Interaction of CO Molecules with Electron-Deficient Pt Atoms in Zeolites:  A Density Functional Model Cluster Study

Abstract

The coordination and electronic structure of monatomic Pt species in mordenite have been investigated by scalar−relativistic density functional model cluster calculations using CO molecules as a probe. It was found that anchoring a Pt−CO moiety by the protons of one or two acidic hydroxyl groups increases the CO stretching frequency compared to that of free Pt−CO, but leaves the frequency still smaller than that of a free CO molecule, in line with experiment. The results for various molecular model complexes support the hypothesis that the platinum species in mordenite are electron-deficient. An alternative model comprising “naked” protons interacting with Pt−CO moieties can be ruled out since the calculated CO frequency is too large. The dependence of the CO stretching frequency on the acidity of the Brønsted groups and on the electronic charge of the Pt species is discussed.

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.…”

The use of NaX zeolite as a template to obtain a mono-atomic pt dispersion by impregnation with Pt(II) acetylacetonate/acetone solution

“…[13][14][15][16][17][18][19] Barthoment,20 in particular, indicated the role of the aluminosilicate support in suppressing the agglomeration of metal cluster to during prolonged catalyst exploitation.…”

FTIR study of the CO adsorption over Pt/MFI catalysts: Ab initio interpretation

“…The free CO molecule was treated at the Møller–Plesset second‐order perturbation theory (MP2) and density functional theory (DFT) level with B3LYP and B3PW91 exchange‐correlation potentials. Modest LANL2DZP12 and correlation consistent aug‐cc‐pVTZ13 atomic basis sets were used on C, O, and H. The Pt atom was treated within two variants of the effective core potential (ECP) with LANL2DZP and Stuttgart group parameterization, respectively 14, 15. In both cases, conventional atomic basis sets were augmented by two sets of f ‐functions with exponential parameters 1.419 and 0.543, to improve the metal‐ligand bonding description.…”

“…This fact may be explained by a wide variety of Pt states and a great number of different bands of adsorbed CO on the Pt in the IR spectrum. Computational techniques can provide more careful analysis and interpretation of the IR spectrum of chemisorbed CO 12. The aim of the present work is to combine the experimental and theoretical approach forward to assignment and analysis of the bands in FTIR spectra of adsorbed CO over Pt‐supported catalyst.…”