Precious metal / oxide, wetting

The precious metals are generally introduced in the catalyst by wet chemical methods such as incipient wetness impregnation, typically using aqueous solutions of the precious metal salts, followed by a drying step to remove the water, and then by a caleination step to decompose the precious metal salts. Sometimes, a reduction step is applied to convert the precious metal oxides into the metallic state. Other production procedures are used as well and are described in the patent literature. 

Although CeO, is a good support and Ru seems to be the best active component among precious metals, there is work which shows that CeO, and/or Ru is not necessarily the best choice as catalyst components. Dobrynkin et al. carried out the wet-oxidation of N-containing compounds such as acetonitrile, carbamide. 

CeOj is an inevitable component in the automobile exhaust purification catalysts in which precious metals are the main active elements. In the wet-oxidation catalysts based on precious metals, CeO also plays a very important role in activating them. 

Based on the above discussion, the function of the wet-oxidation catalysts should be confined to (i) activation of oxygen and (ii) direct electron transfer with the reactants (redox reaction) in the first step of the reaction. CeO seems to effectively contribute to both factors. CeOj behaves quite differently from other oxides of lanthanide and is always a constituent of automobile-exhaust purification catalysts. It stabilizes supports and keeps high surface area [64,65], prevents the sintering of precious metals and, thus, stabilizes their dispersed state [66,67], and acts as an oxygen reservoir [68,72]. When combined with precious metals, it works in various reactions other than the purification of vehicle exhausts e.g., detoxification of NjO, methanol decomposition, methanol synthesis, combustion of formaldehyde, etc [47,73-75]. Precious metals are remarkably activated and behave quite differently on CeO compared with their action on other supports. 

Precious metals (Pt, Pd, Ru) deposited on supports have been reported to be active for catalytic wet air oxidation (CWAO). Gallezot et al [9] have shown that platinum catalysts supported on carbon could decompose formic, oxalic and maleic acids very easily, at... 

Chlorination technique has been developed to make the precious metals water soluble that is, effective for a low concentration sample, alloy, or sulfide mineral. Chlorination consists of both dry and wet methods. Chlorination gives a low reagent blank, and is used in combination with high-sensitivity detection. In the wet chlorination method, the samples are pressurized in a closed vessel with an oxidizing agent and hydrochloric acid, and dissolved... 

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