The Hydrodechlorination Mechanism of 1,2-Dichloroethane over Platinum Catalysts

The hydrodechlorination mechanism of 1,2-dichloroethane over platinum catalysts

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). However, it is among the many chlorinated hydrocarbon compounds which are highly toxic and carcinogenic ^[1]. An effective and efficient treatment method for the chlorocarbon species in industrial waste streams is highly desired. Catalytic hydrodechlorination, which uses hydrogen to convert chlorinated species into hydrogen chloride and valuable hydrocarbon products, is an attractive approach from both the economic and environmental standpoints. Catalytic hydrodechlorination of 1,2-DCA produces both ethylene and ethane, where ethylene is the desired product due to its higher economic value. 1,2-DCA hydrodechlorination is thus a challenge of both the dechlorination activity and ethylene selectivity. Pt-based catalysts have been studied experimentally for this chemistry. Monometallic Pt yields only saturated hydrocarbon products, while bimetallic Pt alloys such as Pt-Cu, Pt-Sn and Pt-Ag can be highly selectively towards ethylene formation ^{[2] [3]}. The fundamental reason behind the superior performance of these bimetallic catalysts, however, remains unclear. Here, we aim to investigate the reaction mechanism of 1,2-DCA hydrodechlorination from the atomic level using a combined approach of density functional theory (DFT) calculations, microkinetic modelling, and kinetic experiments. 

In this work, we will present our reaction mechanistic study of the monometallic Pt catalyst. First, we perform DFT calculations using Pt(111) as the model for the catalytic surface. Based on the DFT-derived energetics, a comprehensive microkinetic model is constructed, which predicts the reaction rates and surface coverages under realistic reaction environments. Comparing the outcomes from the microkinetic model with the experimental results, we seek to elucidate the nature of the active Pt sites under typical hydrodechlorination reaction conditions, and to identify the actual reaction pathway towards the product formation in the 1,2-DCA reaction mechanism. In the end, we will present a scheme which allows us to screen bimetallic candidates using the appropriate selectivity descriptors. The results offer valuable insights for the rational design of Pt-based catalysts for 1,2-DCA hydrodechlorination.

[1] E. D. Goldberg, Science of the Total Environment 100, 17-28 (1991).

[2] V. I. Kovalchuk and J. L. d'Itri, Applied Catalysis A: General 271, 13-25 (2004).

[3] Y. Han et al., Applied Catalysis B: Environmental, 125, 172–179 (2012).