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

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

Soot oxidation in low-O2 and O2-free environments by lanthanum-based perovskites: structural changes and the effect of Ag doping

The use of La-based, Cu (LCO), Mn (LMO) and Fe (LFO) perovskites doped with Ag was studied for potential application as cGPF soot oxidation catalysts. Special emphasis was placed on the effect of the soot, reaction gas composition, changes in rich/lean conditions and the resulting physicochemical changes in the catalyst and their reversibility. The use of a catalyst reduced the soot oxidation temperature significantly in a low-O2 environment and with Ag doping the soot oxidation temperature was decreased by 170 °C in loose contact and 230 °C in tight contact compared to uncatalyzed oxidation. For the soot oxidation in an O2-free environment, the highest oxygen storage capacity was found for LCO and LCAO (1 mol O per molcat). The release of such a high amount of O and reduction of Cu2+ to Cu0 was accompanied by the loss of perovskite structure (LCO → Cu/La2O3), which could be reversed following exposure to a high temperature low-O2 environment

Simultaneous improvement of ammonia mediated NOx SCR and soot oxidation for enhanced SCR-on-Filter application

The integration of NOx reduction and catalytic soot oxidation was investigated for the SCRoF (Selective Catalytic Reduction on Filter) applications. By physically mixing a commercial SCR catalyst (either Fe-ZSM-5 and Cu-ZSM-5) with a soot oxidation catalyst (K/CeO2-PrO2), it was possible to lower the soot oxidation temperature by more than 150 degrees and, by optimizing the catalysts mass ratio in the mixture, NOx conversion simultaneously increased, because NO oxidation induced a fast SCR reaction pathway, unlike during standard SCR. Such an improvement in NOx conversion was more pronounced with the Fe-ZSM-5 than with the Cu-ZSM-5 zeolite, as the latter was more sensitive to the NO2/NOx ratio. In order to make the soot oxidation catalyst inactive towards ammonia oxidation, poisoning of the surface acid sites with 3.0 wt.% K2CO3 (corresponding to only 1.0 wt.% K) was performed. In the soot oxidation and SCR catalysts physical mixture, the soot was oxidized mainly by O2 and the contribution of NO2 to oxidation was negligible, as NO2 itself was a key reactant in the (kinetically much faster) SCR reaction