Ultra-fast catalytic hydrodechlorination of chloroacetic acids over Pd catalyst supported on CeO2 with exposed (110) plane

Chloroacetic acids were frequently detected in the chlorination drinking water. Herein, Pd/CeO2 catalysts with varied CeO2 exposed planes were prepared, and the catalysts were applied for the liquid phase hydro-dechlorination (HDC) of monochloroacetic acid (MCAA) at ambient temperature and pressure. The CeO2 nanorod (r-CeO2) with (1 1 0) plane supported Pd catalysts showed higher Pd dispersion and CO adsorption amount than that of CeO2 nanocube (c-CeO2) with (1 0 0) face and octahedron counterparts (o-CeO2) with (1 1 1) plane. The HDC rate of MCAA reached 99.5% after reaction for 5 min at a catalyst dosage of 0.1 g l- 1 under pH 5.6 over the dp-Pd1/r-CeO2 catalyst prepared via the deposition precipitation (dp) method. The MCAA removal efficiencies were only 19.8% and 11.5% over dp-Pd1/c-CeO2 and dp-Pd1/o-CeO2, respectively. DFT simulation results showed that the adsorption energy between Pd and r-CeO2 was higher than that of CeO2 nanocube and octahedron, suggesting that compared with (1 0 0) and (1 1 1) planes, the r-CeO2 with exposed (1 1 0) plane favored the anchor of Pd nanoparticles. Higher Pd dispersion and appropriate Pdn+/Pd0 ratio (0.86) accounted for the ultra-fast catalytic HDC reaction. Additionally, the pre-adsorption of reactant over the catalyst surface favored the HDC reaction. The HDC of polychlorinated acetic acids over c-CeO2 and o-CeO2 supported Pd cat-alysts were significantly accelerated compared with that of MCAA, while the dechlorination of trichloroacetic acid (TCAA) was remarkably depressed over dp-Pd1/r-CeO2 due to the weak affinity of the catalyst surface for TCAA.