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Origin of potassium promotion effects on CuCl2/gamma-Al2O3 catalyzed ethylene oxychlorination

Abstract

Potassium promoters are widely used in industrial catalysts of ethylene oxychlorination to achieve optimum performance. However, the origin of the promoter effect is not fully understood. Herein, we investigated the potassium promotion effect on CuCl2/γ-Al2O3 catalyzed ethylene oxychlorination by kinetic experiments and DFT calculations. Kinetic experiments observed the effect of KCl on individual steps, and the evolution of the reaction mechanisms with Cl/Cu ratios. Further exploration via DFT found that KCl increases the formation energy of Cl vacancy (ΔE_v) and thus inhibits the reduction activity, which is attributed to the shift-down of Bader charge of Cl. E_v boosts with the decline of Cl/Cu ratios; thus, ethylene can extract Cl atoms from the surface with a Cl/Cu ratio of 2, while it anchors to metal atoms at lower Cl/Cu ratios. The distinct adsorption modes reflect the evolution of reaction mechanisms with Cl/Cu ratios. KCl facilitates the adsorption of oxygen owing to the shift-up of the Bader charge of Cu atom. Potassium reduces the Gibbs free energy barrier of the oxidation step, which agrees with the experimental observation. It is concluded that the potassium promoter effect on the catalytic performance mainly results from the modification of the charge of surface atoms.
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Category

Academic article

Language

English

Author(s)

  • Yanying Qi
  • Endre Fenes
  • Hongfei Ma
  • Yalan Wang
  • Kumar Ranjan Rout
  • Terje Fuglerud
  • Piccinini Marco
  • De Chen

Affiliation

  • SINTEF Industry / Process Technology
  • Belgium
  • Norwegian University of Science and Technology
  • INOVYN Norge

Year

2020

Published in

Applied Surface Science

ISSN

0169-4332

Volume

521

View this publication at Norwegian Research Information Repository