Catalytic hydrodechlorination and advanced oxidation processes of 2,4-dichlorophenoxyacetic acid over CMK-3 supported catalyst: The bi-functional effect of metal Pd

The Pd/CMK-3 catalyst reflected a good advanced oxidation ability based on PMS activation in situ after the highly effective catalytic hydrodechlorination of 2,4-D. • The HDC, AOPs and combined HDC-AOPs of 2,4-D were conducted over Pd/CMK-3. • Active Pd species exhibited distinct effects in the HDC and AOPs. • HDC product could be further degraded in the presence of PMS in situ. • Surface-bound free radicals contributed most to the AOPs of 2,4-D. • Metal Pd was more stable after HDC than that of AOPs. The eliminate of 2,4-dichlorophenoxyacetic acid (2,4-D) was achieved via individual and combination of catalytic hydrodechlorination (HDC) and AOPs involved peroxymonosulfate activation. The CMK-3 supported monometallic Pd catalysts with varied Pd loadings were prepared and applied in the reactions. The results showed that Pd/CMK-3 were highly active and competitive in both the HDC and AOPs of 2,4-D, and the removal efficiencies were 91.6 and 95.2% over Pd 3 /CMK-3 respectively after reaction for 90 min. The dechlorination of 2,4-D was completed via both the stepwise and concerted pathways while the reactant experienced free radical oxidation processes in the AOPs. For the combined HDC-AOPs reaction, Pd/CMK-3 reflected a good advanced oxidation ability after the effective HDC of 2,4-D. Additionally, the catalysts exhibited higher Pd n+ /Pd 0 ratios after reactions and metal Pd was more stable after the reductive dechlorination than that of advanced oxidation.