Synthesis and characterization of γ-Al2O3-supported Pt catalysts from Pt4 and Pt6 clusters formed in aqueous solutions

Highly dispersed Pt catalysts were prepared by deposition of Pt4 and Pt6 clusters, initially formed in unprotected and poly(vinyl alcohol) (PVA)-protected colloidal Pt suspensions, onto a γ-Al2O3 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-Al2O3-supported Pt4 clusters have significantly lower chemisorptive properties compared with larger supported Pt nanoparticles; nevertheless, the Pt4/γ-Al2O3 sample was active for the oxidation of CO with no need for additional activation treatment. In fact, treatment of this sample with H2 at 150–200 °C led to the formation of Pt aggregates with sizes of 1.0–1.6 nm, demonstrating that the surface Pt4 species readily sintered in this temperature range under reducing conditions.