High activity and regenerability of a palladium–gold catalyst for chloroform degradation

Abstract

BACKGROUND Chloroform (CF), a common groundwater contaminant, can be degraded in deionized water reductively using Pd and Pd-Au catalysts under mild conditions (room temperature, atmospheric pressure) via hydrodechlorination (HDC). However, the performance of these catalysts under field-like conditions is unknown. This study evaluates the lab-scale performance and optimal operating conditions for flow reactors using Pd/Al2O3 and Pd-Au/Al2O3. RESULTS Both catalysts were active for CF HDC when tested using deionized water and groundwater spiked with CF. The Pd-Au catalyst was ∼263× more active than the Pd catalyst using unbuffered deionized water (1550 mL-gPd−1-min−1 vs 5.89 mL-gPd−1-min−1), and was ∼137× more active using buffered groundwater (1030 mL-gPd−1-min−1 vs 7.53 mL-gPd−1-min−1). The buffer was a carbonate/citrate mixture optimized to prevent pH drop and scale formation from minerals present in groundwater. A catalytic flow process was designed using a buffer co-feed and daily regeneration of the catalyst bed. Pd-Au/Al2O3- and Pd/Al2O3-containing reactors exhibited CF conversions of 65% and 32.5% over 18 days operating at a weight hourly space velocity of 30 h−1. CONCLUSIONS This study provides insights into strategies for long-term operation of catalytic flow reactors to treat CF in groundwater, and shows the higher CF HDC catalytic efficiency of Pd-Au over Pd. © 2015 Society of Chemical Industry