Influence of the strong metal-support interaction on the CO chemisorption at a Pt/SiO2 catalyst

Pt/SiO2 catalysts prepared by sol-gel processing were studied by transmission electron microscopy, electron diffraction, high-resolution electron microscopy and Fourier-transform infrared spectroscopy. The samples exhibit uniform dispersion of the metal phase with narrow particle size distribution. Treatment with hydrogen in the temperature range 773-923 K yields Pt/Si alloys at lower temperatures and platinum silicides (Pt3Si and Pt12Si5) at higher temperatures. The CO chemisorption shows that with increasing degree of alloying (1) the ν (CO)l and the ν (CO)b band shifts to lower wavenumbers, (2) the intensity of the ν (CO)l band decreases and (3) the ν (CO)b/ν(CO)l intensity ratio increases. The phenomena are interpreted by simultaneous effects of Pt surface dilution, enhanced electron back-donation from platinum to CO and Pt d-band narrowing.