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 trans mission electron microscopy, electron diffraction, high-resolution ele ctron microscopy and Fourier-transform infrared spectroscopy. The samp les exhibit uniform dispersion of the metal phase with narrow particle size distribution. Treatment with hydrogen in the temperature range 7 73-923 K yields Pt/Si alloys at lower temperatures and platinum silici des (Pt3Si and Pt12Si5) at higher temperatures. The CO chemisorption s hows that with increasing degree of alloying (1) the nu(CO)(l) and the nu(CO)(b) band shifts to lower wavenumbers, (2) the intensity of the nu(CO)(l) band decreases and (3) the nu(CO)(b)/nu(CO)(l) intensity rat io 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.