Other Types of Supported Catalysts

6 Other Type of Supported Catalysts. - 2.6.1 Ag - Ag Ensembles on Different Supports. Besides copper-containing catalysts both silver and gold can 

Pestryakov and Davydov reported that silver ions are the most active silver species on the surface of different supports (pumice, aluminosilicate, a-AbOs, MgO) in the oxidation of methanol to formaldehyde. 

Silver-containing ceramic catalyst prepared by impregnating acid washed kaolin with silver nitrate solution after calcination in air at 1200 °C appeared to be highly active in the oxidation of methanol to formaldehyde. In this catalyst the silver was stabilized by the presence of [AIO4] in ionic form. Under the reaction conditions, the silver ions were partially reduced by the atomic hydrogen released from methanol and formed metallic particles. XPS and UV-Visible diffuse reflectance spectra (UV-Vis DRS) revealed that after the reaction about one-third of silver in the catalyst was still in ionic state. 

Computational results showed that if silver was positively charged, Lewis acid-base interaction between methanol and silver would be strengthened, and methanol can undergo a stable chemisorbed form on silver surface, which is the key step in the oxidation of methanol to formaldehyde. Also, the further oxidation of formaldehyde was inhibited and the selectivity of the partial oxidation of methanol to formaldehyde was thus enhanced over the positively charged silver catalyst.  

It is noteworthy that electropositive promoters, e.g. iron and zinc, exhibit significant effects modifying both the activity and the selectivity of ethanol formation in the hydrogenolysis of ethyl acetate on supported Group VIII metal catalysts, such as Pd-Zn/AbOs and Co-Rh-Fe/Ti02.  

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