Identification of isolated Pt atoms in H-mordenite

Abstract

The state and dispersion of Pt supported on mordenite have been studied using FTIR spectroscopy, CO chemisorption, and H-D isotope exchange of cyclopentane. Under conditions for which other criteria indicate the presence of monatomic Pt' , a characteristic IR band of adsorbed CO is identified at 2123 cm-'. The position of this band does not change with CO coverage, indicating an interaction between CO and highly dispersed Pt. A significant blue shift of the band with respect to that of CO on multiatomic Pt clusters and the disappearance of this band upon neutralizing the acidic OH groups show that the Pt atoms are electron-deficient and interact with zeolite protons. These FTIR data thus confirm the presence of extremely small Pt clusters, presumably [Pt,-H,]' + adducts, in H-mordenite.

Transition metal clusters and supported species with metal–carbon bonds from first-principles quantum chemistry

“…That frequency shift was attributed to a negative charge of the encapsulated platinum cluster, in good agreement with the above mentioned correlation [17]. Note that combination of DF results [53] and vibrational spectroscopy data for CO adsorption complexes with Pt species in mordenite, assigned to be as small as monatomic moieties [54] turned out to be electron-deficient.…”

Structure and Reactivity of Small Metallic and Bimetallic Clusters Hosted in Molecular Sieves

“…These data also showed that the CO frequency alone cannot be a criterion for distinguishing between single atoms and ions. The same "magic" frequency 2123 em -1 was found for non-reduced Pt and fully reduced Pt in ZSM-5 and for reduced Pt in mordenite [28]. This formal coincidence is explained by the significant electron-deficiency of metal atoms in zeolites due to their interaction with protons [3,28].…”

The State and Reactivity of Pt6 Particles in ZSM-5 Zeolite

“…This observation can be interpreted as due to the electron transfer from the metal particle to the neighboring Brønsted acid site [17]. The electron deficiency of metal particles is also supported by the frequency shift in the infrared spectra of adsorbed CO [18][19][20].…”