Effect of TiO2 on Ru/ZrO2 catalysts in the catalytic wet air oxidation of isothiazolone

Abstract

For the first time, Ru/xTiZrO₄ catalysts were evaluated in the catalytic wet air oxidation (CWAO) reaction of isothiazolone. The structures of the Ru/xTiZrO₄ catalysts were examined using Brunauer–Emmett–Teller (BET) measurements, X-ray diffraction, temperature programmed reduction, CO chemisorption, mechanical strength analysis, scanning electron microscopy, energy dispersive X-ray spectroscopy, zeta-potential measurement and thermogravimetric analysis. The effect of TiO₂ content on the activity for TOC removal and mechanical and chemical stability of the Ru/xTiZrO₄ catalysts was evaluated. The results indicated that the addition of TiO₂ as a second oxide component hindered the crystallization of pure ZrO₂, improved the crushing strength of the catalyst and increased the bonding strength of RuO_x and the support. For Ru/xTiZrO₄ catalysts (x < 0.2), the addition of TiO₂ enhanced the activity for TOC removal. For x > 0.2, the addition of TiO₂ reduced the activity for TOC removal; however, the mechanical stability of the catalysts was enhanced. The Ru/0.2TiZrO₄ catalyst exhibited high activity for TOC removal and good mechanical stability and was therefore selected as the optimal catalyst to treat isothiazolone wastewater using CWAO. For the reaction temperature of 200 °C and LHSV of 2 h⁻¹, the isothiazolone conversion, TOC and TN removal reached 100%, 82.6% and 44.5%, respectively. Finally, the degradation pathway of isothiazolone in CWAO was proposed. Throughout the 240 h evaluation period, the isothiazolone conversion and total organic carbon removal remained at values greater than 99% and 82%, respectively, indicating that the Ru/0.2TiZrO₄ catalyst exhibited good chemical stability.