scholarly journals Experimental Study on the Deactivating Effect of KNO3, KCl, and K2SO4on Nanosized Ceria/Titania SCR Catalyst

2015 ◽  
Vol 2015 ◽  
pp. 1-10
Author(s):  
Xiongbo Chen ◽  
Ping Fang ◽  
Wenhao Zeng ◽  
Kunyuan Liu ◽  
Zhixiong Tang ◽  
...  
Keyword(s):  
Oxygen Diffusion ◽  
Surface Defects ◽  
Catalytic Reduction ◽  
Surface Acidity ◽  
Acid Sites ◽  
Ammonia Adsorption ◽  
Scr Catalyst ◽  
No Conversion ◽  
Ceria Reduction ◽  
Potassium Addition

Nanosized Ce/TiO2is effective in selective catalytic reduction of NO with NH3. The NO conversion of Ce/TiO2is 93% at 370°C. However, addition of potassium using KNO3, KCl, or K2SO4as precursors effectively deactivates Ce/TiO2. NO conversion at 370°C is reduced to 45%, 24%, and 16% after addition of KNO3, KCl, and K2SO4, respectively, with a controlled K/Ce molar ration at 0.25. The deactivation may be attributed to the changes in the structural and chemical state of ceria and the degradation of surface acidity. The transformation of amorphous ceria into ceria crystals after potassium addition, together with the decrease of surface defects, is also determined. Oxygen diffusion in the process of ceria reduction is slow, and the redox cycle is slowed down. Moreover, the surface acid sites are markedly destroyed, leading to the reduced capacity of ammonia adsorption. These results may provide useful information for the application and life management of CeO2/TiO2in potassium-rich environments such as biofuel-fired boilers.

Efficiency of Phosphotungstic Acid Modified Mn-Based Catalysts to Promote Activity and N2 Formation for Selective Catalytic Reduction of NO with Ammonia

2019 ◽  
Vol 17 (7) ◽  
Author(s):  
Yongqiang Huang ◽  
Peixin Li ◽  
Runduo Zhang ◽  
Ying Wei
Keyword(s):  
Selective Catalytic Reduction ◽  
Catalytic Reduction ◽  
Acid Sites ◽  
Bronsted Acid ◽  
Brønsted Acid ◽  
Brønsted Acid Sites ◽  
No Conversion ◽  
Brönsted Acid ◽  
Brönsted Acid Sites ◽  
Nitrate Species

Abstract In this work, the modified Mn-based NH3-SCR (NH3 low-temperature selective catalytic reduction) catalysts with excellent NO conversion and N2 selectivity be designed. N2 yield was hardly more than 75 % over MnOx/TiO2 for NH3-SCR reaction, whereas the NH3-SCR performance has been significantly improved by using 50 wt.% HPW (H3PW12O40)-MnOx/TiO2. 100 % NO conversion and more than 95 % N2 yield was obtained in wide operating temperature window (150–400°C), suggesting that the addition of HPW could effectively improve the NO reduction conversion. After that, the catalysts were further characterized by XRD, H2-TPR, XPS and in situ DRIFT. DRIFT analysis implied that the introduction of HPW significantly improve the capacity of NH4 + species adsorbed on Brønsted acid sites accompanied with inhibiting the formation and consumption of nitrite species. It proved that the non-selective catalytic reduction reaction over HPW-MnOx/TiO2 catalysts are restrained. HPW could accelerate the formation and consumption of NH4 + species adsorbed on Brønsted acid sites with deactivation of nitrate species. In addition, NH3(ad) could be hardly oxidized to NH species and then reacted with nitrate species (L-H mechanism) and gaseous NO (E-R mechanism). More importantly, the oxidation of NH3 was also suppressed, which plays a dominate role to form N2O above 300°C. Besides, the deactivation of potassium poisoning on the SCR activity significantly weakened for modified samples compared to parent catalyst.

scholarly journals Deactivation of Cu/SSZ-13 NH3-SCR Catalyst by Exposure to CO, H2, and C3H6

Catalysts ◽  
2019 ◽  
Vol 9 (11) ◽  
pp. 929 ◽  
Author(s):  
Auvray ◽  
Mihai ◽  
Lundberg ◽  
Olsson
Keyword(s):  
Flow Reactor ◽  
Catalytic Reduction ◽  
Plug Flow ◽  
Acid Sites ◽  
Drift Spectroscopy ◽  
Scr Catalyst ◽  
Nh3 Scr ◽  
Scr Catalysts ◽  
Nh3 Oxidation ◽  
Diffuse Reflectance Infrared

Lean nitric oxide (NOx)-trap (LNT) and selective catalytic reduction (SCR) are efficient systems for the abatement of NOx. The combination of LNT and SCR catalysts improves overall NOx removal, but there is a risk that the SCR catalyst will be exposed to high temperatures and rich exhaust during the LNTs sulfur regeneration. Therefore, the effect of exposure to various rich conditions and temperatures on the subsequent SCR activity of a Cu-exchanged chabazite catalyst was studied. CO, H2, C3H6, and the combination of CO + H2 were used to simulate rich conditions. Aging was performed at 800 °C, 700 °C, and, in the case of CO, 600 °C, in a plug-flow reactor. Investigation of the nature of Cu sites was performed with NH3-temperature-programed desorption (TPD) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) of probe molecules (NH3 and NO). The combination of CO and H2 was especially detrimental to SCR activity and to NH3 oxidation. Rich aging with low reductant concentrations resulted in a significantly larger deactivation compared to lean conditions. Aging in CO at 800 °C caused SCR deactivation but promoted high-temperature NH3 oxidation. Rich conditions greatly enhanced the loss of Brønsted and Lewis acid sites at 800 °C, indicating dealumination and Cu migration. However, at 700 °C, mainly Brønsted sites disappeared during aging. DRIFT spectroscopy analysis revealed that CO aging modified the Cu2+/CuOH+ ratio in favor of the monovalent CuOH+ species, as opposed to lean aging. To summarize, we propose that the reason for the increased deactivation observed for mild rich conditions is the transformation of the Cu species from Z2Cu to ZCuOH, possibly in combination with the formation of Cu clusters.

scholarly journals Morphology and Crystal-Plane Effects of Fe/W-CeO2 for Selective Catalytic Reduction of NO with NH3

Catalysts ◽  
2019 ◽  
Vol 9 (3) ◽  
pp. 288 ◽  
Author(s):  
Feihu Liu ◽  
Zhong Wang ◽  
Da Wang ◽  
Dan Chen ◽  
Fushan Chen ◽  
...  
Keyword(s):  
Selective Catalytic Reduction ◽  
Hydrothermal Method ◽  
Surface Area ◽  
Conversion Rate ◽  
Oxygen Vacancies ◽  
Catalytic Reduction ◽  
Acid Sites ◽  
Crystal Surfaces ◽  
Reduction Of No ◽  
No Conversion

The CeO2 ordinary amorphous, nanopolyhedrons, nanorods, and nanocubes were prefabricated by the hydrothermal method, and employed as carriers of Fe/W–CeO2 catalysts to selectively catalyze the reduction of NO with ammonia. Characterization results indicated that the morphology of CeO2 support originated from selectively exposing different crystal surfaces, which has a significant effect on oxygen vacancies, acid sites and the dispersion of Fe2O3. The CeO2 nanopolyhedrons catalyst (Fe/W–CeO2–P) showed most oxygen vacancies, the largest the quantity of acid sites, the largest BET (Brunauer-Emmett-Teller) surface area and the best dispersion of Fe2O3, which was associated with predominately exposing CeO2 (111) planes. Consequently, the Fe/W–CeO2–P catalyst has the highest NO conversion rate in the temperature range of 100–325 °C among the ordinary amorphous, nanorods, and nanocubes Fe/W–CeO2 catalysts.

High-temperature vanadium free catalyst for selective catalytic reduction of NO with NH3 and theoretical study of La2O3 over CeO2/TiO2

2021 ◽  
Author(s):  
Na Wang ◽  
Changfei Ye ◽  
Hui-Dong Xie ◽  
Lei Wang ◽  
Bin Zheng ◽  
...  
Keyword(s):  
High Temperature ◽  
Selective Catalytic Reduction ◽  
Theoretical Study ◽  
Catalytic Reduction ◽  
Impregnation Method ◽  
Scr Catalyst ◽  
Reduction Of No ◽  
No Conversion

High-temperature SCR catalyst of La2O3-CeO2/TiO2 was prepared by an impregnation method. The effect of CeO2 and La2O3 content on the NO conversion was studied and the experiment result showed that...

scholarly journals Research Status and Prospect on Vanadium-Based Catalysts for NH3-SCR Denitration

Materials ◽  
2018 ◽  
Vol 11 (9) ◽  
pp. 1632 ◽  
Author(s):  
Jie Zhang ◽  
Xiangcheng Li ◽  
Pingan Chen ◽  
Boquan Zhu
Keyword(s):  
Active Sites ◽  
Catalytic Mechanism ◽  
Surface Defects ◽  
Catalytic Reduction ◽  
Surface Acidity ◽  
Industrial Applications ◽  
Future Research ◽  
Medium Temperature ◽  
Temperature Range ◽  
Vanadium Based Catalysts

Selective catalytic reduction of NOx with NH3 is one of the most widely used technologies in denitration. Vanadium-based catalysts have been extensively studied for the deNOx process. V2O5/WO3(MoO3)TiO2 as a commercial catalyst has excellent catalytic activity in the medium temperature range. However, it has usually faced several problems in practical industrial applications, including narrow windows of operation temperatures, and the deactivation of catalysts. The modification of vanadium-based catalysts will be the focus in future research. In this paper, the chemical composition of vanadium-based catalysts, catalytic mechanism, the broadening of the temperature range, and the improvement of erosion resistance are reviewed. Furthermore, the effects of four major systems of copper, iron, cerium and manganese on the modification of vanadium-based catalysts are introduced and analyzed. It is worth noting that the addition of modified elements as promoters has greatly improved the catalytic performance. They can enhance the surface acidity, which leads to the increasing adsorption capacity of NH3. Surface defects and oxygen vacancies have also been increased, resulting in more active sites. Finally, the future development of vanadium-based catalysts for denitration is prospected. It is indicated that the main purpose for the research of vanadium-based modification will help to obtain safe, environmentally friendly, efficient, and economical catalysts.

scholarly journals The Influence of the Support on the Activity of Mn–Fe Catalysts Used for the Selective Catalytic Reduction of NOx with Ammonia

Catalysts ◽  
2020 ◽  
Vol 10 (1) ◽  
pp. 63 ◽  
Author(s):  
Irene López-Hernández ◽  
Jesús Mengual ◽  
Antonio Eduardo Palomares
Keyword(s):  
Surface Area ◽  
Active Sites ◽  
Catalytic Reduction ◽  
Catalyst Activity ◽  
High Surface ◽  
High Surface Area ◽  
Acid Sites ◽  
Beta Zeolite ◽  
Ammonia Adsorption ◽  
Fe Catalysts

Mono and bimetallic Mn–Fe catalysts supported on different materials were prepared and their catalytic performance in the NH3–SCR of NOx was investigated. It was shown that Mn and Fe have a synergic effect that enhances the activity at low temperature. Nevertheless, the activity of the bimetallic catalysts depends very much on the support selected. The influence of the support on the catalyst activity has been studied using materials with different textural and acid–base properties. Microporous (BEA-zeolite), mesoporous (SBA15 and MCM41) and bulk (metallic oxides) materials with different acidity have been used as supports for the Mn–Fe catalysts. It has been shown that the activity depends on the acidity of the support and on the surface area. Acid sites are necessary for ammonia adsorption and high surface area produces a better dispersion of the active sites resulting in improved redox properties. The best results have been obtained with the catalysts supported on alumina and on beta zeolite. The first one is the most active at low temperatures but it presents some reversible deactivation in the presence of water. The Mn–Fe catalyst supported on beta zeolite is the most active at temperatures higher than 350 °C, without any deactivation in the presence of water and with a 100% selectivity towards nitrogen.

scholarly journals Promoting Effect of Ti Species in MnOx-FeOx/Silicalite-1 for the Low-Temperature NH3-SCR Reaction

Catalysts ◽  
2020 ◽  
Vol 10 (5) ◽  
pp. 566
Author(s):  
Jialiang Gu ◽  
Rudi Duan ◽  
Weibin Chen ◽  
Yan Chen ◽  
Lili Liu ◽  
...  
Keyword(s):  
Catalytic Reduction ◽  
Surface Acidity ◽  
Space Velocity ◽  
Acid Sites ◽  
Impregnation Method ◽  
Promoting Effect ◽  
Nh3 Scr ◽  
Nh3 Adsorption ◽  
Redox Ability

Manganese and iron oxides catalysts supported on silicalite-1 and titanium silicalite-1 (TS-1) are synthesized by the wet impregnation method for the selective catalytic reduction (SCR) of NOx with NH3 (NH3-SCR), respectively. The optimized catalyst demonstrates an increased NOx conversion efficiency of 20% below 150 °C, with a space velocity of 18,000 h−1, which can be attributed to the incorporation of Ti species. The presence of Ti species enhances surface acidity and redox ability of the catalyst without changing the structure of supporter. Moreover, further researches based on in situ NH3 adsorption reveal that Lewis acid sites linked to Mn4+ on the surface have a huge influence on the improvement of denitration efficiency of the catalyst at low temperatures.

scholarly journals The Deactivation Mechanism of the Mo-Ce/Zr-PILC Catalyst Induced by Pb for the Selective Catalytic Reduction of NO with NH3

Nanomaterials ◽  
2021 ◽  
Vol 11 (10) ◽  
pp. 2641
Author(s):  
Chenxi Li ◽  
Jin Cheng ◽  
Qing Ye ◽  
Fanwei Meng ◽  
Xinpeng Wang ◽  
...  
Keyword(s):  
Selective Catalytic Reduction ◽  
Catalytic Reduction ◽  
Surface Acidity ◽  
Catalyst Activity ◽  
Acid Sites ◽  
Nh3 Scr ◽  
Highly Active ◽  
Negative Effect ◽  
Redox Ability ◽  
Deactivation Mechanism

As a heavy metal, Pb is one component in coal-fired flue gas and is widely considered to have a strong negative effect on catalyst activity in the selective catalytic reduction of NOx by NH3 (NH3-SCR). In this paper, we investigated the deactivation mechanism of the Mo-Ce/Zr-PILC catalyst induced by Pb in detail. We found that NO conversion over the 3Mo4Ce/Zr-PILC catalyst decreased greatly after the addition of Pb. The more severe deactivation induced by Pb was attributed to low surface area, lower amounts of chemisorbed oxygen species and surface Ce3+, and lower redox ability and surface acidity (especially a low number of Brønsted acid sites). Furthermore, the addition of Pb inhibited the formation of highly active intermediate nitrate species generated on the surface of the catalyst, hence decreasing the NH3-SCR activity.

scholarly journals Ferrierite and Its Delaminated Forms Modified with Copper as Effective Catalysts for NH3-SCO Process

Materials ◽  
2020 ◽  
Vol 13 (21) ◽  
pp. 4885
Author(s):  
Aneta Święs ◽  
Małgorzata Rutkowska ◽  
Andrzej Kowalczyk ◽  
Urbano Díaz ◽  
Antonio E. Palomares ◽  
...  
Keyword(s):  
Copper Oxide ◽  
Ammonia Oxidation ◽  
Catalytic Reduction ◽  
Surface Acidity ◽  
Selective Reduction ◽  
Exchange Method ◽  
Copper Species ◽  
Selective Catalytic Oxidation ◽  
Catalytically Active ◽  
Copper Cations

Ferrierites and their delaminated forms (ITQ-6), containing aluminum or titanium in the zeolite framework, were synthetized and modified with copper by an ion-exchange method. The obtained samples were characterized with respect to their chemical composition (ICP-OES), structure (XRD, UV-Vis DRS), textural parameters (N2-sorption), surface acidity (NH3-TPD), form and reducibility of deposited copper species (UV-Vis DRS and H2-TPR). Ferrierites and delaminated ITQ-6 zeolites modified with copper were studied as catalysts for the selective catalytic oxidation of ammonia to dinitrogen (NH3-SCO). It was shown that aggregated copper oxide species, which were preferentially formed on Ti-zeolites, were catalytically active in direct low-temperature ammonia oxidation to NO, while copper introduced into Al-zeolites was present mainly in the form of monomeric copper cations catalytically active in selective reduction of NO by ammonia to dinitrogen. It was postulated that ammonia oxidation in the presence of the studied catalysts proceeds according to the internal-selective catalytic reduction mechanism (i-SCR) and therefore the suitable ratio between aggregated copper oxide species and monomeric copper cations is necessary to obtain active and selective catalysts for the NH3-SCO process. Cu/Al-ITQ-6 presented the best catalytic properties possibly due to the most optimal ratio of these copper species.

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