Identification of by-products and toxicity assessment in aqueous-phase hydrodechlorination of diuron with palladium on activated carbon catalysts

• The GS-Pd catalyst achieved the complete diuron conversion above 50 °C.
• A complete route of hydrogenation of diuron was elucidated.
• The most favorable route is the proceeding towards fenuron and monuron.
• The HDC effluents showed lower ecotoxicity values than the starting diuron solution.

The hydrodechlorination (HDC) of diuron in aqueous phase with hydrogen using two different activated carbon-supported Pd catalysts was studied. A commercial activated carbon and one prepared by chemical activation of grape seeds with phosphoric acid (GS) were evaluated as supports, being the catalysts tested in a wide range of temperature (30–100 °C) and space–time (78–311 kgcat h mol−1). Diuron conversion was above 70% under all the conditions tested. The Pd catalyst supported on GS showed the highest activity in terms of diuron conversion within the temperature range studied, allowing nearly complete conversion above 50 °C. However, a gradual loss of activity with time was observed for this catalyst. A complete route of hydrogenation of diuron was elucidated. Two reaction routes one leading to fenuron and another to aniline were identified. As the temperature and space–time were increased, the formation of fenuron (via monuron) was found to be favored. The toxicity of the reaction products was evaluated, being the route to fenuron and monuron, the one giving rise to a significant decrease of ecotoxicity.