Issue 6, 2019

Site selective adsorption and relocation of SOx in deactivation of Cu–CHA catalysts for NH3-SCR

Abstract

The presence of SO2 in diesel exhaust gases causes severe deactivation of the Cu–CHA catalysts for the reduction of NOx by selective catalytic reduction with ammonia (NH3-SCR). The deactivation of Cu–CHA catalysts after exposure to SO2 at 550 °C for 0.5, 4, 8, 16 and 32 h, and subsequent regeneration in SO2-free gas at 550 °C was related to the site-dependent interactions of SO2 with Cu ions associated with one or two framework Al centers (Z-CuOH or Z2-Cu), as determined by electron paramagnetic resonance (EPR). SO2 primarily interacts with the EPR-silent Z-CuOH sites, but a new, EPR-active Z2-Cu phase develops with SO2 exposure time as well. A part of the original Z2-Cu species remain unaffected by SO2, which is associated with a maximum deactivation level of about 90%. Regeneration at 550 °C leads to the release of most of the SO2 from the Z-CuOH sites and some relocation of sulfur to Z2-Cu sites occurs. The activation energy for NH3-SCR on the SO2 exposed catalysts decreases with S content from about 65 kJ mol−1 to 30 kJ mol−1. For the regenerated catalysts, the activation energy is restored to about 65 kJ mol−1, showing the importance of the Z-CuOH sites for the NH3-SCR reaction.

Graphical abstract: Site selective adsorption and relocation of SOx in deactivation of Cu–CHA catalysts for NH3-SCR

Article information

Article type
Paper
Submitted
25 out 2018
Accepted
04 mar 2019
First published
05 mar 2019

React. Chem. Eng., 2019,4, 1081-1089

Site selective adsorption and relocation of SOx in deactivation of Cu–CHA catalysts for NH3-SCR

P. S. Hammershøi, A. L. Godiksen, S. Mossin, P. N. R. Vennestrøm, A. D. Jensen and T. V. W. Janssens, React. Chem. Eng., 2019, 4, 1081 DOI: 10.1039/C8RE00275D

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