Gold particles supports

Figure 30. Conversion of glucose as a function of reciprocal diameter of gold particles supported on activated carbon.

Five different preparations, from the sol production to the adsorption step, were carried out to verify the reproducibility of the dimension of the gold particles supported on XC72R carbon. In Table 9 the results are collected, indicating a fairly good confidence with the experiments reported in the above sections. 

In addition to titania, alumina and ceria supports (Table 4.4), the DPU method has been applied to other supports. Gold particles supported on ferric oxide were quite small (3-7 nm) after thermal treatment is static air at 623 K.80 Another study reported the use of the DPU method to deposit gold onto other supports (MgO, CaO, SrC>2 and BaO).81 After calcination at 673 K, gold particles of moderate size were obtained on magnesia (8 nm) and on calcia (6nm). In all cases, all the gold in solution was deposited on the support. 

We have recently conducted a series of mass-selected experiments, employing the GIB-MS technique on the reactivity of aluminum oxide ions with CO. These experiments were motivated by a recent condensed-phase study where gold particles supported on alumina were found to be highly active in the oxidation of CO [85]. Alumina is an ideal catalyst support material due to its high mechanical... 

Figure 7 TEM picture (362 x 270 nm ) of gold particles supported on mica. (From S. Ferrero, A. Piednoir, and C.R. Henry [133].)...

Primary alcohols are converted into silyl ethers by RsSiH using nanosized gold particles supported on alumina. Under the same conditions aromatic aldehydes are coupled and silylated. 

Infiared spectra of CO adsorbed on nanometric gold particles supported on different supports, both oxidised and reduced, are reported. Depending on the nature of the supports, on the pretreatments and on the size of the gold nanopaiticles, different gold carbonylic species have been evidenced. The electronic and structural properties of gold nanoparticles and the electron-donating effects of reducible supports are shown to be relevant in determining the chemisorption and catalytic properties of the samples. 

Molecular beam experiments performed with -1.5 nm gold particles supported on an MgO(lOO) surface annealed in UHV at 973 K [171] showed that, after exposure to an O2 beam then pumping, no CO2 was produced during CO pulse titration, indicating that O2 does not dissociate on gold before reaction with adsorbed CO. The authors are more in favor of a mechanism at the interface, as proposed... 

Gold particles supported on titania are active catalysts for the low temperature oxidation of CO. This phenomenon was originally discovered by Haruta and coworkers in the early 1990s, and has been corroborated by many subsequent studies. - - - - The exact catalytic activity of the Au/TiOj system depends on the method of preparation and the dispersion of the metal on the support, but in general Au particles with sizes between 2 and 4 nm display a catalytic activity for CO oxidation much larger than that of bulk metallic gold. New preparation methods aim for the synthesis of very small Au particles (< 2 nm) with an extremely high catalytic activity. ... 

Fig. 16.12 SECM TG-SC images displaying the substrate curroit for ORR of an array composed by 3 different types of shape-controlled gold particles supported rai a glassy carbon plate. Substrate potential held constant at (a) 0.35 V, (b) 0.45 V, and (c) 0.55 V vctsus RHE in an oxygen-free 0.1 M NaOH solution. Tip-substrate distance = 25 pm. Oxygen flux generated at the tip at a constant current of 150 nA. Scan rate = 125 pm s (extracted from [70])...

The support can participate at the interface. The interface sites can have chemical properties that are different from those of both phases. This may be one of the reasons gold particles supported on TiO have catalytic properties different from those of bulk (unsupported) gold. 

It was concluded that gold particle-support interaction is required together with careful selection of the titania-silica support and control of the gold-particle size. The use of pH 7.0 in the deposition-precipitation method was also recommended, together with calcination at 573 K. Propene oxide has recently been obtained via a two-stage process involving dehydrogenation of propane to propene (selectivity of 57%), followed by a propene to propene oxide oxidation with a selectivity of 8%, and... 

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