Characterization of gold(I) in NaY zeolite and acidity generation
- Hokkaido Univ., Sapporo (Japan)
Au(I) ions were incorporated into NaY zeolite via solid-vapor reaction between Au{sub 2}Cl{sub 6} vapor and partially dehydrated zeolite in high vacuum. The process involved the evolution of HCl, as monitored by temperature-programmed desorption-mass, resulting in the reduction of Au(III) into Au(I). X-ray photoelectron spectroscopy characterization of Au{sup n+}/NaY revealed the Au 4f{sub 7/2} peak exhibited a chemical shift by +1.95 eV relative to that of Au{sup 0}, implying the formation of surface AuCl or like species. Upon the introduction of Au{sub 2}Cl{sub 6} into NaY zeolite, the IR OH band at 3690 cm{sup {minus}1} due to cation-water interaction in NaY zeolite declined. On the other hand, a strong hydroxyl band at 3640 cm{sup {minus}1} was delivered due to polarization of H{sub 2}O in zeolite by the electrostatic potential associated with the Au{sup n+} (n > 1) ions. Adsorption of D{sub 2}O onto Au{sub 2}Cl{sub 6}/NaY at room temperature produced a peak at 2656 cm{sup {minus}1} due to OD species associated with Au{sup n+} (n > 1). Degassing of D{sub 2}O at 333 K reduced this peak in favor a new band at 2690 cm{sup {minus}1} which is assigned to O-D stretching mode in the Au (OD)Cl moiety. The CO chemisorption onto Au(I)/NaY at 77 K followed by evacuation to reduced pressures showed a unique carbonyl band at 2188 cm{sup {minus}1}, which is characteristic of Au(I) ions. The evolution of HCl during the solid-vapor reaction produced protonic sites, which were detected by Fourier transform infrared of pyridine adsorption. The concentration of these sites increased up to 353 K, where the solid-vapor reaction leveled off. The subsequent pyridine-Cl{sub 2} adsorption did not lead to changes in the oxidation state of Au(I) ions, indicating that NaY zeolite stabilized their structure. 37 refs., 11 figs., 1 tab.
- OSTI ID:
- 70258
- Journal Information:
- Journal of Catalysis, Vol. 152, Issue 2; Other Information: PBD: 1 Apr 1995
- Country of Publication:
- United States
- Language:
- English
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