Commercial gold supported catalysts

This method is convenient and is used for producing commercial gold sup>-ported catalysts [7, 28]. It is also the one that can be applied to the widest range of different support materials [32]. 

During use, the commercial carbon-supported mercuric chloride deactivates primarily as the result of loss of mercury from the reactor [250]. This is not the case for gold catalysts since, under the reaction conditions used, no gold is lost from the catalyst. In this case, deactivation, as a result of the reduction of Au +, is readily overcome by co-feeding NO. Hence, supported gold nanocatalysts should be the catalysts of choice for this reaction. 

Gold catalysts supported on activated carbon were found to be about three times more active than commercial mercuric chloride catalysts for vinyl chloride production and to deactivate much less rapidly than other supported metal catalysts. Deactivation can be minimised if high loadings of gold are used [18,248,249], Also, Au catalysts can be reactivated by treatment offline with HCl or CD, and by co-feeding NO with the reactants from the start of the reaction, deactivation could be virtually eliminated [259]. Gold is thus the catalyst of choice for this reaction [6,7,18,213,248,249,258,259],... 

When media other than water are used, related processes operate. Thus in acetic acid ethylene gives vinyl acetate, whereas vinyl ethers may be formed in alcohols. Both homogeneous and heterogeneous syntheses of vinyl acetate have been commercialized. The latter process (Hoechst) involves direct oxidation over a palladium-gold catalyst containing alkali acetate on a support ... 

In addition to palladium, the catalysts used commercially always contain alkali salts, preferably potassium acetate. Additional activators include gold, cadmium, platinum, rhodium, barium, while supports such as silica, alumina, aluminosilicates or carbon are used. The catalysts remain in operation for several years but undergo deactivation. The drop in activity is due to a gradual sintering of the palladium particles which causes the catalytically active area to decrease progressively. Under reaction conditions potassium acetate is slowly lost from the catalyst and must continuously be replaced. 

Literature on the use of promoters is voluminous, and all claim enhancement of semi-hydrogenation selectivity. One of the more successful commercial catalysts for ethyne conversion to ethene, uses a silver promoted alumina-supported palladium catalyst [23]. Other promoting metals have been used, including rhodium and gold [24,25], copper [26-28], zinc (shown to inhibit oligomerization) [29-... 

High activity carbide and supported gold water gas shift (WGS) catalysts have been demonstrated. Some of the materials possess rates that exceed those for Cu-Zn-Al commercial catalysts. 

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