Effects of NO2 Addition on the NH3-SCR over Small-Pore Cu–SSZ-13 Zeolites with Varying Cu Loadings

Abstract Commercial Cu-exchanged small-pore SSZ-13 (Cu-SSZ-13) zeolite catalysts are highly active for the selective catalytic reduction (SCR) of NOx with NH3, but distinct from other catalyst systems, their activity is unexpectedly inhibited in the presence of NO2. Here, we combined kinetic experiments, in-situ/operando X-ray absorption spectroscopy, and density functional theory (DFT) calculations to obtain direct evidence that under reaction conditions, strong oxidation by NO2 forces Cu ions to exist mainly as fixed framework Cu2+ species (fw-Cu2+), which impede the formation of dynamic binuclear Cu+ species that serve as the main active sites for the standard SCR (SSCR) reaction. As a result, the SSCR reaction is significantly inhibited by NO2 in the zeolite system, and the NO2-involved SCR reaction occurs with an energy barrier higher than that of the SSCR reaction on dynamic binuclear sites. Moreover, the NO2-involved SCR reaction tends to occur at the Brønsted acid sites (BAS) rather than the fw-Cu2+ sites. This work clearly explains the strikingly distinctive selective catalytic behavior in the zeolite system.

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Selective catalytic reduction of NOx with NH3: opportunities and challenges of Cu-based small-pore zeolites

National Science Review ◽

10.1093/nsr/nwab010 ◽

2021 ◽

Author(s):

Yulong Shan ◽

Jinpeng Du ◽

Yan Zhang ◽

Wenpo Shan ◽

Xiaoyan Shi ◽

...

Keyword(s):

Selective Catalytic Reduction ◽

Catalytic Reduction ◽

Hydrothermal Stability ◽

Catalyst Design ◽

Scr Catalyst ◽

Nh3 Scr ◽

Small Pore ◽

Fast Scr ◽

Reduction Of Nox ◽

Significant Opportunity

Abstract Zeolites, as efficient and stable catalysts, are widely used in the environmental catalysis field. Typically, Cu-SSZ-13 with small-pore structure shows excellent catalytic activity for selective catalytic reduction of NOx with ammonia (NH3-SCR) as well as high hydrothermal stability. This review summarizes major advances in Cu-SSZ-13 applied to the NH3-SCR reaction, including the state of copper species, standard and fast SCR reaction mechanism, hydrothermal deactivation mechanism, poisoning resistance, and synthetic methodology. The review gives a valuable summary of new insights on the matching between SCR catalyst design principles and the characteristics of Cu2+-exchanged zeolitic catalysts, highlighting the significant opportunity presented by zeolite-based catalysts. Principles for designing zeolites with excellent NH3-SCR performance and hydrothermal stability are proposed. On the basis of these principles, more hydrothermally stable Cu-AEI and Cu-LTA zeolites are elaborated as well as other alternative zeolites applied to NH3-SCR. Finally, we call attention to the challenges facing Cu-based small-pore zeolites that still need to be addressed.

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Modelling Inhibition Effects of Short-Chain Hydrocarbons on a Small-Pore Cu-Zeolite NH3-SCR Catalyst

Topics in Catalysis ◽

10.1007/s11244-016-0600-4 ◽

2016 ◽

Vol 60 (3-5) ◽

pp. 214-219 ◽

Cited By ~ 1

Author(s):

T. Selleri ◽

I. Nova ◽

E. Tronconi ◽

M. Weibel ◽

V. Schmeißer

Keyword(s):

Short Chain ◽

Scr Catalyst ◽

Nh3 Scr ◽

Small Pore

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Comparative Study of SO2 and SO2/SO3 Poisoning and Regeneration of Cu/BEA and Cu/SSZ-13 for NH3 SCR

Emission Control Science and Technology ◽

10.1007/s40825-021-00203-4 ◽

2021 ◽

Author(s):

Xavier Auvray ◽

Maria Arvanitidou ◽

Åsa Högström ◽

Jonas Jansson ◽

Sheedeh Fouladvand ◽

...

Keyword(s):

Selective Reduction ◽

Sulfur Poisoning ◽

Nh3 Scr ◽

Activity Measurements ◽

Small Pore ◽

Before And After ◽

Fast Scr ◽

Diffuse Reflectance Infrared ◽

Partial Activity ◽

Scr No

AbstractTwo copper-exchanged zeolites, Cu/SSZ-13 and Cu/BEA, were studied as catalysts for the selective reduction of NOx by NH3 (NH3-SCR). Their activities for standard SCR (NOx = NO) and fast SCR (NOx = 50% NO + 50% NO2) were measured before and after sulfur poisoning at 250 °C. The effect of 30 ppm SO2 and a mixture of 24 ppm SO3 + 6 ppm SO2 was evaluated. The repetition of subsequent activity measurements served as regeneration method in SCR conditions. SO2 deactivated Cu/SSZ-13 whereas Cu/BEA was only moderately affected. SO3 led to stronger deactivation of both catalysts than SO2. However, also for this case, the Cu/BEA was significantly less affected than Cu/SSZ-13, even though Cu/BEA contained larger amount of stored sulfur. One possible reason for this could be the large pores of Cu/BEA, where the sulfur species possibly resulted in less sterical hindrance than in the small pore SSZ-13 structure. NH3 temperature-programmed desorption (NH3-TPD) showed no loss of storage sites upon sulfur treatment and subsequent regeneration. Partial activity recovery was observed after a period in SCR conditions at 400 °C and 500 °C. Temperature at 300 °C was insufficient to regenerate the catalysts. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) of NO adsorption suggested that SO2 interacts with the ZCuOH sites on Cu/SSZ-13, causing the strong poisoning.

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