Abstract
Highly dispersed Pt catalysts were prepared by deposition of Pt 4 and Pt 6 clusters, initially formed in unprotected and poly(vinyl alcohol) (PVA)-protected colloidal Pt suspensions, onto a γ-Al 2O 3 surface. These catalysts were characterized by extended X-ray absorption fine structure (EXAFS) and Fourier transform infrared (FTIR) spectroscopies. The EXAFS results indicate that the supported Pt species formed were very similar in structure to those of the original clusters in the corresponding colloidal suspensions. The FTIR results further indicate that the γ-Al 2O 3-supported Pt 4 clusters have significantly lower chemisorptive properties compared with larger supported Pt nanoparticles; nevertheless, the Pt 4/ γ-Al 2O 3 sample was active for the oxidation of CO with no need for additional activation treatment. In fact, treatment of this sample with H 2 at 150–200 °C led to the formation of Pt aggregates with sizes of 1.0–1.6 nm, demonstrating that the surface Pt 4 species readily sintered in this temperature range under reducing conditions.
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