(632h) Hydrodechlorination of Chloro-Organic Contaminants in Drinking Water: Design of Bimetallic Alloy Catalysts

Catalytic treatment of chlorinated contaminants, also known as hydrodechlorination (HDC), is considered to be an effective technique for the removal of these compounds from water. Chlorophenol (4CP) is one such contaminant, formed due to the reaction of phenolics with chlorine, which is used as a disinfectant in water. Experimental studies show that chlorophenol dechlorinates to form phenol over a Pd catalyst. Phenol further undergoes hydrogenation to form cyclohexanone or cyclohexanol. The chlorine atom thus released results in strong binding to the Pd surface and hence, deactivation of the catalyst. Moreover, in our recent study, we have observed relatively easy removal of chlorine as HCl from the terrace sites as compared to the step or corrugated sites owing to lower activation barriers over Pd (100) and Pd (111) surfaces. In the present study, the mechanistic insights into the HDC reaction of 4CP over Pd (111) facet is obtained with periodic density functional theory (DFT) calculations as built in Vienna ab initio simulation package (VASP 6.2.0) and used by our group in prior studies. 4CP binds with an energy of -165 kJ/mol on the Pd (111) surface (Figure (i)). It undergoes dechlorination followed by hydrogen addition to form phenol. In addition, bimetallic catalysts tend to show higher activity compared to the monometallic Pd. Thus, we have made an attempt to design bimetallic catalysts with coinage metals (Cu, Ag and Au) and understand the HDC of 4CP over these formulations. Further, this data is utilized to build a microkinetic model (MKM) to estimate the trends in activity (in terms of turnover frequency (Figure (ii))) and selectivity.