Oxidation of Gas-Phase and Supported Pt Nanoclusters: An Ab Initio Investigation

Abstract

Heterogeneous catalysts based on Pt nanoparticles supported on oxides are used in a number of important catalytic processes, including oxidation of hydrocarbons and redox reactions in PEM fuel cells. The interaction with gasphase oxygen is often a key component of the target chemistry and can affect the reactivity of the clusters because of their oxidation. Recent experiments have shown that the oxidation of Pt nanoparticles is influenced by a number of factors, including the clusters size and the interaction with the support, leading to properties that can differ substantially from those of larger samples. Here we combine density functional theory, the genetic algorithm, and ab initio thermodynamics to investigate the structure and the oxidizability of small Pt x (x = 1−8) nanoparticles. We find that the interaction of oxygen with Pt depends strongly on the size of the clusters, leading to facile oxidation of Pt nanoparticles. The interaction with the oxide supports studied in this work, brookite TiO 2 and Co 3 O 4 , hinders the oxidizability compared to the gas phase. At conditions of temperature and pressure typically encountered in catalytic oxidation reactions, Pt nanoparticles are predicted to be oxidized, at variance with the bulk counterpart. Our results highlight the importance of low Pt−Pt coordination in the interaction with oxygen and the role of the interaction with oxide supports.

Effects of Oxygen Adsorption on the Optical Properties of Ag Nanoparticles

“…In fact, the minimum in incremental adsorption energies (∼−1.5 eV) is reached upon completing the decoration of a whole edge, thereby contributing to the formation of two quasi-linear O–Ag–O motifs. Similar oxidized edges have been predicted and experimentally detected on stepped Pd, , Pt, AgAu, , Rh, and even Au , surfaces, and similar quasi-linear O–metal–O and angular metal–O–metal motifs have recently been identified in oxidized Pt − and Pd clusters. This suggests that the formation of such O-decorated edges is general to NPs of various transition metals and that such one-dimensional metal-oxide motifs play an important role in the chemical and physical properties of nanostructured transition metals.…”

Pd/Co3O4(111) Interface Formation

“…18−21 These parameters are particularly relevant at the nucleation stage of noble metal on reducible oxide substrates, when ultrasmall particles are particularly prone to oxidation. 21 In the present paper, we investigate the formation of the interface between Pd nanoparticles and a well-ordered Co 3 O 4 (111) substrate. The study was performed by means of DFT, synchrotron radiation photoelectron spectroscopy (SRPES), and scanning tunneling microscopy (STM).…”

“…Most often, the combination of initial state effects coupled with particle size effects and the charge transfer may result in considerable shifts of the spectral contributions rendering their binding energies similar to those typical for ionic species. Density functional theory (DFT) allows us to explore the structure, the charge transfer, and the affinity of supported noble metal clusters to form stable oxide phases. − These parameters are particularly relevant at the nucleation stage of noble metal on reducible oxide substrates, when ultrasmall particles are particularly prone to oxidation …”

CO Oxidation over Platinum Nanoclusters: Unraveling the Role of the Cluster Size and the Supporting Surface

“…On Co 3 O 4 , however, the Pt 6 cluster is bound significantly more strongly than in the case of TiO 2 . 44 This leads to a structure where the Pt atoms are more coordinated compared to Pt 6 on TiO 2 , and the incoming O 2 binds to a surface Co atom rather than to Pt, with a weak adsorption energy of −0.09 eV. In the case of Pt 1 on Co 3 O 4 , O 2 binds very strongly, with an adsorption energy of −1.88 eV (Figure 13d,e).…”