scholarly journals The poisoning effect of K, Ca and Na on CeZrTiAl catalyst with nanosheet skeleton structure

2021 ◽  
Author(s):  
Qianming Man ◽  
Pijun Gong ◽  
Yifei Jiang ◽  
Yulu Zhang ◽  
Ziqiang Chen ◽  
...  
Keyword(s):  
Catalyst Surface ◽  
Catalytic Reduction ◽  
Acid Sites ◽  
Catalyst Poisoning ◽  
Poisoning Effect ◽  
Chemisorbed Oxygen ◽  
Pore Blockage ◽  
Oxidation Of No ◽  
Critical Reason ◽  
Skeleton Structure

The poisoning effect of KNO3, NaNO3, and Ca(NO3)2 on CeZrTiAl catalyst for selective catalytic reduction of NO with NH3 was investigated. It was found that the activity deactivation rate follows K> Na > Ca. SEM and BET showed that the accumulation of catalysts was severe after poisoning, and the nanosheet γ-Al2O3 skeleton structure disappeared due to alkali coating. The decrease of the specific surface area is accompanied by pore blockage, making the catalyst unable to expose rich reaction sites. In addition, the fewer surface Ce3+ and chemisorbed oxygen on the surface of the poisoned catalyst weaken the cycle between Ce3+ and Ce4+, resulting in bad redox performance. Thus, the failure to realize the efficient oxidation of NO to NO2. Another critical reason for catalyst poisoning failure is that the decrease of surface acid sites seriously affects the adsorption and activation of NH3 and NOx on the catalyst surface.

scholarly journals Poisoning Effects of Phosphorus, Potassium and Lead on V2O5-WO3/TiO2 Catalysts for Selective Catalytic Reduction with NH3

Catalysts ◽  
2020 ◽  
Vol 10 (3) ◽  
pp. 345
Author(s):  
Jifa Miao ◽  
Xianfang Yi ◽  
Qingfa Su ◽  
Huirong Li ◽  
Jinsheng Chen ◽  
...  
Keyword(s):  
Catalytic Reduction ◽  
Active Oxygen Species ◽  
Negative Influence ◽  
Acid Sites ◽  
Active Oxygen ◽  
Oxygen Species ◽  
Poisoning Effect ◽  
The Past ◽  
Nox Conversion ◽  
Vanadium Species

The poisoning effect of single elements on commercial V2O5-WO3/TiO2 catalysts has been studied in the past decades. In this study, the combined effects of two multi-element systems (phosphorus-potassium and phosphorus-lead) on V2O5-WO3/TiO2 catalysts were studied by diverse characterizations. The results show that potassium and lead can result in the deactivation of catalysts to different degrees by reacting with active acid sites and reducing the amount of V5+. However, phosphorus displays slight negative influence on the NOx conversion of the catalyst due to the comprehensive effect of reducing V5+ amount and generating new acid sites. The samples poisoned by phosphorus–potassium and phosphorus–lead have higher NOx conversion than that by potassium or lead, because doped potassium or lead atoms may react with new acid sites generated by phosphate, which liberates more V–OH on the surface of catalysts and reduces the poisoning effects of potassium or lead on vanadium species and active oxygen species.

The promoting effect of noble metal (Rh, Ru, Pt, Pd) doping on the performances of MnOx–CeO2/graphene catalysts for the selective catalytic reduction of NO with NH3at low temperatures

2018 ◽  
Vol 42 (14) ◽  
pp. 11673-11681 ◽  
Author(s):  
Liu Yang ◽  
Xiaochen You ◽  
Zhongyi Sheng ◽  
Dingren Ma ◽  
Danqing Yu ◽  
...  
Keyword(s):  
Selective Catalytic Reduction ◽  
Noble Metal ◽  
Low Temperatures ◽  
Catalytic Reduction ◽  
Acid Sites ◽  
Promoting Effect ◽  
Reduction Of No ◽  
Chemisorbed Oxygen ◽  
Pd Doping

Rh, Ru, Pt or Pd doping on MnOx–CeO2/graphene catalysts increased the amount of chemisorbed oxygen and surface acid sites.

scholarly journals Deactivation Effect of CaO on Mn-Ce/AC Catalyst for SCR of NO with NH3 at Low Temperature

Catalysts ◽  
2020 ◽  
Vol 10 (8) ◽  
pp. 873 ◽  
Author(s):  
Zenghui Su ◽  
Shan Ren ◽  
Zhichao Chen ◽  
Jie Yang ◽  
Yuhan Zhou ◽  
...  
Keyword(s):  
Catalytic Activity ◽  
Activated Carbon ◽  
Low Temperature ◽  
Acid Site ◽  
Catalytic Reduction ◽  
Total Pore Volume ◽  
Bet Surface Area ◽  
Poisoning Effect ◽  
Scr Of No ◽  
Critical Reason

In this study, the poisoning effect of CaO on activated carbon (AC)-based Mn-Ce catalysts was discussed. Loading CaO inhibited the catalytic activity of the catalyst and the NO conversion of the catalyst decreased from 69.5% to 38.2% at 75 °C. The amount of MnO2 in AC surface decreased in the process of loading CaO, which was detrimental to the Selective Catalytic Reduction (SCR) performance of the catalyst. The change of manganese oxide form inhibited generation rate for the chemisorption oxygen and NO2, which was the most critical reason for the decrease of catalytic activity. Besides, loaded CaO entered into the pores of the catalyst, which led to the blockage of the pores and further resulted in the decrease of the Brunauer-Emmett-Teller (BET) surface area and total pore volume. It also destroyed the oxygen-containing functional groups and acid site on the surface of AC. All of these caused the deactivation of Mn-Ce/AC catalyst after loading CaO.

scholarly journals H2O and/or SO2 Tolerance of Cu-Mn/SAPO-34 Catalyst for NO Reduction with NH3 at Low Temperature

Catalysts ◽  
2019 ◽  
Vol 9 (3) ◽  
pp. 289 ◽  
Author(s):  
Guofu Liu ◽  
Wenjie Zhang ◽  
Pengfei He ◽  
Shipian Guan ◽  
Bing Yuan ◽  
...  
Keyword(s):  
Low Temperature ◽  
Reaction Temperature ◽  
Active Sites ◽  
Competitive Adsorption ◽  
Catalytic Reduction ◽  
Acid Sites ◽  
Impregnation Method ◽  
Spent Catalyst ◽  
Poisoning Effect ◽  
Negative Effect

A series of molecular sieve catalysts (Cu–Mn/SAPO-34) with different loadings of Cu and Mn components were prepared by the impregnation method. The deNOx activity of the catalyst was investigated during the selective catalytic reduction (SCR) of NO with NH3 in the temperature range of 120 °C to 330 °C, including the effects of H2O vapors and SO2. In order to understand the poisoning mechanism by the injection of H2O and/or SO2 into the feeding gas, the characteristics of the fresh and spent catalyst were identified by means of Brunner−Emmet−Teller (BET), X-ray Diffraction (XRD), Scanning Electronic Microscopy (SEM) and Thermal Gravity- Differential Thermal Gravity (TG-DTG). The conversion of NO by the catalyst can achieve at 72% under the reaction temperature of 120 °C, while the value reached more than 90% under the temperature between 180 °C and 330 °C. The deNOx activity test shows that the H2O has a reversible negative effect on NO conversion, which is mainly due to the competitive adsorption of H2O and NH3 on Lewis acid sites. When the reaction temperature increases to 300 °C, the poisoning effect of H2O can be negligible. The poisoning effect of SO2 on deNOx activity is dependent on the reaction temperature. At low temperature, the poisoning effect of SO2 is permanent with no recovery of deNOx activity after the elimination of SO2. The formation of (NH4)2SO4, which results in the plug of active sites and a decrease of surface area, and the competitive adsorption of SO2 and NO should be responsible for the loss of deNOx activity over Cu/SAPO-34.

Liquid-phase aldol condensation of cyclohexanone on aluminium and iron oxides

1982 ◽  
Vol 47 (8) ◽  
pp. 2235-2245 ◽  
Author(s):  
Zdeněk Vít ◽  
Lubomír Nondek ◽  
Jaroslav Málek
Keyword(s):  
Iron Oxides ◽  
Aldol Condensation ◽  
Condensation Reaction ◽  
Complex Function ◽  
Acid Sites ◽  
Basic Site ◽  
Catalyst Poisoning ◽  
Iron Hydroxides ◽  
Transient Complex ◽  
Kinetics Of

The kinetics of the aldol condensation of cyclohexanone in decalin were investigated at 210 °C on catalysts prepared by drying and calcining the aluminium and iron hydroxides at 110-850 °C. The effect of catalyst poisoning by benzoic acid and pyridine on the course of the condensation reaction and aldol retroaldolisation was also examined. The kinetics of the cyclohexanone condensation can be described by means of Langmuir-Hinshelwood equations which are in agreement with a mechanism involving adsorption of cyclohexanone on a basic site to form a transient complex, reaction of this complex with a cyclohexanone molecule affording the aldol, the rate determining interaction of the aldol with free basic and acid sites yielding 2-(1-cyclohexen-1-yl)cyclohexanone and water and desorption of these products from the catalyst surface. The proposed kinetic model is supported by the results of catalyst poisoning. The activity of aluminium and iron oxides in the condensation of cyclohexanone is a complex function of their basicity and acidity depending strongly on the calcination temperature.

Solid-state 27Al Nuclear Magnetic Resonance Investigation of Plasma-facilitated NOx Reduction Catalysts

2002 ◽  
Vol 17 (7) ◽  
pp. 1843-1848 ◽  
Author(s):  
Li-Qiong Wang ◽  
Christopher L. Aardahl ◽  
Kenneth G. Rappé ◽  
Diana N. Tran ◽  
Marisol A. Delgado ◽  
...  
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Solid State ◽  
Magnetic Resonance ◽  
Mesoporous Silica ◽  
Catalytic Reduction ◽  
Nox Reduction ◽  
Sodium Aluminate ◽  
Acid Sites ◽  
Structural Defects ◽  
Nuclear Magnetic

Aluminum coordination distribution for alumina catalysts supported on mesoporous silica was examined. It was shown that aluminum coordination correlates to activity of the catalysts for plasma-enhanced, selective catalytic reduction of NOx with propene. Catalysts were prepared by incorporating aluminum onto the surface of a mesoporous silica support via three different post-synthesis routes to produce varying aluminum coordination. Aluminum trichloride, sodium aluminate, and aluminum isopropoxide precursors were examined. High-resolution, solid state 27Al nuclear magnetic resonance was used to determine aluminum coordination distributions for the resulting catalysts. Unsaturated aluminum sites (i.e., structural defects) correlated with increased activity at high temperatures while tetrahedrally-coordinated aluminum or BrØnsted acid sites correlated with activity at low temperatures.

scholarly journals Preparation of Mesoporous Mn–Ce–Ti–O Aerogels by a One-Pot Sol–Gel Method for Selective Catalytic Reduction of NO with NH3

Materials ◽  
2020 ◽  
Vol 13 (2) ◽  
pp. 475
Author(s):  
Yabin Wei ◽  
Shuangling Jin ◽  
Rui Zhang ◽  
Weifeng Li ◽  
Jiangcan Wang ◽  
...  
Keyword(s):  
Selective Catalytic Reduction ◽  
Lewis Acid ◽  
Catalytic Reduction ◽  
Sol Gel ◽  
Acid Sites ◽  
Lewis Acid Sites ◽  
One Pot ◽  
Gel Method ◽  
Nh3 Scr ◽  
Composite Aerogels

Novel Mn–Ce–Ti–O composite aerogels with large mesopore size were prepared via a one-pot sol–gel method by using propylene oxide as a network gel inducer and ethyl acetoacetate as a complexing agent. The effect of calcination temperature (400, 500, 600, and 700 °C) on the NH3–selective catalytic reduction (SCR) performance of the obtained Mn–Ce–Ti–O composite aerogels was investigated. The results show that the Mn–Ce–Ti–O catalyst calcined at 600 °C exhibits the highest NH3–SCR activity and lowest apparent activation energy due to its most abundant Lewis acid sites and best reducibility. The NO conversion of the MCTO-600 catalyst maintains 100% at 200 °C in the presence of 100 ppm SO2, showing the superior resistance to SO2 poisoning as compared with the MnOx–CeO2–TiO2 catalysts reported the literature. This should be mainly attributed to its large mesopore sizes with an average pore size of 32 nm and abundant Lewis acid sites. The former fact facilitates the decomposition of NH4HSO4, and the latter fact reduces vapor pressure of NH3. The NH3–SCR process on the MCTO-600 catalyst follows both the Eley–Rideal (E–R) mechanism and the Langmuir–Hinshelwood (L–H) mechanism.

scholarly journals Mechanism and Performance of the SCR of NO with NH3 over Sulfated Sintered Ore Catalyst

Catalysts ◽  
2019 ◽  
Vol 9 (1) ◽  
pp. 90 ◽  
Author(s):  
Wangsheng Chen ◽  
Fali Hu ◽  
Linbo Qin ◽  
Jun Han ◽  
Bo Zhao ◽  
...  
Keyword(s):  
Photoelectron Spectroscopy ◽  
Catalytic Reduction ◽  
Nox Reduction ◽  
Space Velocity ◽  
Acid Sites ◽  
X Ray Diffraction ◽  
X Ray ◽  
Diffuse Reflectance Infrared Spectroscopy ◽  
And Performance ◽  
Diffuse Reflectance Infrared

A sulfated sintered ore catalyst (SSOC) was prepared to improve the denitration performance of the sintered ore catalyst (SOC). The catalysts were characterized by X-ray Fluorescence Spectrometry (XRF), Brunauer–Emmett–Teller (BET) analyzer, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and diffuse reflectance infrared spectroscopy (DRIFTS) to understand the NH3-selective catalytic reduction (SCR) reaction mechanism. Moreover, the denitration performance and stability of SSOC were also investigated. The experimental results indicated that there were more Brønsted acid sites at the surface of SSOC after the treatment by sulfuric acid, which lead to the enhancement of the adsorption capacity of NH3 and NO. Meanwhile, Lewis acid sites were also observed at the SSOC surface. The reaction between −NH2, NH 4 + and NO (E-R mechanism) and the reaction of the coordinated ammonia with the adsorbed NO2 (L-H mechanism) were attributed to NOx reduction. The maximum denitration efficiency over the SSOC, which was about 92%, occurred at 300 °C, with a 1.0 NH3/NO ratio, and 5000 h−1 gas hourly space velocity (GHSV).

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