Gold catalysts preparation methods

Glaner, L. and van der Lingen, E. and Cortie, M. B. (2003) Gold catalysts and methods for their preparation, Australian Patent 2003/215039. 

In addition, the catalyst preparation method plays an important role sol immobilization appears superior to incipient wetness or impregnation methods. Gold sol immobilization occurs via citrate reduction of HAuCU, yielding a narrow par-... 

Table 10.1 Activities of supported gold catalysts prepared by different methods (3% Au) for the water-gas shift temperatures for 50%...

Since supported gold catalysts prepared by coprecipitation were found to be active for CO oxidation even at temperatures far below room temperature, attempts are increasing to prepare other noble metal catalysts by coprecipitation, deposition-precipitation, and grafting methods, which were used for the preparation of active supported gold catalysts. Although the affinity to CO is markedly different between Pt-group metals and Au supported on selected metal oxides, the contribution of metal-support interactions to the enhancement of low-temperature catalytic activity for CO oxidation appears to be similar, namely, the enhancement of oxygen activation at the perimeter interface. This line of approach may be valid to seek for a new type of catalysts active at lower temperatures for reactions other than CO oxidation [82,83]. 

Prom the numerous results published on catalytic gold, it is clear that for particles larger than about 5nm the activity is very low. Haruta and co-workers [73] showed that for the CO oxidation at RT on gold catalysts prepared by chemical methods, the activity is maximum for sizes of around 3nm (see Fig. 3.16). This result was later confirmed by Goodman and coworkers [74] on Au particles grown by vacuum evaporation on TiO2(110). 

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. ... 

As already mentioned, there a few important factors for achieving good performance of WGS gold-ceria catalysts preparation method, the dispersion of the gold, and the state and nature of the supports. The latter is of crucial importance for the preparation of not only active but also very stable catalysts for WGS reactions. For this reason ceria is a very good choice. 

The present studies exhibited the prospects of the method of deposition-precipitation with ammonia for the gold catalyst preparation using [Au(NH3)4] synthesiz from HAuCk solution. As compared with the previously published DP ns procedures, the proposed procedure makes possible almost complete deposition (>99%) of gold from HAuCk solution on the Si02 and Ti02 supports at the low ratio NH3 Au = 6.5-7 and pH<6. The highly dispersed gold particles are catalytically active in the liquid phase oxidation of piperonyl alcohol to aldehyde and in the S-VOC removal. 

This method is one of the dry methods in which no chemical reaction is involved. Preparation of ultrafine particles by physical vapor deposition (PVD) dose not require washing and calcination, which are indispensable for chemical preparation such as in CP and DP methods. As waste water and waste gases are not by-produced, the arc plasma (AP) method is expected to grow in popularity as one of the industrial production methods for gold catalysts and as a clean preparation method. 

Highly active gold catalysts can be prepared by an appropriate selection of preparation methods such as CP, DP, DR, and SG with dimethyl Au(III) acetylacetonate, depending on the kind of support materials and reactions... 

The activity of gold catalyst is normally strongly size dependent and the control as well as the narrowest possible distribution of particle size represent the main goal for the production of an active gold catalyst. From a catalytic point of view, several preparation methods have been proposed for obtaining highly dispersed gold catalyst, most of them derived from deposition-precipitation method proposed by Haruta et al. [3]. 

The activity of a gold catalyst depends largely on the conditions used for calcination or on the preparation method. 

The very first supported gold catalysts were prepared by impregnation (IMP)9,41 since this is the simplest method, and can be used with any support. The precursors most often used were chloroauric acid... 

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