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).