Interplay between the metal-support interaction and stability in Pt/Co 3 O 4 (111) model catalysts

• Published in: Journal of materials chemistry. A, Materials for energy and sustainability Materials for energy and sustainability, 2018-11, Vol.6 (45), p.23078-23086
• Main Authors: Lykhach, Yaroslava, Faisal, Firas, Skála, Tomáš, Neitzel, Armin, Tsud, Nataliya, Vorokhta, Mykhailo, Dvořák, Filip, Beranová, Klára, Kosto, Yuliia, Prince, Kevin C., Matolín, Vladimír, Libuda, Jörg
• Format: Article
• Language: English
• ISSN: 2050-7488; 2050-7496
• DOI: 10.1039/C8TA08142E

The interplay between the metal-support interaction and stability with respect to sintering has been investigated for Pt nanoparticles supported on well-ordered Co 3 O 4 (111)/Ir(100) films in UHV and under oxidizing conditions by means of synchrotron radiation photoelectron spectroscopy (SRPES) and near ambient pressure X-ray photoelectron spectroscopy (NAP XPS). The electronic metal-support interaction between Pt and Co 3 O 4 (111) associated with charge transfer results in partial reduction of Co 3 O 4 (111) yielding partially oxidized Pt δ+ species at the interface. The stability of the supported Pt particles is coupled with the oxidation state of Pt δ+ species, which can be reduced or oxidized depending on the Pt coverage and reactive environment. Annealing of Pt/Co 3 O 4 (111)/Ir(100) in UHV triggers the reduction of Pt δ+ species. At higher temperature, reverse spillover of oxygen to the Pt nanoparticles is accompanied by reduction of Co 3 O 4 (111). Under these conditions, the oxidation state of Pt δ+ species depends strongly on Pt coverage. Thus, at low Pt coverage (0.3 ML Pt), Pt δ+ is converted to Pt 4+ , at intermediate coverage (1.3 ML Pt), Pt δ+ remains stable, and at high Pt coverage (1.93 ML), Pt δ+ is reduced to Pt 0 . Sintering of Pt particles is associated with the reduction of the Pt δ+ species. This process is prevented under oxidizing conditions due to the formation of an interfacial oxide PtO x . The formation of an interfacial PtO x is observed at 300 K under exposure to 1 × 10 −6 mbar O 2 at Pt coverages below 1.3 ML. Using NAP XPS, we observe the formation of an interfacial PtO x at high Pt coverage (2.0 ML) in an oxygen atmosphere (1 mbar) at 300 K while the formation of surface PtO x is kinetically hindered and occurs above 550 K only.