New Insight into the In Situ SO2 Poisoning Mechanism over Cu-SSZ-13 for the Selective Catalytic Reduction of NOx with NH3

Yu Qiu,Wentian Yi,Jiazhe Chen,Chi Fan,Xiaoxue Niu,Changcheng Sun,Hongchang Zhu,Jianjun Chen,Yue Peng,Luyao Guo,Junhua Li,Tao Zhang

doi:10.3390/catal10121391

Abstract

To reveal the nature of SO2 poisoning over Cu-SSZ-13 catalyst under actual exhaust conditions, the catalyst was pretreated at 200 and 500 °C in a flow containing NH3, NO, O2, SO2, and H2O. Brunner−Emmet−Teller (BET), X-ray diffraction(XRD), thermo gravimetric analyzer (TGA), ultraviolet Raman spectroscopy (UV Raman), temperature-programmed reduction with H2 (H2-TPR), temperature-programmed desorption of NO+O2 (NO+O2-TPD), NH3-TPD, in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS), and an activity test were utilized to monitor the changes of Cu-SSZ-13 before and after in situ SO2 poisoning. According to the characterization results, the types and generated amount of sulfated species were directly related to poisoning temperature. Three sulfate species, including (NH4)2SO4, CuSO4, and Al2(SO4)3, were found to form on CZ-S-200, while only the latter two sulfate species were observed over CZ-S-500. Furthermore, SO2 poisoning had a negative effect on low-temperature selective catalytic reduction (SCR) activity, which was mainly due to the sulfation of active sites, including Z2Cu, ZCuOH, and Si-O(H)-Al. In contrast, SO2 poisoning had a positive effect on high-temperature SCR activity, owing to the inhibition of the NH3 oxidation reaction. The above findings may be a useful guideline to design excellent SO2-resistant Cu-based zeolite catalysts.

Highlights

For a decade or so, Cu-SSZ-13 zeolite with a chabazite (CHA) topological structure has been extensively used/investigated for the ammonia selective catalytic reduction of NOx (NH3 -SCR) from diesel engine emissions [1,2,3]
Weight loss at 500–800 ◦ C was observed over CZ-S-200 and CZ-S-500, which can be ascribed to the decomposition of CuSO4 species [14]
A slight weight loss above 800 ◦ C was observed over CZ-S-200 and CZ-S-500, which can be due to the decomposition of Al2 (SO4 )3 species [13]

Summary

Introduction

For a decade or so, Cu-SSZ-13 zeolite with a chabazite (CHA) topological structure has been extensively used/investigated for the ammonia selective catalytic reduction of NOx (NH3 -SCR) from diesel engine emissions [1,2,3]. Cu species in Cu-SSZ-13 are present as two types [8,9]: (1) Cu2+ ions balanced by two adjacent negative framework charges (Z2 Cu) of the 6-membered ring; (2) [Cu(OH)]+ species balanced by one negative framework charge (ZCuOH) of the 8-membered ring. These active Cu species could transform into other active-type species under different conditions, such as [(NH3 ) CuII -O2 -CuII (NH3 )2 ] species [10]. The impact of SO2 poisoning on the selective catalytic reduction (SCR) performance of Cu-SSZ-13 and the corresponding deactivation mechanism have been investigated and can be summarized as follows: (1) low-temperature SCR activity was severely influenced, while high-temperature SCR activity seemed almost unaffected [11]

Methods

Results

Discussion

Conclusion