Determining hydrothermal deactivation mechanisms on Cu/SAPO-34 NH3-SCR catalysts at low- and high-reaction regions: establishing roles of different reaction sites

Chen

ACS Appl. Mater. Interfaces

et al. 2023

The development of selective catalytic reduction catalysts by NH3(NH3-SCR) with excellent low-temperature activity and a wide temperature window is highly demanded but is still very challenging for the elimination of NO x emission from vehicle exhaust. Herein, a series of sulfated modified iron–cerium composite oxide Fe1–x Ce x Oδ-S catalysts were synthesized. Among them, the Fe0.79Ce0.21Oδ-S catalyst achieved the highest NO x conversion of more than 80% at temperatures of 175–375 °C under a gas hourly space velocity of 100000 h–1. Sulfation formed a large amount of sulfate on the surface of the catalyst and provided rich Brønsted acid sites, thus enhancing its NH3 adsorption capacity and improving the overall NO x conversion efficiency. The introduction of Ce is the main determining factor in regulating the low-temperature activity of the catalyst by modulating its redox ability. Further investigation found that there is a strong interaction between Fe and Ce, which changed the electron density around the Fe ions in the Fe0.79Ce0.21Oδ-S catalyst. This weakened the strength of the Fe–O bond and improved the lattice oxygen mobility of the catalyst. During the reaction, the iron–cerium composite oxide catalyst showed higher surface lattice oxygen activity and a faster replenishment rate of bulk lattice oxygen. This significantly improved the adsorption and activation of NO x species and the activation of NH3 species on the catalyst surface, thus leading to the superior low-temperature activity of the catalyst.

Section: Resultsmentioning

confidence: 97%

Revealing the Excellent Low-Temperature Activity of the Fe_1–xCe_xO_δ-S Catalyst for NH₃-SCR: Improvement of the Lattice Oxygen Mobility

Chen

ACS Appl. Mater. Interfaces

et al. 2023

“…Usually, the ratio of adsorbed oxygen to total oxygen (O α /O α + O β ) is used to determine the change of catalyst activity, and according to the following formula, it can also be known that the Ce reaction requires the presence of O α . Ce 3+ combines with O 2 to form O 2– and oxidizes NO to NO 2 , that is, the more the Ce 3+ , the more the NO 2 , which provides a possibility for the Langmuir–Hinshelwood mechanism. , …”

Section: Resultsmentioning

confidence: 99%

“…23 Ce 3+ combines with O 2 to form O 2− and oxidizes NO to NO 2 , that is, the more the Ce 3+ , the more the NO 2 , which provides a possibility for the Langmuir−Hinshelwood mechanism. 24,25 The Nano-Ce 10 -PSDC HF /ZrO 2 catalyst prepared by the hydrothermal method was used. The catalyst was subjected to NO x removal activity tests and characterization techniques including XRD, particle size analysis, BET, SEM, and XPS.…”

Section: Sem Analysismentioning

confidence: 99%

Performance of an SCR Catalyst from Sintering Dust by the Hydrothermal Method and Its Water/Sulfur Resistance

Zhou

et al. 2023

Energy Fuels

Durability is an issue for selective catalytic reduction (SCR) catalysts due to their susceptibility to sulfur and water poisoning. In this study, Nano-Ce 10 -PSDC HF /ZrO 2 was prepared by the hydrothermal method using sintering dust, and the impact of SO 2 or water vapor on its SCR performance was investigated. The denitrification performance of Nano-Ce 10 -PSDC HF /ZrO 2 was better than that of 0.25-Ce 10 -PSDC HF /ZrO 2 prepared by the impregnation method in the entire temperature interval from 80 to 400 °C. The highest denitrification rate of 93.6% was achieved at 280 °C. Nano-Ce 10 -PSDC HF /ZrO 2 had a smaller particle size and uniform dispersion but also formed a high concentration of Ce 3+ and adsorbed oxygen O α on the surface. Additionally, it showed better resistance to water and sulfur than 0.25-Ce 10 -PSDC HF /ZrO 2 . Even when exposed to 8% H 2 O and 400 ppm SO 2 , the denitrification rate of Nano-Ce 10 -PSDC HF /ZrO 2 remained at 82.1% after 4 h. SO 2 is more toxic to SCR catalysts than H 2 O. The effect of water on catalyst activity is partially reversible. Deactivation of SCR by SO 2 is primarily caused by the formation of ammonium sulfate species, with some contribution from competitive adsorption between SO 2 and NO x . In conclusion, the Nano-Ce 10 -PSDC HF /ZrO 2 catalyst exhibited the best SCR performance, with water and sulfur resistance, and effectively utilized sintering dust, which has potential application value.

“…These catalyst powders were wash-coated on the honeycomb cordierite, and the monolithic catalyst was used for the NH 3 -SCR reaction . The detailed procedures are explained in the “Supporting Information”.…”

Section: Methodsmentioning

confidence: 99%

Highlights on Key Roles of Y on the Hydrothermal Stability at 900 °C of Cu/SSZ-39 for NH₃-SCR

Lin

Zhao

et al. 2022

ACS Catal.

Self Cite

The continuously updated after-treatment system of diesel engines drives the selective catalytic reduction of ammonia (NH 3 -SCR) catalysts to withstand hydrothermal stability at higher temperatures (>800 °C). To meet the tightened emission of nitrogen oxides (NO x ), yttrium ions (Y 3+ ) were employed to improve the hydrothermal stability of the Cu/SSZ-39 catalyst at 900 °C. X-ray diffraction, solid nuclear magnetic resonance, H 2 temperature-programmed reduction, NH 3 temperature-programmed desorption, and in situ diffuse reflectance infrared Fourier transform spectra verified the key role of Y 3+ on the stability of the structure of SSZ-39 zeolite and the isolated copper species. In detail, the optimized structural stability at 900 °C of the Y-modified Cu/SSZ-39 catalyst is achieved as a result of the spatial and electronic effects of Y 3+ at ion-exchanged sites. Furthermore, Y 3+ ions in the cages of SSZ-39 zeolite induce more isolated copper species in the double six-member rings of SSZ-39 zeolite. The modified catalyst by 1 wt % Y (Cu/Y 1.0 -SSZ-39) shows the best deNO x performance after hydrothermal aging at 900 °C for 10 h, including higher than 70% NO x conversion at 200−550 °C and the maximum NO x conversion of 94% at 300 °C, which is remarkably higher than the maximum NO x conversion of 38% over Cu/SSZ-39 after same hydrothermal aging. This work provides a vital research strategy for fabricating the extraordinary hydrothermally stabilized Cu-based zeolite catalysts for NH 3 -SCR reaction, which would meet the "near-zero" emission after hydrothermal aging at 900 °C in the future.