Tracking mobile active sites and intermediates in NH3-SCR over zeolite catalysts by impedance-based in situ spectroscopy

2019 ◽  
Vol 4 (6) ◽  
pp. 986-994 ◽  
Author(s):  
Peirong Chen ◽  
Valentina Rizzotto ◽  
Kunpeng Xie ◽  
Ulrich Simon
Keyword(s):  
Active Sites ◽  
Zeolite Catalysts ◽  
In Situ Spectroscopy ◽  
Reaction Intermediates ◽  
Nh3 Scr ◽  
Direct Tracking

Impedance-based in situ spectroscopy allows direct tracking of the mobile active sites and reaction intermediates in NH3-SCR over zeolite catalysts.

scholarly journals In Situ DRIFTS Investigation on CeOx Catalyst Supported by Fly-Ash-Made Porous Cordierite Ceramics for Low-Temperature NH3-SCR of NOX

Catalysts ◽  
2019 ◽  
Vol 9 (6) ◽  
pp. 496 ◽  
Author(s):  
Shaoxin Wang ◽  
Ziwei Chen ◽  
Beini He ◽  
Zheng Yan ◽  
Hao Wang ◽  
...  
Keyword(s):  
Fly Ash ◽  
Low Temperature ◽  
Photoelectron Spectroscopy ◽  
Active Sites ◽  
Supported Catalyst ◽  
Nh3 Scr ◽  
Scr Catalysts ◽  
Cordierite Ceramics ◽  
Porous Cordierite

A series of CeOx catalysts supported by commercial porous cordierite ceramics (CPCC) and synthesized porous cordierite ceramics (SPCC) from fly ash were prepared for selective catalytic reduction of NOx with ammonia (NH3-SCR). A greater than 90% NOx conversion rate was achieved by the SPCC supported catalyst at 250–300 °C when the concentration of loading precursor was 0.6 mol/L (denoted as 0.6Ce/SPCC), which is more advantageous than the CPCC supported ones. The EDS mapping results reveal the existence of evenly distributed impurities on the surface of SPCC, which hence might be able to provide more attachment sites for CeOx particles. Further measurements with temperature programmed reduction by hydrogen (H2-TPR) demonstrate more reducible species on the surface of 0.6Ce/SPCC, thus giving rise to better NH3-SCR performance at a low-temperature range. The X-ray photoelectron spectroscopy (XPS) analyses reveal that the Ce atom ratio is higher in 0.6Ce/SPCC, indicating that a higher concentration of catalytic active sites could be found on the surface of 0.6Ce/SPCC. The in situ diffused reflectance infrared fourier transform spectroscopy (DRIFTS) results indicate that the SCR reactions over 0.6Ce/SPCC follow both Eley-Rideal (E-R) and Langmuir-Hinshelwood (L-H) mechanisms. Hence, the SPCC might be a promising candidate to provide support for NH3-SCR catalysts, which also provide a valuable approach to recycling the fly ash.

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

Catalysts ◽  
2020 ◽  
Vol 10 (12) ◽  
pp. 1391
Author(s):  
Yu Qiu ◽  
Chi Fan ◽  
Changcheng Sun ◽  
Hongchang Zhu ◽  
Wentian Yi ◽  
...  
Keyword(s):  
Selective Catalytic Reduction ◽  
Active Sites ◽  
Catalytic Reduction ◽  
Zeolite Catalysts ◽  
So2 Poisoning ◽  
Negative Effect ◽  
Temperature Programmed ◽  
Diffuse Reflectance Infrared ◽  
Sulfate Species

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.

Understanding the nature of NH3-coordinated active sites and the complete reaction schemes for NH3-SCR using Cu-SAPO-34 catalysts

2021 ◽  
Author(s):  
Guangpeng Yang ◽  
Jingyu Ran ◽  
Xuesen Du ◽  
Xiangmin Wang ◽  
Zhilin Ran ◽  
...  
Keyword(s):  
Low Temperature ◽  
Active Sites ◽  
Zeolite Catalysts ◽  
Copper Species ◽  
Nh3 Scr ◽  
Complete Reaction ◽  
Catalytic Capacity ◽  
Reaction Schemes

Cu-SAPO-34 zeolite catalysts show excellent NH3-SCR performance at low temperature, which is due to the catalytic capacity of copper species.

scholarly journals Strikingly Distinctive NH3-SCR Behavior over Cu-SSZ-13 in the Presence of NO2

2021 ◽  
Author(s):  
Yulong Shan ◽  
Guangzhi He ◽  
Jinpeng Du ◽  
Yu Sun ◽  
Zhongqi Liu ◽  
...  
Keyword(s):  
Active Sites ◽  
Density Functional ◽  
Catalytic Reduction ◽  
Acid Sites ◽  
Zeolite Catalysts ◽  
Nh3 Scr ◽  
Highly Active ◽  
Small Pore ◽  
Standard Scr ◽  
Catalyst Systems

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.

Efficient VOx/Ce1–xTixO2Catalysts for Low-Temperature NH3-SCR: Reaction Mechanism and Active Sites Assessed by in Situ/Operando Spectroscopy

ACS Catalysis ◽  
2017 ◽  
Vol 7 (3) ◽  
pp. 1693-1705 ◽  
Author(s):  
Thanh Huyen Vuong ◽  
Jörg Radnik ◽  
Jabor Rabeah ◽  
Ursula Bentrup ◽  
Matthias Schneider ◽  
...  
Keyword(s):  
Reaction Mechanism ◽  
Low Temperature ◽  
Active Sites ◽  
Operando Spectroscopy ◽  
Nh3 Scr
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