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

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.

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MOF-74-M (M = Mn, Co, Ni, Zn, MnCo, MnNi, and MnZn) for Low-Temperature NH3-SCR and In Situ DRIFTS Study Reaction Mechanism

ACS Applied Materials & Interfaces ◽

10.1021/acsami.0c11035 ◽

2020 ◽

Vol 12 (43) ◽

pp. 48476-48485

Author(s):

Shangzhi Xie ◽

Qiuju Qin ◽

Hao Liu ◽

Lijian Jin ◽

Xiaoling Wei ◽

...

Keyword(s):

Reaction Mechanism ◽

Low Temperature ◽

In Situ Drifts ◽

Nh3 Scr

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Insight into the reaction mechanism over PMoA for low temperature NH3-SCR: A combined In-situ DRIFTs and DFT transition state calculations

Journal of Hazardous Materials ◽

10.1016/j.jhazmat.2021.125258 ◽

2021 ◽

Vol 412 ◽

pp. 125258

Author(s):

Yong Jia ◽

Jin Jiang ◽

Ruizi Zheng ◽

Lina Guo ◽

Jing Yuan ◽

...

Keyword(s):

Reaction Mechanism ◽

Low Temperature ◽

Transition State ◽

In Situ Drifts ◽

Nh3 Scr ◽

Insight Into

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Promoting Effect of Mn on In Situ Synthesized Cu-SSZ-13 for NH3-SCR

Catalysts ◽

10.3390/catal10121375 ◽

2020 ◽

Vol 10 (12) ◽

pp. 1375

Author(s):

Jinpeng Du ◽

Jingyi Wang ◽

Xiaoyan Shi ◽

Yulong Shan ◽

Yan Zhang ◽

...

Keyword(s):

Low Temperature ◽

Active Sites ◽

Catalytic Reduction ◽

Acid Sites ◽

Promoting Effect ◽

Nh3 Scr ◽

Temperature Programmed ◽

Diffuse Reflectance Infrared ◽

Redox Ability

The effect of Mn impregnation on the NH3-SCR (selective catalytic reduction of NOx by NH3) activity of in situ synthesized Cu-SSZ-13 was investigated in this work. It was found that Mn addition could efficiently improve the low-temperature activity of Cu-SSZ-13. The optimal amount of Mn was 5 wt.%, and NOx conversion was improved by more than 20% over a temperature range of 120 °C to 150 °C. SEM (scanning electron microscopy), XRD (X-ray diffraction), N2 adsorption-desorption, H2-TPR (temperature programmed reduction of H2), NH3-TPD (temperature programmed desorption of NH3) and in situ DRIFTS (diffuse reflectance infrared Fourier transform spectroscopy) experiments were conducted to investigate the changes in the zeolite structure, active sites, acid sites and reaction mechanism. The impregnated MnOx species caused a decline in the crystallinity of Cu-SSZ-13 but markedly improved the redox ability. Nitrate and nitrite species were observed in the Mn-modified Cu-SSZ-13, and the formation of these species was thought to cause the observed increase in low-temperature NH3-SCR activity. The results show that the addition of Mn is a promising method for promoting the low-temperature catalytic activity of Cu-SSZ-13.

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Improving the Performance of Gd Addition on Catalytic Activity and SO2 Resistance over MnOx/ZSM-5 Catalysts for Low-Temperature NH3-SCR

Catalysts ◽

10.3390/catal11030324 ◽

2021 ◽

Vol 11 (3) ◽

pp. 324

Author(s):

Jinkun Guan ◽

Lusha Zhou ◽

Weiquan Li ◽

Die Hu ◽

Jie Wen ◽

...

Keyword(s):

Catalytic Activity ◽

Low Temperature ◽

Photoelectron Spectroscopy ◽

Active Sites ◽

Molar Ratio ◽

Manganese Sulfate ◽

Nh3 Scr ◽

So2 Resistance ◽

Temperature Programmed

SO2 poisoning is a great challenge for the practical application of Mn-based catalysts in low-temperature selective catalytic reduction (SCR) reactions of NOx with NH3. A series of Gadolinium (Gd)-modified MnOx/ZSM-5 catalysts were synthesized via a citric acid–ethanol dispersion method and evaluated by low-temperature NH3-SCR. Among them, the GdMn/Z-0.3 catalyst with the molar ratio of Gd/Mn of 0.3 presented the highest catalytic activity, in which a 100% NO conversion could be obtained in the temperature range of 120–240 °C. Furthermore, GdMn/Z-0.3 exhibited good SO2 resistance compared with Mn/Z in the presence of 100 ppm SO2. The results of Brunauer–Emmett–Teller (BET), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction of H2 (H2-TPR) and temperature-programmed desorption of NH3 (NH3-TPD) illustrated that such catalytic performance was mainly caused by large surface area, abundant Mn4+ and surface chemisorbed oxygen species, strong reducibility and the suitable acidity of the catalyst. The in situ diffuse reflectance infrared Fourier transform spectra (DRIFTS) results revealed that the addition of Gd greatly inhibited the reaction between the SO2 and MnOx active sites to form bulk manganese sulfate, thus contributing to high SO2 resistance. Moreover, in situ DRIFTS experiments also shed light on the mechanism of low-temperature SCR reactions over Mn/Z and GdMn/Z-0.3, which both followed the Langmuir–Hinshelwood (L–H) and Eley–Rideal (E–R) mechanism.

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Insight into the Promoting Role of Er Modification on SO2 Resistance for NH3-SCR at Low Temperature over FeMn/TiO2 Catalysts

Catalysts ◽

10.3390/catal11050618 ◽

2021 ◽

Vol 11 (5) ◽

pp. 618

Author(s):

Huan Du ◽

Zhitao Han ◽

Xitian Wu ◽

Chenglong Li ◽

Yu Gao ◽

...

Keyword(s):

Low Temperature ◽

Catalyst Surface ◽

Impregnation Method ◽

In Situ Drifts ◽

Tio2 Catalyst ◽

Nh3 Scr ◽

Nh3 Adsorption ◽

So2 Resistance ◽

Fast Scr

Er-modified FeMn/TiO2 catalysts were prepared through the wet impregnation method, and their NH3-SCR activities were tested. The results showed that Er modification could obviously promote SO2 resistance of FeMn/TiO2 catalysts at a low temperature. The promoting effect and mechanism were explored in detail using various techniques, such as BET, XRD, H2-TPR, XPS, TG, and in-situ DRIFTS. The characterization results indicated that Er modification on FeMn/TiO2 catalysts could increase the Mn4+ concentration and surface chemisorbed labile oxygen ratio, which was favorable for NO oxidation to NO2, further accelerating low-temperature SCR activity through the “fast SCR” reaction. As fast SCR reaction could accelerate the consumption of adsorbed NH3 species, it would benefit to restrain the competitive adsorption of SO2 and limit the reaction between adsorbed SO2 and NH3 species. XPS results indicated that ammonium sulfates and Mn sulfates formed were found on Er-modified FeMn/TiO2 catalyst surface seemed much less than those on FeMn/TiO2 catalyst surface, suggested that Er modification was helpful for reducing the generation or deposition of sulfate salts on the catalyst surface. According to in-situ DRIFTS the results of, the presence of SO2 in feeding gas imposed a stronger impact on the NO adsorption than NH3 adsorption on Lewis acid sites of Er-modified FeMn/TiO2 catalysts, gradually making NH3-SCR reaction to proceed in E–R mechanism rather than L–H mechanism. DRIFTS.

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