Periodic, density functional theory calculations were employed to understand the hydrodechlorination of trichloroethylene (TCE) over different facets of a palladium catalyst. In order to accomplish this, the Pd surface was modelled as terrace sites (Pd(111)) and undercoordinated sites (Pd (211), Pd (100) and Pd (110)). The most stable binding configuration of TCE on the Pd surface was found to be through the di-σ mode of binding, wherein each carbon atom of the TCE molecule sits on top of the Pd atom [Figure 1]. Comparing TCE adsorption over Pd facets, TCE shows the highest binding energy of -178 kJ/mol over Pd (110) [Figure 1d]. TCE, upon adsorption on Pd, immediately undergoes dechlorination followed by subsequent hydrogenation of the hydrocarbon intermediates as the activation energies for C-Cl bond dissociation steps were quite low in comparison to the hydrogenation steps. As a result, the catalyst tends to undergo poisoning due to the chlorine atoms accumulated on the surface. Chlorine binds to the Pd facets as follows: Pd (110) &gt; Pd (211) &gt; Pd (100) &gt; Pd (111), indicating rapid poisoning of the undercoordinated sites in comparison to the terrace site. The strongly adsorbed Cl atoms react with hydrogen to form HCl.

Understanding hydrodechlorination of trichloroethylene on different facets of a Pd catalyst using DFT simulations

ACS Spring Meeting 2021

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