Kinetic Study of the Oxidation of Hydrogen Sulfide by Fe (III)-Tetrapolyphosphate (TPP) and Fe (II)-TPP by O2

Safarzadeh-Amiri, A., Zhang, Y., & El-Din, M. G.

Applied Catalysis B: Environmental 218 (2017): 186-191.

Tetrapolyphosphate (TPP) forms complex with iron(III) (Fe(III)-TTP), which is a highly stable catalyst for the air/O2 oxidation of HS in both the buffered and non-buffered solutions. The first step in this process is formation of the Fe(III)(HS)TPP complex followed by an electrontransfer from HS to Fe(III) and formation of Fe(II)TPP and HS•. The electron transfer process depends on the half-wave potential (E1/2) of the complex. The E1/2 of Fe(III)/(II)TPP was measured electrochemically and it was found to decrease from 0.061 to −0.14 V vs. SHE (standard hydrogen electrode) with increasing solution pH from 4 to 9. The oxidation of Fe(II)TPP by O2 is shown to follow a four-step reaction mechanism, and the reaction kinetic parameters were calculated using experimental data. The second-order rate constant of the reaction between Fe(III)TPP and HS at pH 9 was found−within 95% confidence limit-to be about 30.5 ± 21.0 M−1s−1. This study provided valuable information about the oxidation characteristics of Fe(II)TPP by O2 and the capability of Fe(III)TPP as a catalyst for the air/O2 oxidation of HS.


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