NH3-SCR over Cu-zeolite catalysts: activity and deactivation studies
Doktorsavhandling, 2017

NOx emission is one of the major contributors to air pollution especially in the urban environment. The most frequently applied technique to reduce NOx from diesel engine is to employ ammonia selective catalytic reduction (NH3-SCR) using Cu‑zeolite as the catalyst. The major challenge for zeolite-based materials is their susceptibility towards hydrothermal aging. The impact of hydrothermal treatment was investigated using Cu‑Beta aged at 500-900 ⁰C. Although the zeolite structure was still intact after aging up to 800 ⁰C, the SCR activity was readily affected by the aging; however, this effect was less than that of the oxidation reactions. Further, a structure collapse was observed after aging at 900 ⁰C. A comparison study between the activity of the large-pore zeolite, Cu‑Beta and the small-pore zeolite/ silicoaluminophospate, Cu‑SAPO‑34 and Cu‑SSZ‑13, was performed.  In general, Cu‑CHA catalysts showed a higher activity at 150 ⁰C and a lower N2O production than Cu‑Beta did. During low temperature SCR in the presence of NO2, more stable ammonium nitrate species were observed in Cu‑CHA catalysts resulting in a lower conversion of NOx than in Cu‑Beta.  Sulfur poisoning has been known to degrade the activity of Cu‑zeolite catalysts which in this study were investigated using Cu‑SAPO‑34 and Cu‑SSZ‑13. The standard SCR reaction especially at low temperature was severely altered by SO2 poisoning, whereas a lower level of impact was noticeable on SCR reactions in the presence of NO2. A lowering of the reducibility of copper species was found in the sulfated samples, implying that the sites on which the reactions occurred were influenced. A greater effect at low temperature was observed when the poisoning was performed under SCR conditions than in the presence of O2 and H2O only. Moreover, some of the activities could be recovered by performing repeated SCR reactions. In addition, the SO2 treatment under SCR conditions also suppressed the oxidation reactions at low temperature. The temperature programmed desorption (TPD) experiment demonstrated that a larger amount of copper sulfate species was observed when the SO2 exposure was conducted in the presence of H2O than in dry environment. When the SO2 treatment was performed in the presence of NH3, ammonium sulfate species were formed and their formation was not affected by the presence of NO and NO2. Copper sulfate species were found to be more strongly attached to the surface than ammonium sulfate species were. In addition, hydrothermal aging at 800 ⁰C lowered the formation of ammonium sulfate species and the aging facilitated the formation of copper sulfate species. The internal mass transfer limitation in the washcoat was studied by performing experiments in constant ratio of total flow to weight of washcoat using Cu‑SSZ‑13 monoliths with different washcoat thickness. The effect of internal diffusion was noticeable in SCR reaction; however, it was not visible in NH3 oxidation owing to the low conversion of NH3 during the reaction.

Cu‑SAPO-34

internal mass transfer limitation

NH3‑SCR

Cu-zeolite

hydrothermal aging

SO2 poisoning

Cu‑Beta

Cu‑SSZ‑13

KC-salen, Kemigården 4, Chalmers
Opponent: Dr. János Szanyi, Institute for Integrated Catalysis, Pacific Northwest National Laboratory, United States

Författare

Kurnia Wijayanti

Chalmers, Kemi och kemiteknik, Kemiteknik, Kemisk reaktionsteknik

Deactivation of Cu-SSZ-13 by SO2 exposure under SCR conditions

Catalysis Science and Technology,; Vol. 6(2016)p. 2565-2579

Artikel i vetenskaplig tidskrift

Comparison of Cu/BEA, Cu/SSZ-13 and Cu/SAPO-34 for ammonia-SCR reactions

Catalysis Today,; Vol. 258(2015)p. 49-

Artikel i vetenskaplig tidskrift

Impact of sulfur oxide on NH3-SCR over Cu-SAPO-34

Applied Catalysis B: Environmental,; Vol. 166(2015)p. 568-579

Artikel i vetenskaplig tidskrift

Mechanistic investigation of hydrothermal aging of Cu-Beta for ammonia SCR

Applied Catalysis B: Environmental,; Vol. 111(2012)p. 58-66

Artikel i vetenskaplig tidskrift

Wijayanti, K, Xie K, Kumar A, Kamasamudram K, Olsson L, Effect of Gas Compositions on SO2 Poisoning over Cu-SSZ-13 Used for NH3 SCR

Wijayanti, K, Kumar A, Kamasamudram K, Olsson L. Effect of Internal Mass Transfer Limitations on Cu-SSZ-13 used for NH3-SCR

Nitrogen oxides (NOx) is one of the major contributors to air pollution especially in the urban environment and during this decade road transport sector contributes to the highest share of the total NOx emitted. For this reason, the efforts to reduce NOx emissions from vehicles continue to be of high importance. The ammonia selective catalytic reduction (NH3-SCR) technique which employs an aqueous urea solution as the reducing agent can nowadays be regarded as the most practical way for reducing NOx in the diesel aftertreatment system. Amongst the materials investigated, copper (Cu) zeolites have demonstrated better performance in a broad temperature interval. This study covers some important aspects in the development of Cu zeolites as the catalyst for NH3-SCR application.

The susceptibility of Cu zeolites towards hydrothermal aging was investigated using Cu-Beta zeolite aged at 500-900 ⁰C. The SCR activity was readily altered by low temperature aging; however, the oxidation reactions were more significantly affected.

The high temperature stable copper chabazite (Cu-CHA) catalysts, such as Cu‑SAPO‑34 and Cu‑SSZ‑13, demonstrated higher activity than Cu‑Beta at low temperature; however, the presence of NO2 in SCR reaction resulted in more stable ammonium nitrate species hindering the activity of Cu-CHA catalysts at low temperature.

Deactivation caused by sulfur is one of the downside features of Cu zeolites which in this thesis, was examined for Cu‑SAPO‑34 and Cu‑SSZ‑13. The deactivation effect was more severe on standard SCR than on SCR in the presence of NO2. After SO2 poisoning, the activity was possible to recover by performing SCR reaction at high temperature. Further, depending on the gas compositions, copper sulfate and ammonium sulfate species were found during SO2 poisoning causing the decrease in catalytic activity.

The performance of monolithic catalyst system such as those used in diesel aftertreatment has been known to be affected both by kinetic reactions and mass transfer limitations. By varying the washcoat thickness and porosity, the presence of mass transfer in the washcoat was examined.

Finally, a deeper understanding of the mechanisms for catalytic reactions will facilitate the development of better catalysts in the future and strengthen the importance of catalysis for sustainable development.

Drivkrafter

Hållbar utveckling

Styrkeområden

Transport

Ämneskategorier

Annan kemiteknik

Annan kemi

ISBN

978-91-7597-565-8

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4246

Utgivare

Chalmers tekniska högskola

KC-salen, Kemigården 4, Chalmers

Opponent: Dr. János Szanyi, Institute for Integrated Catalysis, Pacific Northwest National Laboratory, United States

Mer information

Skapat

2017-04-06