Gold dispersion

However, in some cases oxidic gold species may be the active sites for CO oxidation. Gates reported that oxidic gold dispersed on La203 by using GG of Au acac complex is active at room temperature [43]. On the other hand, we have recently found that over Au/La coprecipitates calcined at temperatures below 500 K are active even at 193 K [46]. The EXAFS and XANES analyses of the active samples showed that oxidic gold stabilized by La(OH)3 is responsible for low-temperature activity. 

In the case of glucose-protected particles, a less important influence of the pH has been observed using more than 7 g/L of glucose. As shown in Table 5, the resultant gold dispersion showed a slow but constant increment of the particle size on standing (ca. 10-20% in 3h). 

In some cases the soluble material is distributed in small isolated pockets in a material which is impermeable to the solvent such as gold dispersed in rock, for example. In such cases the material is crushed so that all the soluble material is exposed to the solvent. If the solid has a cellular structure, the extraction rate will generally be comparatively low because the cell walls provide an additional resistance. In the extraction of sugar from beet, the cell walls perform the important function of impeding the extraction of undesirable constituents of relatively high molecular weight, and the beet should therefore be prepared in long strips so that a relatively small proportion of the cells is ruptured. In the extraction of oil from seeds, the solute is itself liquid. 

T. A. Nijhuis, B. J. Huizinga, M. Makkee, and J. A. Moulijn, Direct epoxidation of propene using gold dispersed on TS-1 and other titanium-containing supports, Ind. Eng. Chem. Res. 38, 884—891... 

Gold dispersion under pediplanation in desert terrains Bimin Zhang Xueqiu Wang , Qinghua Chi Qingtian Lii ... 

Frens, G. (1973) Preparation of gold dispersions of varying size controlled nucle-ation for the regulation of the particle size in monodisperse gold suspensions. Nature Phys. Sci. 241, 20-22. 

Modifying activated carbon fibres (ACF) by ferric oxide improved the gold dispersion and their activity at room temperature, but they deactivated quickly.111... 

As the gold dispersion decreases, the activity drops until it... 

Figure 2. Arrhenius plots for the heterogeneous exchange of isotopic oxygen on NgO and Au/MgO catalysts of varying gold dispersion. See Table I for catalyst code numbers.

A. G. Shastri, A. K. Datye, J. Schwank, Gold-titania interactions Temperature-dependence of surface-area and crystallinity of TiQz and gold dispersion, /. Catal. 87(1) (1984) 265. 

The dependence of activity on the preparation methods observed for Au/C catalysts is presently under investigation. According to the literature data, larger gold particles (10 nm) can be expected with the adsorption method while the other two methods result in smaller particles (2-5 nm) [13]. Thus, a linear correlation between gold dispersion and activity seems to be ruled out. 

A colloidal gold dispersion is prepared as described in Subheading 3.1. 

All glassware used in the preparation of the colloidal gold dispersions must be carefully cleaned in a bath of a freshly prepared 3 1 HNOs + HC1 solution, and then thoroughly rinsed with Milli-Q water, previously filtered through a 22-pm micro-porous Nylon membrane filter (Scharlab), and dried in air. 

Table 13.12 Aerobic oxidation of aromatic aldehydes with gold dispersed on carbon. [Substrate] =0.4M, substrate/metal = 1000, p02 = 3bar, t=2h.

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