Chloroform Hydrodechlorination over Palladium-Gold Catalysts: A First-Principles DFT Study

Hydrodechlorination is a promising method for treating toxic chlorocarbon compounds. Pd is among the most effective catalysts for chloroform hydrodechlorination, and experiments have shown that the Pd-Au alloy catalyst yields superior catalytic performance over pure Pd. Here we examine the chloroform hydrodechlorination mechanism over Pd(111) and Pd-ML/Au(111) surfaces using periodic, self-consistent density functional theory calculations (DFT, GGA-PW91) and maximum rate analysis. We suggest that the reaction occurs on both surfaces through complete dechlorination of chloroform followed by hydrogenation of CH* to methane, and that the initial dechlorination step is likely the rate-limiting step. On Pd(111), the chloroform dechlorination barrier is 0.24 eV higher than the desorption barrier, whereas on Pd-ML/Au(111), the chloroform dechlorination barrier is 0.07 eV lower than the desorption barrier, which can explain the higher hydrodechlorination activity of the Pd-Au alloy catalyst.