SO2 deactivation mechanism of NO oxidation and regeneration of the LaCoO3 perovskite

Abstract

The deactivation mechanism and methods to cope with the poisoning by SO₂ of LaCoO₃ perovskite-based NO oxidation catalysts were investigated. The LaCoO₃ perovskite was synthesized by a sol–gel method and the fresh, sulphate-deactivated and regenerated catalysts were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, H₂-and soot-temperature programmed reduction, temperature programmed desorption and diffuse reflectance infrared Fourier transform spectroscopy. The SO₂ poisoning strongly affected the NO oxidation activity. It was demonstrated that the deactivation mechanism proceeds in two stages: initially the active sites with a basic character are blocked by SO₃ and subsequently the lanthanum sulphate salts grow progressively on the surface and cobalt is unaffected. Above 500 °C, the surface bound sulphates become mobile and migrate into the bulk of the catalyst. Several prevention and regeneration methods were proposed and tested. By mixing the catalyst with Ca(OH)₂ as an adsorbent nearly 50% of the original activity was retained. Regeneration by diesel soot was presented here for the first time, where the blocking oxygen can spill over to the soot oxidizing it and releasing the bound sulphur as SO₂ and CO₂. Furthermore, a facile regeneration method was explored by washing the deactivated catalyst to dissolve the small amounts of sulphates on the surface.