Ultra-fast catalytic hydrodechlorination of chloroacetic acids over Pd catalyst supported on CeO2 with exposed (1 1 0) plane

Abstract

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 hydrodechlorination (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 catalysts 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.