The Influence of Si/Al Ratios on Adsorption and Desorption Characterizations of Pd/Beta Served as Cold-Start Catalysts

: The majority of NOx is exhausted during the cold-start period for the low temperature of vehicle emissions, which can be solved by using Pd/zeolite catalysts to trap NOx at low temperature and release NOx at a high temperature that must be higher than the operating temperature of selective catalytic reduction catalysts (SCR). In this work, several Pd/Beta catalysts were prepared to identify the influence of Si/Al ratios on NO and C3H6 adsorption and desorption characterizations. The physicochemical properties were identified using N2 physical adsorption, Fourier Transform Infrared Spectroscopy (FT-IR), transmission electron microscopy (TEM), X-ray photo electron spectroscopy (XPS), and Na+ titration, while the adsorption and desorption characterizations were investigated by catalyst evaluation. The results indicated that the amount of dispersed Pd ions, the main active sites for NO and C3H6 adsorption, decreased with the increase of Si/Al ratios. Besides this, the intensity of Brønsted and Lewis acid decreased with the increase of Si/Al ratios, which also led to the decrease of NO and C3H6 adsorption amounts. Therefore, Pd dispersion and the acidic properties of Pd/Beta together determined the adsorption ability of NO and C3H6. Moreover, lower Si/Al ratios resulted in the formation of an additional dispersed Pd cationic species, Pd(OH)+, from which adsorbed NO released at a much lower temperature. Finally, an optimum Si/Al ratio of Pd/Beta was found at around 55 due to the balanced performance between the adsorption amounts and desorption temperature.

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A strategy for constructing highly efficient yolk-shell Ce@Mn@TiOx catalyst with dual active sites for low-temperature selective catalytic reduction of NO with NH3

Chemical Engineering Journal ◽

10.1016/j.cej.2021.129572 ◽

2021 ◽

pp. 129572

Author(s):

Xiaosheng Huang ◽

Fang Dong ◽

Guodong Zhang ◽

Yan Guo ◽

Zhicheng Tang

Keyword(s):

Low Temperature ◽

Selective Catalytic Reduction ◽

Active Sites ◽

Catalytic Reduction ◽

Reduction Of No ◽

Highly Efficient

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

Catalysts ◽

10.3390/catal10121391 ◽

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.

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Low-temperature selective catalytic reduction of NOx with NH3 over metal oxide and zeolite catalysts—A review

Catalysis Today ◽

10.1016/j.cattod.2011.03.034 ◽

2011 ◽

Vol 175 (1) ◽

pp. 147-156 ◽

Cited By ~ 583

Author(s):

Junhua Li ◽

Huazhen Chang ◽

Lei Ma ◽

Jiming Hao ◽

Ralph T. Yang

Keyword(s):

Low Temperature ◽

Metal Oxide ◽

Selective Catalytic Reduction ◽

Catalytic Reduction ◽

Zeolite Catalysts ◽

Reduction Of Nox

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Identification of the Mechanism of NO Reduction with Ammonia (SCR) on Zeolite Catalysts

10.26434/chemrxiv.13134770 ◽

2020 ◽

Author(s):

Konstantin Khivantsev ◽

Ja-Hun Kwak ◽

Nicholas R. Jaegers ◽

Miroslaw A. Derewinski ◽

János Szanyi

Keyword(s):

Active Sites ◽

No Reduction ◽

Catalytic Reduction ◽

Molecular Nitrogen ◽

Acid Sites ◽

Zeolite Catalysts ◽

Catalytic Cycle ◽

Rate Limiting Step ◽

Catalytically Active

Cu/Zeolites catalyze selective catalytic reduction of nitric oxide with ammonia. Although the progress has been made in understanding the rate-limiting step of reaction which is reoxidation of Cu(I)(NH3)2 with oxygen to restore the catalytically active Cu(II) site, the exact NO reduction chemistry remained unknown. Herein, we show that nitrosyl ions NO+ in the zeolitic micropores are the true active sites for NO reduction. They react with ammonia even at below/room temperature producing molecular nitrogen through the intermediacy of N2H+ cation. Isotopic experiments confirm our findings. No copper is needed for this reaction to occur. However, when NO+ reacts, “freed up” Bronsted acid site gets occupied by NH3 to form NH4+ – and so the catalytic cycle stops because NO+ does not form on NH4-Zeolites due to their acid sites being already occupied. Therefore, the role of Cu(II) in Cu/Zeolite catalysts is to produce NO+ by the reaction: Cu(II) + NO à Cu(I) + NO+ which we further confirm spectroscopically. The NO+ then reacts with ammonia to produce nitrogen and water. Furthermore, when Cu(I) gets re-oxidized the catalytic cycle then can continue. Thus, our findings are critical for understanding complete SCR mechanism.

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A Novel MnOx Supported Palygorskite SCR Catalyst for Lower Temperature NO Removal from Flue Gases

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.356-360.974 ◽

2011 ◽

Vol 356-360 ◽

pp. 974-979 ◽

Cited By ~ 1

Author(s):

Xian Long Zhang ◽

Bo Wen Shi ◽

Xue Ping Wu ◽

Wei Ping Jiang ◽

Bao Jun Yang ◽

...

Keyword(s):

Low Temperature ◽

Manganese Oxide ◽

Selective Catalytic Reduction ◽

Catalytic Reduction ◽

Flue Gases ◽

Scr Catalyst ◽

No Removal ◽

Highly Active ◽

Lower Temperature ◽

Scr Of Nox

Palygorskite supported manganese oxide catalysts (MnOx/PG) were prepared for lower temperature selective catalytic reduction (SCR) of NOx by NH3. Catalyst’s SCR activity was estimated at varied temperatures. Catalyst’s properties were characterized by XRD, NH3adsorption and TPD. Results showed that MnOx/PG catalyst was highly active for SCR at low-temperature. It was also found that NH3 was mainly adsorbed on palygorskite in two forms. Weakly adsorbed NH3, which was seldom inhibited by loading of MnOx, but was more favorable to SCR. Whereas strongly adsorbed NH3was more likely to be inhibited by MnOx loading but was inessential for SCR.

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