Catalytic oxidation of vinyl chloride over zirconium-modified Co3O4 catalysts
Résumé
Volatile organic compounds (VOCs), released from a wide range of industrial processes, are considered as heavy environment pollutions due to their high toxicity and degradation-resistant. More specifically, chlorinated VOCs (CVOCs) are a typical class of VOCs, containing one or several chlorine atoms, which are difficult to be degraded. In the past decades, more and more attention has been attracted to develop different technologies to convert CVOCs into CO2, H2O, HCl or Cl2. Among them, catalytic oxidation is a promising method, which can occur at a low temperature with high efficiency. Co3O4 has been proved to be an efficient catalyst for CVOCs oxidation and ZrO2 has been widely used in various formulations as a promoter or supporter to improve amphoteric properties and high thermal stability. In this work, A series of ZrO2-Co3O4 catalysts was prepared by a sol-gel method and tested in the catalytic oxidation of 1000 ppm vinyl chloride (VC) balanced by air at a WHSV of 30000 mL g-1 h-1. The catalyst with 5% zirconium (Co95Zr5) presented the best activity, especially for the total oxidation of chlorinated by-products. XRD, Raman, N2 adsorption-desorption, FE-SEM, H2-TPR, NH3-TPD, XPS were used to characterize the physicochemical properties of the samples. It was found that a small amount of zirconium introduced to the Co3O4 catalyst modified the redox ability of the Co3O4 catalyst, enhanced its surface acidity, and finally improved the oxidation of CVOCs. The amounts of surface Co2+ increased with the amount of zirconium as revealed by XPS analysis, indicating the formation of more active oxygen species, thus promoted the conversion of VC and improved the catalytic activity. As the reaction temperature increased, the formation of Cl2 improved slightly due to the Deacon reaction. Furthermore, the best catalyst (Co95Zr5) showed good performance in a long-term stability test.