Mechanism of Ethylene Oxychlorination on Ceria

This is the authors' abstract. We don't add key points for this paper.

Ethylene oxychlorination on CeO 2 provides ethylene dichloride (EDC) and the desired vinyl chloride (VCM) in a single operation, in contrast to the traditional process that requires two separate units. The origin of this outstanding performance is unclear, and the mechanism has not been discussed in detail. In the present work, we combine density functional theory (DFT) with steady-state experiments and temporal analysis of products (TAP) to close this gap. The catalyst surface is found to contain CeOCl, while the bulk phase is CeO 2, regardless of the starting materials CeCl 3, CeOCl, or CeO 2 . Catalysis by different nanostructures highlights that the CeO 2 (111) surface is more active than the (100) surface due to the poisoning of the latter, while the selectivities are comparable. In any case, the degree of oxygen removal from CeO 2 and the replenishment of the accordingly formed oxygen vacancies by Cl and its replenishment by Cl species lead to increased selectivity to chlorinated products and decreased selectivity to carbon oxides. DFT and TAP studies reveal that the most likely pathway of VCM formation takes place by a cascade reaction. First, EDC appears and then HCl is extracted in a concerted step to lead to VCM. Such steps are a key characteristic of ceria. Other paths leading to minor products such as 1,2-dichloroethene (DCE) are found possible by starting from VCM or EDC. CO is formed by combustion of chlorinated species, whereas CO 2 can either stem from further oxidation of CO or directly from ethylene. In summary, our work points out a rich complex behavior of the chemistry of chlorinated compounds on the oxide surface, indicating that concerted steps and cascade reactions are possible for these materials.