Effect of Residual Chlorine on the Catalytic Performance of Co3O4 for CO Oxidation

An oxide catalyst plays an important role in environmental catalysis. Metal chlorides are widely used as precursors in the preparation of oxide catalysts. However, residual chlorine usually influences the performance of catalysts. In this work, we systematically investigate the influence and efficient removal of chlorine residue on the Co3O4 catalyst in CO oxidation by control experiments and related characterizations. Compared to the cobalt nitrate-derived catalyst, the cobalt chloride-derived Co3O4 catalyst shows a significant improvement in catalytic activity after being washed with water, suggesting that residual chlorine exerts a detrimental effect on the Co3O4 catalyst in CO oxidation. Further investigations show that residual chlorine inhibits the activity of surface oxygen species as well as blocks the active sites. It is noteworthy that residual chlorine cannot be efficiently removed before the calcination because of the strong interactions between the chloride anions and cobalt precursor. In addition, the washed chloride-derived catalyst even shows a better catalytic performance than the nitrate-derived one because of more active sites that are exposed on the surface with the removal of residual chlorine. More importantly, most of the commercial Co3O4 samples are found to be seriously poisoned by chlorine. Hence, efficient elimination of residual chlorine is very important and should be undertaken before the use of catalysts in the case of using chlorides as precursors.