EXAFS/XANES, XRD, and UV−Vis Characterization of Intrazeolitic Gold(I) Prepared by Monolayer Dispersion of AuCl3 inside Na−Y Zeolite

Abstract

Preparations of AuCln in Na−Y zeolite were characterized by means of X-ray diffraction (XRD), ultraviolet diffuse reflectance (UV−vis), Au LIII-edge X-ray absorption near-edge structure (XANES), and extended X-ray absorption fine structure (EXAFS). Au2Cl6 was first homogeneously dispersed on the zeolite surface by mechanical mixing at room temperature under a nitrogen atmosphere. The thermal evacuation of the mixed sample at 323 K for 72 h led to the eruption of a sole Au2Cl6 crystalline line at 2θ = 14.70° due to the condensation of the gold species on the zeolite surface. The detected Au−O bond by the EXAFS technique has a coordination distance of 2.16 A, which is about the same as that registered for the tetrameric molecule of dimethylgold(III) hydroxyl. Ramping the Au2Cl6−Na−Y reaction temperature to 338 K yielded appreciable amounts of Au(I) ions which were embedded with the Cl- ions in a (AuCl)n zig-zag-like structure. The Au−O interactions were not apparent due to the removal of OH attached to Au(I...