Hammershøi, Peter S.

Janssens, Ton V.W.

Jensen, Anker D.

NOx (NO+NO2) emissions from diesel vehicles are reduced by selective catalytic reduction with NH3 (NH3-SCR) over V2O5- or metal-zeolite-based catalysts. Cu-CHA zeolites are particularly relevant due to their superior low-temperature activity [1]. However, the inevitable presence of SO2 in diesel exhaust causes deactivation of Cu-CHA catalysts [1-3]. As the required lifetime of an SCR catalyst is ca. 10000 h, it is important to know how the activity of the catalyst develops with long-term SO2 exposure, and if catalyst regeneration is an option. It has been shown that the deactivation by SO2 is partially reversible [3]. In this contribution, we focus on the SO2 uptake by the Cu-CHA catalyst, and how the reversible and irreversible deactivation are related to the amount of sulfur in the catalyst

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Downloaded from orbit.dtu.dk on: Mar 29, 2019Lifetime impact of SO2-poisoning of a Cu-CHA catalyst for NH3-SCRHammershøi, Peter Sams; Janssens, Ton V.W.; Jensen, Anker DegnPublication date:2018Document VersionPeer reviewed versionLink back to DTU OrbitCitation (APA):Hammershøi, P. S., Janssens, T. V. W., & Jensen, A. D. (2018). Lifetime impact of SO2-poisoning of a Cu-CHAcatalyst for NH3-SCR. Abstract from The 10th International Conference on Environmental Catalysis, The 3rdInternational Symposium on Catalytic Science and Technology in Sustainable Energy and Environment, Tianjin,China.ICEC&EECAT 2018 Lifetime impact of SO2-poisoning of a Cu-CHA catalyst for NH3-SCR Peter S. Hammershøia,b, Ton V. W. Janssensa, Anker D. Jensenb,* aUmicore Denmark ApS, Nøjsomhedsvej 20, 2800 Kgs. Lyngby, Denmark  bDepartment of Chemical and Biochemical Engineering, Technical University of Denmark, Søltofts Plads B229, 2800 Kgs. Lyngby, Denmark E-mail of corresponding author: aj@kt.dtu.dk Abstract: NOx (NO+NO2) emissions from diesel vehicles are reduced by selective catalytic reduction with NH3 (NH3-SCR) over V2O5- or metal-zeolite-based catalysts. Cu-CHA zeolites are particularly relevant due to their superior low-temperature activity [1]. However, the inevitable presence of SO2 in diesel exhaust causes deactivation of Cu-CHA catalysts [1-3]. As the required lifetime of an SCR catalyst is ca. 10000 h, it is important to know how the activity of the catalyst develops with long-term SO2 exposure, and if catalyst regeneration is an option. It has been shown that the deactivation by SO2 is partially reversible [3]. In this contribution, we focus on the SO2 uptake by the Cu-CHA catalyst, and how the reversible and irreversible deactivation are related to the amount of sulfur in the catalyst.  The long-term effects of SO2 exposure are studied here by measurement of the deactivation of 24 Cu-CHA catalysts (Si/Al = 14.6, 2.4 wt% Cu) obtained by exposure to 50 ppm SO2 at 200, 300, 400 and 500 °C for 1, 5, 15, 30, 60, and 120 h. The total amount of SO2 passing the catalyst in 120 h is comparable to that in the lifetime of a heavy-duty vehicle. The regeneration of the catalysts is determined by measurement of the activity after heating each of the 24 samples to 550 °C in an SO2-free gas for 6 h. The most important effect of exposure to SO2 is a decrease of the NOx conversion in the low-temperature range (200-300 °C). Most of the activity can be regenerated by heating to 550 °C. Fig. 1 shows that deactivation of the Cu-CHA catalysts occurs fast, and already at a total SO2 exposure of 750 ppmh, the final activity levels for both the SO2 exposed and regenerated catalysts has been reached. SO2 exposure leads to a saturated deactivation level in the range 85-95 %, and about 20 % for the regenerated catalysts. Full deactivation of the Cu-CHA has not been observed, suggesting that some of the Cu remains active. The data in Fig. 1 also imply that regeneration at 550 °C in SO2-free gas restores the activity to about 80 % of the fresh catalyst even after 6000 ppmh SO2 exposure, showing that the predominant part of the deactivation by SO2 can be reversed by an active regeneration. The irreversible deactivation can be dealt with by proper dimensioning of the catalyst. ICEC&EECAT 2018 Chemical analysis by ICP-OES of the 24 catalyst samples shows a fast initial increase in S/Cu ratios with SO2 exposure, which coincides with the fast initial deactivation. The S/Cu ratio is never significantly higher than 1, indicating that all S atoms in the deactivated catalysts are associated with the Cu ions. The S/Cu ratios after regeneration at 550 °C are limited to 0.2, and does not depend on the exposure temperature. The S/Cu ratios of the SO2 exposed catalysts reach different levels depending on the exposure temperature. The highest S uptake occurs at 300 °C, which means that the S uptake is actually close to its maximum at typical SCR operating temperatures. 0 2000 4000 60000.00.20.40.60.81.00 2000 4000 60000.00.20.40.60.81.00 2000 4000 60000.00.20.40.60.81.00 2000 4000 60000.00.20.40.60.81.0D) 500 °CB) 300 °CC) 400 °CS/Cu and deactivationSO2 exposed:  S/Cu  DeactivationRegenerated:  S/Cu  DeactivationA) 200 °CS/Cu and deactivationTotal SO2 exposure [ppm*h] Total SO2 exposure [ppm*h] Figure 1 – S/Cu ratio and deactivation as functions of total SO2 exposure, for SO2 exposed and regenerated states of a Cu-CHA catalyst. The SO2 exposures were at A) 200 °C, B) 300 °C, C) 400 °C, and D) 500 °C, and the regeneration always at 550 °C. The level of deactivation was measured at 220 °C. In summary, the deactivation of Cu-CHA builds up fast, and regeneration at 550 °C restores the activity to about 80 % of the original level. Furthermore, the S uptake also increases fast initially to a saturation S/Cu level between 0.5-1, dependent on the exposure temperature. Some Cu remains active, which indicates that certain Cu sites appear to be inert to SO2-poisoning. Key words: NH3-SCR, Cu-CHA, SO2 poisoning, deactivation, regeneration References [1] I. Nova, E. Tronconi, Urea-SCR Technology for deNOx After Treatment of Diesel Exhausts, Springer-Verlag, New York, 2014 [2] Y. Cheng, C. Lambert, D. H. Kim et al., Catal. Today, 151 (2010) 266. [3] P. S. Hammershøi, Y. Jangjou, W. S. Epling et al., Appl. Catal. B, 226 (2018) 38.  

Lifetime impact of SO<sub>2</sub>-poisoning of a Cu-CHA catalyst for NH<sub>3</sub>-SCR

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Lifetime impact of SO<sub>2</sub>-poisoning of a Cu-CHA catalyst for NH<sub>3</sub>-SCR

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