Understanding the origin of structure sensitivity in hydrodechlorination of trichloroethylene on a palladium catalyst

Shenoy, Chaitra S. and Khan, Tuhin S. and Verma, Kirti and Tsige, Mesfin and Jha, Kshitij C. and Haider, M. Ali and Gupta, Shelaka (2021) Understanding the origin of structure sensitivity in hydrodechlorination of trichloroethylene on a palladium catalyst. Reaction Chemistry & Engineering, 6 (12). pp. 2270-2279. ISSN 2058-9883

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Periodic density functional theory (DFT) calculations are employed to understand the origin of structure sensitivity in hydrodechlorination (HDC) of trichloroethylene (TCE) over different facets of a palladium catalyst. The HDC reaction is simulated on the terrace (Pd (111) and Pd (100)) and undercoordinated (Pd (211) and Pd (110)) sites of the Pd catalyst. The most stable binding configuration of TCE on the Pd surfaces is observed to be through the di-σ mode of binding, wherein each carbon atom of the TCE molecule is adsorbed atop of the Pd atom. On comparing TCE adsorption over different facets of Pd, a maximum binding energy of -178 kJ mol-1 is calculated over the Pd (110) surface. TCE, upon adsorption on Pd catalyst, undergoes dechlorination followed by hydrogenation of the hydrocarbon intermediates. The activation energies for C-Cl bond dissociation steps are significantly low when compared to the hydrogenation steps. The chlorine released from dechlorination tends to block the active sites, thereby poisoning the surface with high binding energies (B.E > -160 kJ mol-1) on all the surfaces. The trend in chlorine binding energies on Pd facets follows: Pd (110) > Pd (211) > Pd (100) > Pd (111). The removal of surface chlorine is facilitated by its reaction with surface hydrogen to form hydrogen chloride. The activation energy for hydrogen chloride formation is calculated to be 90 kJ mol-1 and 88 kJ mol-1 on Pd (111) and Pd (100) terrace sites, respectively and 109 kJ mol-1 and 118 kJ mol-1 on the step Pd (211) and corrugated Pd (110) facets, respectively. This suggests the ease of removal of Cl as HCl from the terrace sites as compared to the step and corrugated sites. The structure sensitivity in the TCE HDC reaction could possibly arise due to the differences in the energetics of Cl removal on different Pd facets. This mechanistic understanding could provide a rationale for designing suitable catalysts for the HDC of TCE. This journal is © The Royal Society of Chemistry.

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Item Type: Article
Additional Information: This work is supported by Department of Science and Technology (DST) (DST/TMD-EWO/WTI/2K19/EWFH/2019/ 56(G)). The authors would like to thank the High Performance Computing (HPC) Facility at IIT Delhi for providing computational resources. Support is also acknowledged from IIT Hyderabad Seed Grant and the Department of Energy (STTR Grant DE-SC0018875 to Biena Tech LLC) that has allowed broad academic collaboration in high throughput catalytic discovery for industrial applications.
Uncontrolled Keywords: Binding configuration; Hydrodechlorination; Mode of binding; Palladium catalyst; Pd catalyst; Pd(110); Pd(111); Periodic density functional theory calculations; Structure sensitivity; Terrace sites
Subjects: Chemical Engineering
Divisions: Department of Chemical Engineering
Depositing User: . LibTrainee 2021
Date Deposited: 07 Oct 2022 04:00
Last Modified: 07 Oct 2022 04:00
URI: http://raiith.iith.ac.in/id/eprint/10834
Publisher URL: http://doi.org/10.1039/d1re00252j
OA policy: https://v2.sherpa.ac.uk/id/publication/31829
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