In situ coarsening study of inverse micelle-prepared Pt nanoparticles supported on -Al2O3: pretreatment and environmental effectsElectronic supplementary information (ESI) available. See DOI: 10.1039/c2cp41339f

• Main Authors: Matos, J, Ono, L. K, Behafarid, F, Croy, J. R, Mostafa, S, DeLaRiva, A. T, Datye, A. K, Frenkel, A. I, Roldan Cuenya, B
• Format: Journal Article
• Language: English
• Published: 25.07.2012
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/c2cp41339f

The thermal stability of inverse micelle prepared Pt nanoparticles (NPs) supported on nanocrystalline -Al 2 O 3 was monitored in situ under different chemical environments (H 2 , O 2 , H 2 O) via extended X-ray absorption fine-structure spectroscopy (EXAFS) and ex situ via scanning transmission electron microscopy (STEM). Drastic differences in the stability of identically synthesized NP samples were observed upon exposure to two different pre-treatments. In particular, exposure to O 2 at 400 °C before high temperature annealing in H 2 (800 °C) was found to result in the stabilization of the inverse micelle prepared Pt NPs, reaching a maximum overall size after moderate coarsening of 1 nm. Interestingly, when an analogous sample was pre-treated in H 2 at 400 °C, a final size of 5 nm was reached at 800 °C. The beneficial role of oxygen in the stabilization of small Pt NPs was also observed in situ during annealing treatments in O 2 at 450 °C for several hours. In particular, while NPs of 0.5 ± 0.1 nm initial average size did not display any significant sintering (0.6 ± 0.2 nm final size), an analogous thermal treatment in hydrogen leads to NP coarsening (1.2 ± 0.3 nm). The same sample pre-dosed and annealed in an atmosphere containing water only displayed moderate sintering (0.8 ± 0.3 nm). Our data suggest that PtO x species, possibly modifying the NP/support interface, play a role in the stabilization of small Pt NPs. Our study reveals the enhanced thermal stability of inverse micelle prepared Pt NPs and the importance of the sample pre-treatment and annealing environment in the minimization of undesired sintering processes affecting the catalytic performance of nanosized particles. The enhanced thermal stability of Pt nanoparticles after pre-treatments in oxygen is demonstrated. Lower stability against sintering was observed in H 2 and H 2 O environments.