In situ ESR study of gold supported on NaY zeolite

Abstract

Electron spin resonance (ESR) spectroscopy was used to study the anchoring of a Au complex and gold nanoparticles in NaY type zeolites. The complex of Au(II) with two nitrogen atoms of two ethylenediamine ligands [g iso = 2.053, A (Au) = 16.4 G, A (N) = 15.0 G.] in the supercage of the zeolite and conduction electron spin resonance (CESR) of gold particles with 1.56-nm diameter (g = 2.064) were observed. Their formation and stability were related with the gold concentration and the pre-treatment conditions. The small gold particles stabilized in the supercage of zeolite were formed in the samples with low gold concentration after oxygen pre-treatment. The confinement in the zeolite pores obviously prevents the Au(II) complex bound to two nitrogen ligands from undergoing disproportionation.

NMR study of Au/Al nanosytems in solution

“…The spectra of all samples contain signal with g = 2.062 regardless of a preparation route. This signal is also reported in a number of papers [13,15,27], in particular the EPR spectra measured at low temperatures contain a distinct fine structure observed on the EPR spectra of our samples. We associate the origin of this signal with the paramagnetic state of the reduced 5d 10 6s 1 gold in the nanoparticle with an odd number of atoms.…”

“…The g = 2.17 signal is reported by other researchers [13,15] and is often attributed to the formation of the intermediate incompletely reduced paramagnetic state of Au 2+ corresponding to [Xe]4f 14 5d 9 electron configuration. The g = 2.17 signal appearance is mostly coupled with the registration of g = 2.0048 signal (Fig.…”

“…In contrast, the authors studied the stabilization of the gold containing nanoparticles at the zeolite surface [15] did not reveal the narrow line with g = 2.0048 . This line is also absent on the spectra of the other our samples fabricated by vaporization and salting out of the stoichiometric solution in dioxane (Fig.…”

“…The general model of the orbital origin of the paramagnetic properties of the ensemble of gold nanoparticles was considered in [28]. The fine structure is attributed to quantum confinement of the nanoparticle electron structure [15,29], which is predicted theoretically [30].…”

“…Methods of the synthesis of the gold nanoparticles are based on the multistage reduction process of Au 3+ −→ Au 0 , which a priori does not suggest any paramagnetic properties provided it deals with a bulk material. However, there are a set of experimental evidences of the paramagnetism in gold-containing nanoparticles [13][14][15] as well as nanoparticles or metal complexes containing atoms-diamagnetics in the bulk such as silver [16] and copper [17].…”