Supported Au Catalysts Prepared from Au Phosphine Complexes and As-Precipitated Metal Hydroxides: Characterization and Low-Temperature CO Oxidation
✍ Scribed by Youzhu Yuan; Anguelina P. Kozlova; Kiyotaka Asakura; Huilin Wan; Khirui Tsai; Yasuhiro Iwasawa
- Publisher
- Elsevier Science
- Year
- 1997
- Tongue
- English
- Weight
- 267 KB
- Volume
- 170
- Category
- Article
- ISSN
- 0021-9517
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✦ Synopsis
Supported Au catalysts were prepared by attaching Au phosphine complexes, Au(PPh 3 )(NO 3 ) (1) and [Au 9 (PPh 3 ) 8 ](NO 3 ) 3 (2), on as-precipitated metal hydroxides M(OH) *
x ( * , as-precipitated; M = Mn 2+ , Co 2+ , Fe 3+ , Ni 2+ , Zn 2+ , Mg 2+ , Cu 2+ , Ti 4+ , Ce 4+ , and La 3+ ), followed by temperature-programmed calcination in a flow of dry air. The obtained Au catalysts showed high catalytic activities in low-temperature CO oxidation. Among the obtained Au catalysts 1/Mn(OH) * 2 and 1/Co(OH) * 2 were most highly active even at 203 K. 1/Fe(OH) * 3 and 1/Ti(OH) * 4 also catalyzed CO oxidation at low temperatures 203-273 K, whereas 1/Fe 2 O 3 and 1/TiO 2 prepared by supporting 1 on conventional Fe 2 O 3 and TiO 2 showed negligible activity under the similar reaction conditions. It was estimated by TEM and XRD that the mean diameter of Au particles in 1/Fe(OH) * 3 was about 2.9 nm, which was about 10 times smaller than that for 1/Fe 2 O 3 . EXAFS for 1/Ti(OH) * 4 revealed that the coordination number of Au-Au bond was 8-10, while that for 1/TiO 2 was 11.0, which also indicates that Au particle size for 1/Ti(OH) * 4 is smaller than that for 1/TiO 2 . The catalysts obtained by attaching the Au complexes on commercially available metal hydroxides also showed negligible activity for the low-temperature CO oxidation under identical conditions. These results demonstrate that supported Au catalysts with small Au particles, tremendously active for the low-temperature CO oxidation, can be prepared by attaching the Au phosphine complexes on the as-precipitated metal hydroxides. Sodium cations exhibited positive effect on the Au catalysis, whereas chloride anions drastically decreased the CO oxidation activity.