Gold catalysts, supported

M. Haruta, A. Ueda, S. Tsubota, and R.M.T. Sanchez, Low-temperature catalytic combustion of methanol and its decomposed derivative over supported gold catalysts, Catalysis Today 29, 443-447 (1996). 

Homogeneous deposition of ultrafine metal particles on the surfaces of fine powder is not easy using PVD. A device for stirring the powder support in a vacuum chamber is needed to avoid heterogeneous deposition. Sputter deposition units equipped with stirring powder supports have already been adapted for the industrial production of Ti02 and carbon-supported gold catalysts by 3M [35]. 

Supported gold catalysts are, in general, less active than platinum group metal catalysts in the complete oxidation of hydrocarbons however, by choosing... 

CO conversions over Au/Ce02 catalyst were measured in the dry and wet condition as shown in Fig. 1. Similar to other supported gold catalysts, Au/Ce02 catalyst showed higher CO conversions in the presence of water vapor than in the absence of it at the same temperature. Catalytic activities for CO oxidation over Au/Ce02 catalysts prepared at different calcinations temperature were compared in the dry and wet condition as shown in Fig. 2. Au/Ce02 catalyst calcined at 473 K showed the highest initial CO conversion in the absence of water vapor. However, the CO conversion decreased steadily and reached a steady-state value over this catalyst. 

Titanium dioxide supported gold catalysts exhibit excellent activity for CO oxidation even at temperatures as low as 90 K [1]. The key is the high dispersion of the nanostructured gold particles over the semiconducting Ti02 support. The potential applications of ambient temperature CO oxidation catalysts include air purifier, gas sensor and fuel cell [2]. This work investigates the effects of ozone pretreatment on the performance of Au/Ti02 for CO oxidation. 

The intense recent interest in supported gold catalysts has focused on small, nonuniform clusters (e.g., those supported on Ti02), which have been... 

Figure 1. TEM image of a titania supported gold catalyst (1.7wt.% Au) prepared by deposition-precipitation (gold particle size = 5.3+ 0.3 nm, dispersion = 36%). (Reprinted from Reference [84], 2000, with permission from American Chemical Society).

Since Haruta s works in the 1980s [110] CO oxidation is one of the major applications of supported gold catalysts. Interestingly, this metal/substrate combination exhibits much more pronounced structure sensitivity than the Pd, Pt, and Ir catalyzed analogues [9]. 

Figure 9. CO conversion as a function of temperature for supported gold catalysts (a) Au/Zr02, (b) Au/Ti02 (both PVA protected) (Reprinted from Reference [24], 2006, with permission from American Chemical Society).

Size Control of Metal Nanoclusters in Supported Gold Catalysts... 

Figure 14. Reaction pathways for CO oxidation over supported gold catalysts [39].

B. Nkosi, N. J. Coville, G. J. Hutchings, M. D. Adams, J. Friedl, and F. Wagner, Hydrochlorination of acetylene using carbon-supported gold catalysts A study of catalyst reactivation, J. Catal. 128(2), 378-386(1991). 

B. Qiao, and Y. Deng, Highly effective ferric hydroxide supported gold catalyst for selective oxidation of CO in the presence of H2, Chem. Commun. 17, 2192-2193 (2003). 

Curves (a) and (b) in Fig. 5.3 compare the light-off curves for the gold catalysts supported on anatase and brookite after being treated with O2 at 300°C. Interestingly, the catalytic activity of the brookite-supported gold catalyst remained highly active, with the onset for 100% CO conversion occurring around —20°C. In contrast, the onset... 

J. D. Grunwaldt, C. Kiener, C. Wogerbauer, and A. Baiker, Preparation of supported gold catalysts for low-temperature CO oxidation via size-controlled gold colloids, J. Catal. 181(2), 223—232 (1999). 

M. M. Schubert, S. Hackenberg, A. C. van Veen, M. Muhler, V. Plzak, and R. J. Behm, CO oxidation over supported gold catalysts— Inert and active support materials and their role for the oxygen supply during reaction, J. Catal. 197, 113-122 (2001). 

The exceptional renewed interest in supported gold catalysts leads us to mention here a few recent examples of the formation of in situ gold carbonyl species from supported gold that can be related to the preparation of supported Au nanoclusters [53-55]. On the other hand, bimetallic carbonyl cluster salts of [Au4Fe4(CO)i,5] and [AuFe4(CO)i,5] have been used recently in the preparation of Au/Fe0,t/Ti02 catalysts for the total oxidation of dichlorobenzene and toluene [56]. 

Kozlova, A.P. Sugiyama, S. Kozlov, A.I. Asa-kura, K. Iwasawa.Y. (1998) Iron oxide supported gold catalysts derived from gold phosphor complex Au(PPh3) (NO3) State and structure of the support. J. Catalysis 176 426-438... 

Claus recently reviewed the hydrogenation of a,P-unsaturated aldehydes, a process that displays very high selectivity by supported gold catalysts [215]. 

One more step was proposed after it was found that the addition of a second metal to the supported gold catalyst could refine the selectivity of the process. 

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