scholarly journals Numerical Investigation on the Intraphase and Interphase Mass Transfer Limitations for NH3-SCR over Cu-ZSM-5

Processes ◽  
2021 ◽  
Vol 9 (11) ◽  
pp. 1966
Author(s):  
Shiyong Yu ◽  
Jichao Zhang
Keyword(s):  
Pressure Drop ◽  
Catalytic Reduction ◽  
Nox Reduction ◽  
Catalytic Performance ◽  
No Oxidation ◽  
Relative Pressure ◽  
Nh3 Scr ◽  
Nox Conversion ◽  
Nh3 Adsorption ◽  
Media Channels

A systematic modeling approach was scrutinized to develop a kinetic model and a novel monolith channel geometry was designed for NH3 selective catalytic reduction (NH3-SCR) over Cu-ZSM-5. The redox characteristic of Cu-based catalysts and the variations of NH3, NOx concentration, and NOx conversion along the axis in porous media channels were studied. The relative pressure drop in different channels, the variations of NH3 and NOx conversion efficiency were analyzed. The model mainly considers NH3 adsorption and desorption, NH3 oxidation, NO oxidation, and NOx reduction. The results showed that the model could accurately predict the NH3-SCR reaction. In addition, it was found that the Cu-based zeolite catalyst had poor low-temperature catalytic performance and good high-temperature activity. Moreover, the catalytic reaction of NH3-SCR was mainly concentrated in the upper part of the reactor. In addition, the hexagonal channel could effectively improve the diffusion rate of gas reactants to the catalyst wall, reduce the pressure drop and improve the catalytic conversion efficiencies of NH3 and NOx.

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

Materials ◽  
2018 ◽  
Vol 11 (8) ◽  
pp. 1307 ◽  
Author(s):  
Yaping Zhang ◽  
Xiupeng Yue ◽  
Tianjiao Huang ◽  
Kai Shen ◽  
Bin Lu
Keyword(s):  
Selective Catalytic Reduction ◽  
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.

scholarly journals Modified Zeolite Catalyst for a NOx Selective Catalytic Reduction Process in Nitric Acid Plants

Catalysts ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 450
Author(s):  
Magdalena Saramok ◽  
Agnieszka Szymaszek ◽  
Marek Inger ◽  
Katarzyna Antoniak-Jurak ◽  
Bogdan Samojeden ◽  
...  
Keyword(s):  
Nitric Acid ◽  
Selective Catalytic Reduction ◽  
Catalytic Reduction ◽  
Nox Reduction ◽  
Reduction Process ◽  
Active Phase ◽  
Catalytic Performance ◽  
Temperature Range ◽  
Nh3 Scr ◽  
Modified Clinoptilolite

Natural zeolite of the heulandite-type framework was modified with iron and tested as a catalyst for the selective catalytic reduction of nitrogen oxides with ammonia (NH3-SCR) in the temperature range of 150–450 °C. The catalyst was prepared at a laboratory scale in a powder form and then the series of experiments of its shaping into tablets was conducted. Physicochemical studies of the catalyst (N2 sorption at −196 °C, FT-IR, XRD, UV-vis) were performed to determine the textural and structural properties and identify the surface functional groups, the crystalline structure of the catalysts and the form and aggregation of the active phase. The activity tests over the shaped catalyst were performed industry-reflecting conditions, using tail gases from the pilot nitric acid plant. The influence of a temperature, catalyst load, and the amount of reducing agent (ammonia) on the NOx reduction process were investigated. The results of catalytic tests that were performed on model gas mixture showed that non-modified clinoptilolite exhibited around 58% conversion of NO at 450 °C. The temperature window of the shaped catalyst shifted to a higher temperature range in comparison to the powder sample. The catalytic performance of the shaped Fe-clinoptilolite in the industry-reflecting conditions was satisfactory, especially at 450 °C. Additionally, it was observed that the ratio of N2O concentration downstream and upstream of the catalytic bed was below 1, which indicated that the catalyst exhibited activity in both DeNOx and DeN2O process.

scholarly journals Copper-Iron Bimetal Ion-Exchanged SAPO-34 for NH3-SCR of NOx

Catalysts ◽  
2020 ◽  
Vol 10 (3) ◽  
pp. 321 ◽  
Author(s):  
Tuan Doan ◽  
Phong Dam ◽  
Khang Nguyen ◽  
Thanh Huyen Vuong ◽  
Minh Thang Le ◽  
...  
Keyword(s):  
Active Sites ◽  
Catalytic Reduction ◽  
Catalytic Performance ◽  
Physical Structure ◽  
Acid Sites ◽  
Tetraethylammonium Hydroxide ◽  
Nh3 Scr ◽  
Nox Conversion ◽  
Temperature Window ◽  
Scr Of Nox

SAPO-34 was prepared with a mixture of three templates containing triethylamine, tetraethylammonium hydroxide, and morpholine, which leads to unique properties for support and production cost reduction. Meanwhile, Cu/SAPO-34, Fe/SAPO-34, and Cu-Fe/SAPO-34 were prepared through the ion-exchanged method in aqueous solution and used for selective catalytic reduction (SCR) of NOx with NH3. The physical structure and original crystal of SAPO-34 are maintained in the catalysts. Cu-Fe/SAPO-34 catalysts exhibit high NOx conversion in a broad temperature window, even in the presence of H2O. The physicochemical properties of synthesized samples were further characterized by various methods, including XRD, FE-SEM, EDS, N2 adsorption-desorption isotherms, UV-Vis-DRS spectroscopy, NH3-TPD, H2-TPR, and EPR. The best catalyst, 3Cu-1Fe/SAPO-34 exhibited high NOx conversion (> 90%) in a wide temperature window of 250–600 °C, even in the presence of H2O. In comparison with mono-metallic samples, the 3Cu-1Fe/SAPO-34 catalyst had more isolated Cu2+ ions and additional oligomeric Fe3+ active sites, which mainly contributed to the higher capacity of NH3 and NOx adsorption by the enhancement of the number of acid sites as well as its greater reducibility. Therefore, this synergistic effect between iron and copper in the 3Cu-1Fe/SAPO-34 catalyst prompted higher catalytic performance in more extensive temperature as well as hydrothermal stability after iron incorporation.

NO2 Reaction Pathways With NH3 on an Fe-Zeolite SCR Catalyst

2011 ◽  
Author(s):  
Michael A. Smith ◽  
Christopher D. Depcik ◽  
Stefan Klinkert ◽  
John W. Hoard ◽  
Stanislav V. Bohac ◽  
...  
Keyword(s):  
Flow Reactor ◽  
Catalytic Reduction ◽  
Nox Reduction ◽  
Catalyst System ◽  
Lean Nox Trap ◽  
Scr Catalyst ◽  
Nh3 Scr ◽  
Nox Conversion ◽  
Lean Nox ◽  
System Part

One approach for nitrogen oxides (NOx) emission control of medium duty diesel engines is through the use of a combination Lean NOx Trap and Selective Catalytic Reduction (LNT-SCR) catalyst system. In this system, part of the NOx conversion occurs via an NH3 SCR catalyst that is dependent on the NO2 to NOx ratio of the feed gas with NO2 being a more advantageous oxidizer. One benefit of using this system is the conversion of NO to NO2 over the LNT which increases the NO2:NOx ratio of the feed gas to the SCR catalyst. An experimental study has been performed to investigate the NO2-NH3 reaction for an Fe-based zeolite SCR catalyst using a bench top flow reactor. The increase in NO2 concentration at the inlet of the SCR results in the formation of large quantities of N2O from 200°C to 400°C. Further experiments determined that N2O and NH3 react above 350°C. This has led to a hypothesis that one primary SCR reaction (Slow SCR) can be replaced with two reaction steps featuring NH3, NO2, and N2O. As a result, this paper proposes five NOx reduction reactions as part of a global mechanism, which would account for the observed experimental behavior.

scholarly journals Sb-Containing Metal Oxide Catalysts for the Selective Catalytic Reduction of NOx with NH3

Catalysts ◽  
2020 ◽  
Vol 10 (10) ◽  
pp. 1154
Author(s):  
Qian Xu ◽  
Dandan Liu ◽  
Chuchu Wang ◽  
Wangcheng Zhan ◽  
Yanglong Guo ◽  
...  
Keyword(s):  
Metal Oxides ◽  
Selective Catalytic Reduction ◽  
Lewis Acid ◽  
Catalytic Reduction ◽  
No Oxidation ◽  
Bronsted Acid ◽  
Brønsted Acid ◽  
Nh3 Scr ◽  
Brönsted Acid ◽  
Nh3 Adsorption

Sb-containing catalysts (SbZrOx (SbZr), SbCeOx (SbCe), SbCeZrOx (SbCeZr)) were prepared by citric acid method and investigated for the selective catalytic reduction (SCR) of NOx with NH3 (NH3-SCR). SbCeZr outperformed SbZr and SbCe and exhibited the highest activity with 80% NO conversion in the temperature window of 202–422 °C. Meanwhile, it also had good thermal stability and resistance against H2O and SO2. Various characterization methods, such as XRD, XPS, H2-TPR, NH3-TPD, and in situ diffuse reflectance infrared Fourier transform (DRIFT), were applied to understand their different behavior in NOx removal. The presence of Sb in the metal oxides led to the difference in acid distribution and redox property, which closely related with the NH3 adsorption and NO oxidation. Brønsted acid and Lewis acid were evenly distributed on SbCe, while Brønsted acid dominated on SbCeZr. Compared with Brønsted acid, Lewis acid was slightly active in NH3-SCR. The competition between NH3 adsorption and NO oxidation was dependent on SbOx and metal oxides, which were found on SbCe while not on SbCeZr.

scholarly journals The Study of C3H6 Impact on Selective Catalytic Reduction by Ammonia (NH3-SCR) Performance over Cu-SAPO-34 Catalysts

Catalysts ◽  
2021 ◽  
Vol 11 (11) ◽  
pp. 1327
Author(s):  
Yingfeng Duan ◽  
Lina Wang ◽  
Yagang Zhang ◽  
Wei Du ◽  
Yating Zhang
Keyword(s):  
Reaction Rate ◽  
Catalytic Reduction ◽  
Catalytic Performance ◽  
Coke Deposition ◽  
In Situ Drifts ◽  
Nh3 Scr ◽  
Nox Conversion ◽  
Temperature Ranges ◽  
And Performance

In present work, the catalytic performance of Cu-SAPO-34 catalysts with or without propylene during the NH3-SCR process was conducted, and it was found that the de-NOx activity decreased during low temperature ranges (<350 °C), but obviously improved within the range of high temperatures (>350 °C) in the presence of propylene. The XRD, BET, TG, NH3-TPD, NOx-TPD, in situ DRIFTS and gas-switch experiments were performed to explore the propylene effect on the structure and performance of Cu-SAPO-34 catalysts. The bulk characterization and TG results revealed that neither coke deposition nor the variation of structure and physical properties of catalysts were observed after C3H6 treatment. Generally speaking, at the low temperatures (<350 °C), active Cu2+ species could be occupied by propylene, which inhibited the adsorption and oxidation of NOx species, confining the SCR reaction rate and causing the deactivation of Cu-SAPO-34 catalysts. However, with the increase of reaction temperatures, the occupied Cu2+ sites would be recovered and sequentially participate into the NH3-SCR reaction. Additionally, C3H6-SCR reaction also showed the synergetic contribution to the improvement of NOx conversion at high temperature (>350 °C).

Investigation of the Performance of V-W Based Catalysts at Low Temperature for NOx Reduction with NH3

2011 ◽  
Vol 197-198 ◽  
pp. 811-816
Author(s):  
Xin Na Tian ◽  
You Hong Xiao ◽  
Wen Ping Zhang ◽  
Yong Wei Chen
Keyword(s):  
Low Temperature ◽  
Catalytic Reduction ◽  
Nox Reduction ◽  
Potential Method ◽  
Catalytic Performance ◽  
Metal Catalyst ◽  
Impregnation Method ◽  
Operation Temperature ◽  
Nox Conversion ◽  
Temperature Window

The most potential method of selective catalytic reduction (SCR) to remove NOx from diesel engine emissions is very effective in NOx reduction with an efficiency up to 95%. However, the current SCRs have a limitation on operation temperature and a narrow operation temperature window. In this paper, the V-W based catalysts were used in the investigation to improve the low temperature performance of NOx conversion by doping Cu and Mn into V-W based catalyst. The temperature range studied was between 150 °C and 550 °C with an interval of 50 °C. The honeycomb catalysts were prepared by an impregnation method. The study also included characterization of catalysts by BET, XRD, TPD and XPS methods.It is found that NOx conversion performance of the V-W based catalyst increases with the increase of reaction temperature. After the metal Cu or Mn doped into the catalyst, it offers an improvement in the catalytic performance. Among all the catalysts studied, the mixed metal catalyst of Cu-Mn-V-W catalyst is found the most potential one, not only because of its higher NOx conversion rate at a low temperature, but also because of its wider operation temperature window.

scholarly journals Novel Preparation of Cu and Fe Zirconia Supported Catalysts for Selective Catalytic Reduction of NO with NH3

Catalysts ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 55
Author(s):  
Katarzyna Świrk ◽  
Ye Wang ◽  
Changwei Hu ◽  
Li Li ◽  
Patrick Da Costa ◽  
...  
Keyword(s):  
Selective Catalytic Reduction ◽  
Catalytic Reduction ◽  
Supported Catalysts ◽  
Catalytic Performance ◽  
Experimental Conditions ◽  
One Pot ◽  
Nh3 Scr ◽  
Scr Of No ◽  
Temperature Programmed ◽  
Stationary Sources

Copper and iron promoted ZrO2 catalysts were prepared by one-pot synthesis using urea. The studied catalysts were characterized by XRD, N2 physisorption, XPS, temperature-programmed desorption of NH3 (NH3-TPD), and tested by the selective catalytic reduction by ammonia (NH3-SCR) of NO in the absence and presence of water vapor, under the experimental conditions representative of exhaust gases from stationary sources. The influence of SO2 on catalytic performance was also investigated. Among the studied catalysts, the Fe-Zr sample showed the most promising results in NH3-SCR, being active and highly selective to N2. The addition of SO2 markedly improved NO and NH3 conversions during NH3-SCR in the presence of H2O. The improvement in acidic surface properties is believed to be the cause.

scholarly journals The Effect of Tourmaline on SCR Denitrification Activity of MnOx/TiO2 at Low Temperature

Catalysts ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 1020
Author(s):  
Yizhe Helian ◽  
Suping Cui ◽  
Xiaoyu Ma
Keyword(s):  
Low Temperature ◽  
Catalytic Reduction ◽  
Catalytic Performance ◽  
Scr Catalyst ◽  
Highly Efficient ◽  
Nh3 Scr ◽  
Catalytic Material ◽  
Acidic Sites ◽  
Denitrification Activity ◽  
The Stability

Selective catalytic reduction (SCR) technology is the most widely used flue gas denitration technology at present. The stability of a catalyst is the main factor limiting the development of this technology. In this study, an environmentally friendly and highly efficient NH3-SCR catalyst was prepared by coprecipitation method from acidolysis residue of industrial waste and tourmaline. We found that the addition of tourmaline has an important impact on the denitration activity of the catalytic material. The NOx conversion exceeded 97% at 200 °C with the dosage of 10% tourmaline, which is about 7% higher than that without doping. The improvement of catalytic performance was mostly attributed to the permanent electrodes of tourmaline, which effectively promotes the dispersion of MnOx/TiO2 catalytic materials, increases the number of acidic sites and changes the valence distribution of manganese ions in products, which speeds up the diffusion of protons and ions, resulting in the acceleration of redox reaction. These as-developed tourmaline-modified MnOx/TiO2 materials have been demonstrated to be promising as a new type of highly efficient low-temperature NH3-SCR catalyst.

Rapidly Pulsed Reductants for Diesel NOx Reduction With Lean NOx Traps: Comparison of Alkanes and Alkenes as the Reducing Agent

2016 ◽  
Author(s):  
Amin Reihani ◽  
Brent Patterson ◽  
John Hoard ◽  
Galen B. Fisher ◽  
Joseph R. Theis ◽  
...  
Keyword(s):  
Catalytic Reduction ◽  
Nox Reduction ◽  
Oxygen Storage Capacity ◽  
Pulse Frequency ◽  
Oxygen Storage ◽  
Passenger Cars ◽  
Catalyst Composition ◽  
Nox Conversion ◽  
Lean Nox ◽  
Lean Nox Traps

Lean NOx Traps (LNTs) are often used to reduce NOx on smaller diesel passenger cars where urea-based Selective Catalytic Reduction (SCR) systems may be difficult to package. However, the performance of LNTs at temperatures above 400°C needs to be improved. The use of Rapidly Pulsed Reductants (RPR) is a process in which hydrocarbons are injected in rapid pulses ahead of the LNT in order to improve its performance at higher temperatures and space velocities. This approach was developed by Toyota and was originally called Di-Air (Diesel NOx aftertreatment by Adsorbed Intermediate Reductants) [1]. There is a vast parameter space that needs to be explored in order to maximize the NOx conversion at high temperatures and flow rates while minimizing the fuel penalty associated with the hydrocarbon injections. Four parameters were identified as important for RPR operation: (1) the flow field and reductant mixing uniformity; (2) the pulsing parameters including the pulse frequency, duty cycle, and rich magnitude; (3) the reductant type; and (4) the catalyst composition, including the type and loading of precious metal, the type and loading of NOx storage material, and the amount of oxygen storage capacity (OSC). In this study, RPR performance was assessed between 150°C and 650°C with several reductants including dodecane, propane, ethylene, propylene, H2, and CO. A novel injection and mixer system was designed that allowed for the investigation of previously unexplored areas of high frequency injections up to f = 100Hz. Under RPR conditions, H2, CO, dodecane, and C2H4 provided approximately 80% NOx conversion at 500°C, but at 600°C the conversions were significantly lower, ranging from 40 to 55%. The NOx conversion with C3H8 was low across the entire temperature range, with a maximum conversion of 25% near 300°C and essentially no conversion at 600°C. In contrast, C3H6 provided greater than 90% NOx conversion over a broad range of temperature between 280°C and 630°C. Among the hydrocarbons, this suggested that the high temperature NOx conversion with RPR improves as the reactivity of the hydrocarbon increases.

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