Gold in ordered mesoporous silica

The preparation of gold particles in mesoporous materials covers a wide field, relating not only to catalysis, but also to materials science and domains of physics, including optical and electrical properties. Many methods of preparation have been used, but one wonders why some people have laboured to develop very sophisticated methods while others have been content with a much simpler method, apparently giving the same result, namely, the desired small gold particles. 

Gold has also been introduced into MCM-41 of various pore sizes (2.2-3.1 nm) by CVD with Me2Au(acac) followed by calcination at 673 K 97 particle sizes were 3-4 nm, smaller than on amorphous silica and with a narrower size distribution (Table 4.7). The gold particles, some of which were rod-like, appeared to be well distributed throughout the pore structure, although their sizes were slightly larger than the pore diameters. 

More sophisticated methods involve functionalising the support before exposure to HAuCL solution. This may be achieved by incorporation of a reagent during the synthesis that produces either propylamine, or propy-lthiol groups on the surface of MCM-41145 and SBA-15.146 

Post-synthesis treatment of SBA-15 by silanation with [NIt R3]+Cl-(R/ = silane) gives a cationic function, which has allowed adsorption of Au(OH)nClJ n anions at various values of pH.147,148 These methods give usefully small particle sizes ( 2.5 nm) and sometimes quite high metal loading (16wt.%), but they exhibit poor catalytic properties in oxidation of carbon monoxide148 (Section 6.3.3.4). 

It has to be stressed that the objective of these methods was not always to produce active catalysts, so the fate of the gold particles after 

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