The effect of CO adsorption at room temperature on the structure of supported Pt particles

To improve the understanding of the applicability of CO-FTIR spectroscopy f or probing the electronic properties of catalysts, the effect of CO adsorpt ion on the geometry of small metal particles in Pt/LTL and Pt/SiO2 catalyst s with varying support acidities was determined by comparison of X-ray abso rption spectra before and after CO adsorption. At room temperature, the pla tinum particles (first shell coordination number N > 5) supported on SiO2 w ere stable under CO atmosphere. By contrast, the smaller platinum particles (N < 5) in zeolite LTL reconstructed with the formation of very small plat inum-CO aggregates upon admission of CO at room temperature. For both Pt/Si O2 and Pt/LTL the linear-to-bridge ratio (LB) of the CO infrared bands is a function of the support acidity/alkalinity. In the case of Pt/SiO2, the L/ B ratio directly reflects the electronic properties of the catalytically ac tive metal, since the metal particles do not reconstruct. The results show that the structure of the platinum particles in LTL zeolite, which particip ate in catalytic reactions is not the same as the Pt-CO aggregate analyzed by FTIR. Nevertheless, both the catalytic activity and L/B ratio are a func tion of support acidity.