Effect of preparation technique on the properties of platinum in NaY zeolite: A study by FTIR spectroscopy of adsorbed CO

Two platinum-containing zeolites were studied by XPS, TPR and IR spectroscopy of adsorbed CO. The sample Pt–NaY was prepared by ion-exchange and the Pt/NaY sample, by impregnation. XP spectra indicate a higher heterogeneity of platinum on the impregnated sample and enrichment of its outer surface in platinum, compared to the exchanged sample. Accessible platinum in both activated samples is in the form of metal. However, oxidation of Pt–NaY with a NO + O2 mixture results in creation of cationic sites. Adsorption of CO on the sample thus treated leads to formation of different platinum carbonyls: (i) Pt3+(CO)2 species (2204 and 2168 cm−1) which are decomposed without production of monocarbonyls, (ii) two kinds of Pt2+–CO species (2155 and 2141 cm−1), (iii) Pt+(CO)2 dicarbonyls (2127 and 2091 cm−1) and (iv) linear Pt0–CO species (2080–2054 cm−1). In contrast, almost no cationic sites were produced after the attempts to oxidize the impregnated sample. In both samples Chini-complexes were formed after interaction with CO at 373 K. However, the process was much easier with the impregnated sample. This indicates that exchanged cations, interacting more strongly with the zeolite matrix, are not suitable for preparation of anionic carbonyls. The effect of the preparation technique is discussed and the results are compared with the results on platinum in other zeolites.

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