(344g) 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).