ELECTRONIC-STATE AND LOCATION OF PT METAL-CLUSTERS IN KL ZEOLITE - FTIR STUDY OF CO CHEMISORPTION

Electronic state and location of Pt metal clusters supported on KL zeolite are studied by FTIR spectroscopy of adsorbed CO. Investigation of the CO adsorption was performed within the wide CO pressure range (from 4 x 10(-3) to 10(2) Pa) and supplemented by the study of the CO desorption at elevated temperature. Comparison of the data on CO adsorption and desorption at increased temperature reveals the existence of two groups of Pt particles in the sample. The first group of the particles is localized on the outer surface of the zeolite microcrystal and in the near surface region; they exhibit CO bands at 2060-2050 cm(-1) close to those of Pt supported on conventional supports. The particles of the second group are encaged inside zeolite channels and their electronic structure is presumably strongly perturbed by the zeolite framework. CO adsorbed on the Pt particles of this group exhibits coverage dependent bands at frequencies in the range 1960-1920 cm(-1). The marked downward shift of the nu CO band is attributed to the increase of electron density on these particles.