions by Pr 3+ ions creates an flow in charge density generating an expansion of the unit cell and the lattice parameters, corroborating the Rietveld refinement analysis of the two systems . In this way, although the binding energies of the cerium and praseodymium ions of the Ce 0.2 Pr 0.8 O 2 sample are slightly higher, since the modification of the local chemical environment of the atoms induces a shielding effect which is observed in the positive chemical shifts shown in the XPS spectra, these chemical shift are not significant (<1 eV) due to the small difference in electronegativity of the cerium and praseodymium atoms …”

Enhanced photocatalytic reduction of 4‐nitrophenol over Ir/CeO2 photocatalysts under UV irradiation

“…[41][42][43] It is well known that the presence of oxidized metal particles could occur by the electronic transfer between the partially reduced CeO 2 and metal particles. 44…”

Reduction‐Driven 3D to 2D Transformation of Cu Nanoparticles

“…[ 9,18 ] Although the observation of a small change on the Cu compound fractions between the samples, the estimated charge transfer amount from Au‐based nanoparticles of similar size to CeO 2 is also small. [ 24 ] The results show that the Cu and Ce oxidation states can be controlled by the synthesis procedure of CeO 2‐ x nanoparticles. It is interesting to observe that James et al.…”