Redox chemistry oxidation state rules

Complexing can have a strong effect on redox chemistry, the general rule being that a ligand stabilises whichever oxidation state it complexes with most strongly. Two important examples are —... 

Unlike sulfur, phosphorus compounds are not believed to directly poison the noble metals. This may owe to the extreme difficulty of reducing phosphorus below the +3 state. Also unlike sulfur, cerium phosphate chemistry does not have a corresponding redox chemistry that can provide a secondary source of OSC. Cerium phosphates, once formed (likely from P2O5 or H3PO4 precursors), trap the ceria in the 3+ oxidation state and irreversibly poison OSC. Moreover, one cannot rule out the possibility that this may be facilitated by the noble metals thus leading to preferential poisoning of ceria in the vicinity of the noble metal particles. 

Our radiolysis studies also indicate that phosphonates react quite slowly with the superoxide anion radical. Although our studies do not support the formation of radical cations as an initial oxidation step, we cannot rule out the possibility that radical cations are not involved in the oxidation of the C—P bond, as previously proposed [44], It is also possible that more electron-rich organphosphorus compounds or organophosphorus compounds in the adsorbed state may exhibit different redox and hydroxyl radical chemistries than what is observed under pulse radiolysis employing homogeneous conditions. 

---