Catalytic Hydrodehalogenation of Haloacetic Acids: A Kinetic Study
2020
Nieto-Sandoval, Julia | Gomez-Herrero, Esther | El Morabet, Ferdaus | Munoz, Macarena | de Pedro, Zahara M. | Casas, Jose A.
Haloacetic acids (HAAs) are undesired halogenated byproducts commonly generated upon oxidation treatments carried out in drinking water treatment plants. In this work, the removal of a representative group of these hazardous species (monochloroacetic acid, dichloroacetic acid, trichloroacetic acid, monobromoacetic acid, dibromoacetic acid, and bromochloroacetic acid) by catalytic hydrodehalogenation (HDH) was investigated and kinetic models were accordingly developed. Complete dehalogenation of all these pollutants (0.05 mmol L–¹) was achieved using a Pd/Al₂O₃ catalyst (0.5 g L–¹), although it was found that their reactivity depended on the nature and number of halogen substituents present in the HAA molecule. In general, bromoacetic acids showed higher reactivity than the chlorinated ones, which was attributed to the lower C-X bond dissociation energy. On the other hand, while the chloroacetic acid reactivity increased with the chlorination degree of the molecule, particularly from one to two Cl substituents, the bromoacetic acids did not show higher reaction rates with the increase in Br substituents. Based on the results obtained, different reaction pathways, via stepwise and/or concerted reactions, were proposed for the HDH of the HAAs. Consistent with those pathways, kinetic models were also developed, which allowed describing successfully the experimental data.
显示更多 [+] 显示较少 [-]