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- Olsson, Louise, 1974, et al.
(författare)
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A kinetic model for sulfur poisoning and regeneration of Cu/SSZ-13 used for NH3-SCR
- 2016
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Ingår i: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 183, s. 394-406
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Tidskriftsartikel (refereegranskat)abstract
- In this study, we have developed a multi-site kinetic model that describes the sulfur poisoning and gradual sulfur removal over Cu/SSZ-13 used for NH3-SCR. Sulfur poisoning was conducted under SCR conditions and thereafter, repeated SCR experiments were conducted to examine the effect of such poisoning and the subsequent gradual removal of sulfur. In addition, the effect of sulfur poisoning was examined on NH3 TPD and ammonia oxidation experiments. The following sites were used in the kinetic model: copper in the six-membered rings as described by S1Cu, copper in the larger cages with S2 and S3 as a site where physisorbed ammonia can attach. Further, ammonia was also adsorbed on the Brönsted sites, represented by S1Brön in the model, but in order not to further complicate the model, small amounts of ammonia storage on Brönsted sites were also lumped into S2. In the model, SO2 was adsorbed on the sites containing copper, which are S1Cu and S2. It should be noted that S1Cu and S2 represents hydrated copper sites. Interestingly, we observed experimentally that ammonia storage was larger after sulfur poisoning compared to before, which is why we added ammonia storage and desorption to the S1Cu-SO2 and S2-SO2 sites. However, ammonia was already adsorbing on the copper site; thus, these steps did not result in increased storage. Consequently, reaction steps were added where additional ammonia was adsorbed to form S1Cu-SO2-(NH3)2 and S2-SO2-(NH3)2 species, which could be interpreted as precursors to ammonium sulfates. Another aspect that must be addressed in the model is the observation in the literature that SO2 is more easily desorbed in SO2+NH3+O2 TPD than SO2+O2 TPD. Reversible reaction steps were therefore added whereby the S1Cu-SO2-NH3 and S2-SO2-NH3 species were decomposed to form SO2. A final reaction step was incorporated into the model to describe the SCR reaction with ammonia attached to the sulfur sites. The developed model could well describe the sulfur poisoning and gradual regeneration during repeated SCR experiments. In addition, the model well described the NH3 TPD and NH3 oxidation before and after sulfur poisoning.
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| 3. |
- Wijayanti, Kurnia, 1979, et al.
(författare)
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Deactivation of Cu-SSZ-13 by SO2 exposure under SCR conditions
- 2016
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Ingår i: Catalysis Science and Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 6:8, s. 2565-2579
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Tidskriftsartikel (refereegranskat)abstract
- A deactivation study of Cu-SSZ-13 has been conducted using SO2 exposure under SCR conditions and examining its effect on different reactions involving NH3-SCR. Several reactions, including NH3 storage/TPD, NO/NH3 oxidation, standard SCR, fast SCR and SCR with 75% NO2, as well as NH3-NO2 storage/TPD, were investigated at a temperature range of 100-400 degrees C after exposing the catalyst to 30 ppm SO2 under SCR conditions at 300 degrees C for 90 min. The catalyst was characterized using XRD, BET, ICP-SFMS and H-2-TPR. The BET surface area and pore volume decreased after the sulfur treatment presumably due to blocking by sulfur and/or ammonium-sulfur species. It was found that sulfur was not uniformly deposited along the monolith channel. The deposition occurred from the inlet towards the outlet, as evident from ICP-SFMS measurements. Part of the sulfur was removed after an SCR experiment up to 400 degrees C. However, this removal was observed only in the inlet half of the sample and not in the outlet. Ammonia TPD experiments revealed that the sulfur poisoning resulted in additional sites that were capable of adsorbing ammonia, resulting in increased ammonia storage. Moreover, standard SCR was significantly deactivated by SO2 poisoning under SCR conditions. Due to the site-blocking effect of the ammonium-sulfur species, fewer copper sites are likely available for the redox SCR cycle. Furthermore, the effect of sulfur poisoning on NH3 oxidation and NO2-SCR as well as N2O production in various SCR reactions were observed. Finally, it was found that the conditions for the sulfur poisoning were critical in which SO2 deactivation under SCR conditions (NH3 + NO+ O-2 + H2O) was more severe compared to SO2 poisoning in O-2 + H2O alone.
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