Surface Diffusion of Pt Clusters in/on SiO2 Matrix at Elevated Temperatures and Their Improved Catalytic Activities in Benzene Oxidation

Pt in/on silica nanoparticles were synthesized by flame spray pyrolysis (FSP) followed by H-2 reduction at different temperature and tested in benzene complete oxidation reaction. The Pt clusters diffusion from the interior to the exterior of the SiO2 matrix followed by aggregation in/on the SiO2 matrix was observed with elevated temperature (3001100 degrees C) and time (05 h). The aggregation of the Pt clusters on the surface of the SiO2 matrix was also evidenced by X-ray diffraction (XRD), transmission electron microscopy (TEM), and CO-pulse chemisorption. The effect of heat treatment temperature and time on the Pt/SiO2 structure was discussed. In combination with the experimental study, a further physical model describing the structural transformation was developed to complementarily depict the diffusion and aggregation process. The developed physical model correlated well with the experimental data. The catalytic activities increased with the elevated temperature until Pt3Si species was present at 1100 degrees C. The improved catalytic activities were attributed to the structural transformation induced by the elevated temperature. The rate of the Pt clusters diffusion to the surface and aggregation on the surface determined the Pt dispersion, which is the key mechanism in determining the catalytic activity.