Effect of vanadium on the catalytic activity of ceria towards wet peroxide oxidation of persistent and biorecalcitrant chlorinated organics

Abstract

Chlorinated aromatic compounds are recalcitrant to biodegradation and conventional treatment methods Herein, we investigate the efficiency of catalysts in the oxidation of 4-chlorophenol (4-CP) and 2,4-dichlorophenoxyacetic acid over CexV1-xO2 (x: 0, 0.25, 0.5, 0.75, 1) nano oxides with hydrogen peroxide in water. The catalysts were characterised by temperature programmed reduction (H2-TPR) and desorption (NH3-TPD and CO2-TPD) techniques. Effect of reaction variables like catalyst dosage, H2O2 and reactant concentrations and temperature, were investigated. The results show that 500mg/L 4-CP is completely removed with 0.13mol/L of H2O2 over 500mg/L Ce0.75V0.25O2, within 135min with the total organic carbon (TOC) removal of 21.56%. Within 75min, 250mg/L 2,4-D is completely degraded by 0.08mol/L H2O2 over 500mg/L Ce0.5V0.5O2 with 30.15% TOC removal. The major degradation intermediates are phenol, benzoquinone and 2,5-hexane dione as identified by gas chromatography mass spectrometry (GC–MS). Based on these, a possible reaction mechanism is proposed. The stability and reusability of the mixed oxides during five consecutive cycles was experimented by X-ray diffraction (XRD) and surface area measurements. The catalytic efficiency is retained after five successive runs and the catalysts are texturally stable Scavenging experiments revealed the activation of reaction through the formation of hydroxyl radicals.