Redox cycle during catalysis

Oxides of transition metals, mainly Cr, Mn, Co, Ni, Fe, Cu, and V are employed in the oxidation of organic compounds. Deep oxidation reactions over these metal oxides are considered to be catalyzed by lattice oxygen. A common feature of these metal oxides is the presence of multiple oxidation states. During catalysis, the metal may be reduced by the hydrocarbon and reoxidized by oxygen. It may cycle between two or more oxidation states thus operating in a redox cycle (Mars-van Krevelen mechanism) [12]. However, the actual mechanism of a working catalyst may involve many steps in a number of consecutive or parallel reactions. Because of its low volatility and low toxicity, MnOjc has received the attention of many researchers. 

Human SODl is a dimer of identical subunits, each of which has an essential copper atom in its active site and a zinc atom which is bridged to die copper via Ustidine-63 (Figure 2). The copper atom cycles between Cu(II) and Cu(I) during catalysis while die zinc is redox inactive and drought to play mainly a stmctural role. 

---