Reductive dissolution and oxidative catalysis of an immobilized iron oxide in the presence of catechol and phenol

Abstract

An original study of an immobilized iron oxide catalyst (SiG1) with one hydroxylation intermediate of phenol (catechol) in the reductive dissolution process was performed. Also, SiG1 was applied as the catalyst for the oxidation of phenol and catechol in the presence of hydrogen peroxide. The SiG1 used in this study reacted more efficiently with catechol than the other iron oxides. Only the hydroxylation intermediates of phenol (i.e. catechol and 1,4-hydroquinone) were able to reductively dissolve SiG1. However, there are no interactions between SiG1 and phenol. The reductive dissolution of SiG1 not only occurred at acidic solution but also occurred at alkali solution in the presence of catechol. Furthermore, the solution of pH 5 was found to be a critical condition in which the interactions of SiG1 and catechol were weak in the presence or absence of H 2O 2. The yields of Fe 2+ from SiG1 in the presence of catechol were limited by the equilibrium of reduction and the oxidation rate of iron(III, II) species. A kinetic model was applied to obtain the estimated maximum concentration of Fe 2+ produced by SiG1 and estimated proportional constant in the presence of catechol at different pH conditions by using a trial and error method. Catechol induced the reductive dissolution of SiG1 and then promoted its own oxidation along with that of phenol in the presence of hydrogen peroxide.