(399c) A DFT-Based Study of Pt-Catalyzed Hydrodechlorination of 1,2-Dichloroethane: Effect of Van Der Waals Interactions

A DFT-Based Study of Pt-Catalyzed
Hydrodechlorination of 1,2-Dichloroethane: Effect of
van der Waals Interactions

L.
Xu¹, E. Stangland², M. Mavrikakis¹

¹Department
of Chemical & Biological Engineering, University of Wisconsin-Madison

²Core
Research and Development, The Dow Chemical Company,
Midland MI

1,2-Dichloroethane
(1,2-DCA) is an important intermediate in industrial chemical processes (e.g.
production of PVC). It is also among the many chlorinated hydrocarbon compounds
which are toxic and carcinogenic.^[1]
An effective and efficient treatment method for 1,2-DCA in the industrial waste
streams is thus highly desired. Current combustion-based chlorocarbon treatment
processes suffer from drawbacks such as high energy cost, generation of other
harmful species and loss of hydrocarbon values.^[2] The catalytic
hydrodechlorination which utilizes hydrogen to convert chlorinated species into
environmentally benign products (hydrogen chloride and hydrocarbons) is an
attractive alternative. Pt-based catalysts have been extensively tested in
experiments for the hydrodechlorination of 1,2-DCA.^[3]
However, the detailed reaction mechanism remains unclear due to the lack of
theoretical investigations.

In this work, we aim to elucidate the hydrodechlorination
mechanism of 1,2-DCA over the monometallic Pt catalyst
using a combined approach of density functional theory (DFT) calculations,
microkinetic modelling, and kinetic experiments. We perform DFT calculations
using Pt(111) as a model for the catalytic surface.
Based on the DFT-derived energetics, a comprehensive microkinetic model is
constructed, and the model predictions are compared with our experimental
results. Our initial DFT-based microkinetic model shows significant discrepancy
with the experiments. Thereby, we introduce van der Waals (vdW)
corrections into our DFT calculations. The vdW
interactions stabilize multiple surface intermediates and transition states,
which leads to a better agreement between theory and experiment. Our work here
helps to elucidate the reaction pathway and the nature of active sites in
Pt-catalyzed 1,2-DCA hydrodechlorination. It also
demonstrates the importance of vdW corrections in
accurately describing the surface energetics of chlorinated hydrocarbon species
using DFT methods.

[1] E. D. Goldberg, Sci. Total Environ. 100, 17–28 (1991).

[2] Y. Liu et al., Appl. Catal. B 29, 61–67 (2001).

[3] V. I. Kovalchuk and J.
L. d'Itri, Appl. Catal.
A 271, 13-25 (2004).