Effect of Ru on the activity of Co3O4 catalysts for chlorinated aromatics oxidation

Abstract

Ru/Co₃O₄ catalysts with a Ru content of 0–2 wt% were prepared by wet impregnation, and used in the catalytic combustion of chlorinated aromatic VOCs. Characterization by XRD, HRTEM, EXAFS, XPS, and H₂-TPR showed that Co₃O₄ existed in the form of a spinel structure. Some Ru species entered the octahedral sites of Co₃O₄ to form Ru–O–Co, which significantly increased the surface oxygen, while the formation of RuO_x clusters or nanoparticles on the surface promoted the reducibility of Co₃O₄. In the oxidation of chlorinated aromatics, Ru species can retard the negative effect of Cl species on the activity of Co₃O₄ catalysts through modification in the chemical environments of surface oxygen and Cl species. The Ru/Co₃O₄ catalysts presented good activity and selectivity, with a rate (R_Ru) of 9.4–9.8 μmol m⁻² min⁻¹ under 1000 ppm 1,2-dichlorobenzene at 30 000 ml g⁻¹ h⁻¹. The R_Ru in wet feed over 2.0% Ru/Co₃O₄ was increased by almost 100%, through the increase in availability of active surface oxygen from RuO_x. A highly stable activity could be maintained for at least 50 h. In situ FT-IR showed that 1,2-DCB adsorbs on the Co³⁺/Co²⁺ sites of Ru/Co₃O₄ catalysts, and the formation of partial oxidation products involve the surface oxygen. For the Co₃O₄ catalyst, surface active oxygen is almost not available during 1,2-DCB oxidation.