Stability of oxidized states of freestanding and ceria-supported PtOx particles

Abstract

Nanostructured materials based on CeO2 and Pt play a fundamental role in catalyst design. However, their characterization is often challenging due to their structural complexity and the tendency of the materials to change under reaction conditions. In this work, we combine calculations based on the density functional theory, a machine-learning assisted global optimization method (GOFEE), and ab initio thermodynamics to characterize stable oxidation states of ceria-supported PtyOx particles in different environments. The collection of global minima structures for different stoichiometries resulting from the global optimisation effort is used to assess the effect of temperature, oxygen pressure, and support interactions on the phase diagrams, oxidation states, and geometries of the PtyOx particles. We thus identify favoured structural motifs and O:Pt ratios, revealing that oxidized states of free-standing and ceria-supported platinum particles are more stable than reduced ones under a wide range of conditions. These results indicate that studies rationalizing activity of ceria-supported Pt clusters must consider oxidized states, and that previous understanding of such materials obtained only with fully reduced Pt clusters may be incomplete.

Stability of PdxOy Particles Supported on Strontium Titanate Perovskite under Three-Way Catalyst Operating Conditions: Implications for Sintering Resistance

“…In the experiments, the sintering resistance is significantly improved in the oxidative atmosphere, where PGM NPs are in the oxide state rather than in the reductive atmosphere, where PGM NPs are in the metallic state. ,,,,− Nagai et al found that the sintering inhibition of Pt NPs supported on CeO 2 under the air-aging condition originates from the formation of PtO 2 NPs, where Pt–O–Ce bonds stabilize PtO 2 NPs at T = 1073 K. , Roldan Cuenya et al ,, found the enhanced stabilization of γ-Al 2 O 3 - and SnO 2 -supported Pt NPs after oxidative pretreatment, which is supposedly attributed to the formation of PtO x species with Pt–O interfacial bonds (or Pt–OH in H 2 O pretreatment) at T = 673 K. Our results are in line with recent DFT reports on Pt 13 O x on γ-Al 2 O 3 (100) and Pt 6 O x on CeO 2 (111) …”

“…Thus, the STO support stabilizes the high oxidation state of Pd, which arises from the strong interaction between PdO-like clusters and supports. ,, The stability of PdO-like clusters on the STO support in the fuel-lean and air-aging atmospheres indicates that the sintering resistance is governed by those clusters. Our results highlight the importance of the support materials in regulating the oxidation state of metal catalysts. ,, …”

“…The structures of Pd x O y clusters supported on STO surfaces were investigated using the global optimization with first-principles energy expression (GOFEE) algorithm, − which is based on the evolutionary algorithm and Gaussian process regression. The GOFEE method has been successfully applied for finding stable structures of supported metal clusters, , ultrathin oxide overlayer, and aromatic hydrocarbons supported on graphene . DFT calculations within GOFEE were performed using the grid-based projector augmented wave code with the Perdew–Burke–Ernzerhof (PBE) functional, double-ζ-polarized basis, and a grid spacing of ≈0.20 Å.…”

“…The accuracy of this approach is discussed in SI.7. This approach is also applied to find stable Pt x O y on Ce(111) and metal-embedded graphene …”

“…The accuracy of this approach is discussed in SI.7. This approach is also applied to find stable Pt x O y on Ce(111) 56 and metal-embedded graphene. 57 The binding strength of the supported Pd x O y clusters, i.e., the formation energy with respect to bulk fcc-Pd and tetragonal PdO, is calculated as…”