CeO2-modified monolithic ceramic foams for efficient catalytic ozonation of refractory organic pollutants in a continuous-flow reactor†

Abstract

Heterogeneous catalytic ozonation is valid for the advanced oxidation of organic pollutants in wastewater, but it is usually used in the packing bed with granular supports/catalysts with considerable fluid resistance and unsatisfactory ozone utilization efficiency in practical wastewater treatment. Herein, CeO₂-modified monolithic ceramic foams (CeO₂/AlCF) were developed for the efficient catalytic ozonation of refractory organic pollutants in a continuous-flow mode. The TOC removal efficiency of phenol by CeO₂/AlCF was about 80% with a hydraulic retention time (HRT) of 12 min. The system also showed high TOC removal efficiencies (68%–81%) for other organic pollutants including oxalic acid, 2,4-dimethylphenol, and p-nitrophenol. The chemical oxygen demand (COD) of the biological treatment effluent of petrochemical wastewater decreased from 136 mg L⁻¹ to 45.2 mg L⁻¹ with a COD removal efficiency of nearly 67%. The ozone utilization efficiencies of CeO₂/AlCF ranged from 53% to 73%, which were much higher than those of granular catalysts (42–68%). The quenching experiments and EPR analysis revealed that the process followed a hydroxyl radical mechanism. H₂ temperature-programmed reduction (H₂-TPR) analysis showed that the transition of Ce⁴⁺ to Ce³⁺ in CeO₂/AlCF was much easier than that in CeO₂ and hence had a better catalytic capability.