Wet-Oxidation Catalysts

Department of Chemistry, Kyoto Institute of Technology Matsugasaki, Sakyo-ku, Kyoto 606-8585, Japan 

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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. 

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