Innovative iron oxide foams for the removal of micropollutants by Catalytic Wet Peroxide Oxidation: Assessment of long-term operation under continuous mode

Abstract

This work aims to develop highly stable iron oxide foams for the continuous Catalytic Wet Peroxide Oxidation (CWPO) of micropollutants in a structured fixed-bed reactor. Homogeneity and adhesion of the active phase were achieved by adjusting the preparation methodology. Three structured catalysts based on Al2O3, SiC and ZrO2 foams were obtained with Fe content of 2.5%, 2.1% and 0.90% wt., respectively. The catalytic foams were tested in the CWPO of a mixture of three pharmaceuticals (metronidazole (MNZ), sulfamethoxazole (SMX) and carbamazepine (CBZ)), with a concentration of 100 µg L−1 each. The catalysts resulted active and stable up to 200 h of CWPO carried out at ambient conditions, with the exception of Fe/ZrO2, which showed a progressive deactivation due to the iron leaching from the solid. An increase in space time led to an enhanced performance achieving remarkable conversion levels of 73%, 83% and 90% for MNZ, SMX and CBZ, respectively. The effect of H2O2 dose was also evaluated revealing the development of competing side reactions for supra-stoichiometric dosages. Moreover, the scavenging effect of the water matrix was assessed operating in presence of humic acid as representative natural organic matter (NOM). In this case, the conversion levels for SMX and CBZ resulted alike to the ones obtained for ultrapure water and only a slight decrease in MNZ removal rate was detected. After 400 h of usage at different steady-state conditions, the outstanding catalytic performance of Fe/Al2O3 and Fe/SiC was sustained in the long-term operation.