Computational Insights into the Mechanism of the Selective Catalytic Reduction of NOx: Fe- Versus Cu-Doped Zeolite Catalysts

Catalytic Reduction ◽

Zeolite Catalysts ◽

Reaction Pathways ◽

Half Cycle ◽

Computational Results ◽

Comprehensive Picture ◽

Cu Catalysts ◽

<div> <div> <div> <p>We computationally investigate the mechanism of the reduction half-cycle of the selective catalytic reduction (SCR) of nitrogen oxides with ammonia. We compare both Fe- and Cu-doped zeolite catalysts and aim at exploring all accessible reaction pathways. From our calculations, a comprehensive picture emerges that unifies sev- eral previous mechanistic proposals. We find that both for Fe and for Cu catalysts, different reaction pathways are feasible, but some of the possible reaction pathways differ in these two cases. Our computational results provide a basis for the inter- pretation of in situ spectroscopic investigations that can possibly distinguish the different mechanistic pathways. </p> </div> </div> </div>

Computational Insights into the Mechanism of the Selective Catalytic Reduction of NOx: Fe- Versus Cu-Doped Zeolite Catalysts

10.26434/chemrxiv.7538720 ◽

2019 ◽

Author(s):

Julian Rudolph ◽

Christoph R. Jacob

Keyword(s):

Catalytic Reduction ◽

Zeolite Catalysts ◽

Reaction Pathways ◽

Half Cycle ◽

Computational Results ◽

Comprehensive Picture ◽

Cu Catalysts ◽

<div> <div> <div> <p>We computationally investigate the mechanism of the reduction half-cycle of the selective catalytic reduction (SCR) of nitrogen oxides with ammonia. We compare both Fe- and Cu-doped zeolite catalysts and aim at exploring all accessible reaction pathways. From our calculations, a comprehensive picture emerges that unifies sev- eral previous mechanistic proposals. We find that both for Fe and for Cu catalysts, different reaction pathways are feasible, but some of the possible reaction pathways differ in these two cases. Our computational results provide a basis for the inter- pretation of in situ spectroscopic investigations that can possibly distinguish the different mechanistic pathways. </p> </div> </div> </div>

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):

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.

In Situ DRIFTS Studies of NH3-SCR Mechanism over V2O5-CeO2/TiO2-ZrO2 Catalysts for Selective Catalytic Reduction of NOx

Materials ◽

10.3390/ma11081307 ◽

2018 ◽

Vol 11 (8) ◽

pp. 1307 ◽

Cited By ~ 11

Author(s):

Yaping Zhang ◽

Xiupeng Yue ◽

Tianjiao Huang ◽

Kai Shen ◽

Bin Lu

Keyword(s):

Catalytic Reduction ◽

Nox Reduction ◽

Oxygen Storage ◽

In Situ Drifts ◽

Nh3 Scr ◽

Nh3 Adsorption ◽

Reduction Of Nox ◽

Zro2 Catalyst

TiO2-ZrO2 (Ti-Zr) carrier was prepared by a co-precipitation method and 1 wt. % V2O5 and 0.2 CeO2 (the Mole ratio of Ce to Ti-Zr) was impregnated to obtain the V2O5-CeO2/TiO2-ZrO2 catalyst for the selective catalytic reduction of NOx by NH3. The transient activity tests and the in situ DRIFTS (diffuse reflectance infrared Fourier transform spectroscopy) analyses were employed to explore the NH3-SCR (selective catalytic reduction) mechanism systematically, and by designing various conditions of single or mixing feeding gas and pre-treatment ways, a possible pathway of NOx reduction was proposed. It was found that NH3 exhibited a competitive advantage over NO in its adsorption on the catalyst surface, and could form an active intermediate substance of -NH2. More acid sites and intermediate reaction species (-NH2), at lower temperatures, significantly promoted the SCR activity of the V2O5-0.2CeO2/TiO2-ZrO2 catalyst. The presence of O2 could promote the conversion of NO to NO2, while NO2 was easier to reduce. The co-existence of NH3 and O2 resulted in the NH3 adsorption strength being lower, as compared to tests without O2, since O2 could occupy a part of the active site. Due to CeO2’s excellent oxygen storage-release capacity, NH3 adsorption was weakened, in comparison to the 1 wt. % V2O5-0.2CeO2/TiO2-ZrO2 catalyst. If NOx were to be pre-adsorbed in the catalyst, the formation of nitrate and nitro species would be difficult to desorb, which would greatly hinder the SCR reaction. All the findings concluded that NH3-SCR worked mainly through the Eley-Rideal (E-R) mechanism.

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 ◽

Catalytic Reduction ◽

Zeolite Catalysts ◽

Selective catalytic reduction of NOx by methane over Co-H-MFI and Co-H-FER zeolite catalysts: characterisation and catalytic activity

Journal of Catalysis ◽

10.1016/s0021-9517(02)00153-7 ◽

2003 ◽

Vol 214 (2) ◽

pp. 179-190 ◽

Cited By ~ 100

Author(s):

C Resini

Keyword(s):

Catalytic Activity ◽

Catalytic Reduction ◽

Zeolite Catalysts ◽

Methane-to-methanol conversion over zeolite Cu-SSZ-13, and its comparison with the selective catalytic reduction of NOx with NH3

Catalysis Science & Technology ◽

10.1039/c7cy02461d ◽

2018 ◽

Vol 8 (4) ◽

pp. 1028-1038 ◽

Cited By ~ 35

Author(s):

Ramon Oord ◽

Joel E. Schmidt ◽

Bert M. Weckhuysen

Keyword(s):

Active Site ◽

Catalytic Reduction ◽

Methanol Conversion ◽

Nuclear Site ◽

Ft Ir ◽

Using in situ FT-IR and operando UV-vis-NIR DRS, performed on a series of different Cu–ion-exchanged SSZ-13 zeolites, both a mono-nuclear site or a dimeric copper active site are consistent for methane-to-methanol activation.