Efficient Elimination of Chlorinated Organics on a Phosphoric Acid Modified CeO2 Catalyst: A Hydrolytic Destruction Route

• Published in: Environmental science & technology 2019-11, Vol.53 (21), p.12697-12705
• Main Authors: Dai, Xiaoxia, Wang, Xinwei, Long, Yunpeng, Pattisson, Samuel, Lu, Yunhao, Morgan, David J, Taylor, Stuart H, Carter, James H, Hutchings, Graham J, Wu, Zhongbiao, Weng, Xiaole
• Format: Article
• Language: English
• Subjects: Byproducts; Catalysis; Catalysts; Cerium oxides; Chlorination; Chlorobenzene; Congeners; Decomposition reactions; Density functional theory; Destruction; Dioxins; Environmental chemistry; Free energy; Heat of formation; Organic chemistry; Oxidation; Phenols; Phosphates; Phosphoric acid
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/acs.est.9b05088

The development of efficient technologies to prevent the emission of hazardous chlorinated organics from industrial sources without forming harmful byproducts, such as dioxins, is a major challenge in environmental chemistry. Herein, we report a new hydrolytic destruction route for efficient chlorinated organics elimination and demonstrate that phosphoric acid-modified CeO2 (HP-CeO2) can decompose chlorobenzene (CB) without forming polychlorinated congeners under the industry-relevant reaction conditions. The active site and reaction pathway were investigated, and it was found that surface phosphate groups initially react with CB and water to form phenol and HCl, followed by deep oxidation. The high on-stream stability of the catalyst was due to the efficient generation of HCl, which removes Cl from the catalyst surface and ensures O2 activation and therefore deep oxidation of the hydrocarbons. Subsequent density functional theory calculations revealed a distinctly decreased formation energy of an oxygen vacancy at nearest (VO‑1) and next-nearest (VO‑2) surface sites to the bonded phosphate groups, which likely contributes to the high rate of oxidation observed over the catalyst. Significantly, no dioxins, which are frequently formed in the conventional oxidation route, were observed. This work not only reports an efficient route and corresponding phosphate active site for chlorinated organics elimination but also illustrates that the rational design of the reaction route can solve some of the most important challenges in environmental catalysis.