The H2O Effect on Cu Speciation in Cu-CHA-Catalysts for NH3-SCR Probed by NH3 Titration

The present work is focused on the effect of water on NH3 adsorption over Cu-CHA SCR catalysts. For this purpose, samples characterized by different SAR (SiO2/Al2O3) ratios and Cu loadings were studied under both dry and wet conditions. H2O adversely affects NH3 adsorption on Lewis acid sites (Cu ions) over all the tested catalysts, as indicated by the decreased NH3 desorption at low temperature during TPD. Interestingly, the NH3/Cu ratio, herein regarded as an index for the speciation of Cu cations, fell in the range of 3–4 (in the presence of gaseous NH3) or 1–2 (no gaseous NH3) in dry conditions, in line with the formation of different NH3-solvated Cu species (e.g., [CuII(NH3)4]2+ and [CuII(OH)(NH3)3]+ with gaseous NH3, [Z2CuII(NH3)2]2+ and [ZCuII(OH)(NH3)]+ without gaseous NH3). When H2O was fed to the system, on the contrary, the NH3/Cu ratio was always close to 3 (or 1), while the Brønsted acidity was slightly increased. These results are consistent both with competition between H2O and NH3 for adsorption on Lewis sites and with the hydrolysis of a fraction of Z2CuII species into ZCuIIOH.

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The Keggin Structure: An Important Factor in Governing NH3–SCR Activity Over the V2O5–MoO3/TiO2 Catalyst

Catalysis Letters ◽

10.1007/s10562-018-2333-4 ◽

2018 ◽

Vol 148 (4) ◽

pp. 1228-1235 ◽

Cited By ~ 10

Author(s):

Rui Wu ◽

Ningqiang Zhang ◽

Xiaojun Liu ◽

Lingcong Li ◽

Liyun Song ◽

...

Keyword(s):

Low Temperature ◽

Catalytic Reduction ◽

Physicochemical Characteristics ◽

Acid Sites ◽

Keggin Structure ◽

Lewis Acid Sites ◽

Nh3 Scr ◽

Strong Acidity ◽

Ft Ir ◽

Brønsted And Lewis Acid

Abstract Heteropolyacids and their salts have been effectively used in selective catalytic reduction because of the Keggin structure and extraordinarily strong acidity. Catalysts with and without the Keggin structure were synthesized to further investigate the effects of heteropolyoxometallate on low temperature NH3–SCR. XRD, BET, Raman, H2–TPR, NH3–TPD, FT-IR, and SO2–TPD techniques were used to characterize the physicochemical characteristics of the catalysts. Results indicate that catalysts with the Keggin structure had more surface Brönsted and Lewis acid sites, and these catalysts had significantly improved performances in the SCR reaction and in SO2 poisoning resistance. Graphical Abstract

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Insight into the Promoting Role of Er Modification on SO2 Resistance for NH3-SCR at Low Temperature over FeMn/TiO2 Catalysts

Catalysts ◽

10.3390/catal11050618 ◽

2021 ◽

Vol 11 (5) ◽

pp. 618

Author(s):

Huan Du ◽

Zhitao Han ◽

Xitian Wu ◽

Chenglong Li ◽

Yu Gao ◽

...

Keyword(s):

Low Temperature ◽

Catalyst Surface ◽

Impregnation Method ◽

In Situ Drifts ◽

Tio2 Catalyst ◽

Nh3 Scr ◽

Nh3 Adsorption ◽

So2 Resistance ◽

Fast Scr

Er-modified FeMn/TiO2 catalysts were prepared through the wet impregnation method, and their NH3-SCR activities were tested. The results showed that Er modification could obviously promote SO2 resistance of FeMn/TiO2 catalysts at a low temperature. The promoting effect and mechanism were explored in detail using various techniques, such as BET, XRD, H2-TPR, XPS, TG, and in-situ DRIFTS. The characterization results indicated that Er modification on FeMn/TiO2 catalysts could increase the Mn4+ concentration and surface chemisorbed labile oxygen ratio, which was favorable for NO oxidation to NO2, further accelerating low-temperature SCR activity through the “fast SCR” reaction. As fast SCR reaction could accelerate the consumption of adsorbed NH3 species, it would benefit to restrain the competitive adsorption of SO2 and limit the reaction between adsorbed SO2 and NH3 species. XPS results indicated that ammonium sulfates and Mn sulfates formed were found on Er-modified FeMn/TiO2 catalyst surface seemed much less than those on FeMn/TiO2 catalyst surface, suggested that Er modification was helpful for reducing the generation or deposition of sulfate salts on the catalyst surface. According to in-situ DRIFTS the results of, the presence of SO2 in feeding gas imposed a stronger impact on the NO adsorption than NH3 adsorption on Lewis acid sites of Er-modified FeMn/TiO2 catalysts, gradually making NH3-SCR reaction to proceed in E–R mechanism rather than L–H mechanism. DRIFTS.

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

Materials ◽

10.3390/ma13020475 ◽

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.

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Effect of the calcination temperature of cerium–zirconium mixed oxides on the structure and catalytic performance of WO3/CeZrO2 monolithic catalyst for selective catalytic reduction of NOx with NH3

RSC Advances ◽

10.1039/c7ra03054a ◽

2017 ◽

Vol 7 (39) ◽

pp. 24177-24187 ◽

Cited By ~ 15

Author(s):

Haidi Xu ◽

Mengmeng Sun ◽

Shuang Liu ◽

Yuanshan Li ◽

Jianli Wang ◽

...

Keyword(s):

Low Temperature ◽

Selective Catalytic Reduction ◽

Lewis Acid ◽

Mixed Oxides ◽

Catalytic Reduction ◽

Catalytic Performance ◽

Acid Sites ◽

Lewis Acid Sites ◽

Reduction Of Nox ◽

Calcined Temperature

The calcined temperature of the carrier obviously affected SCR activity of catalysts, WO3/Ce0.68Zr0.32O2-500 showed the best low-temperature NH3-SCR activity due to its more Lewis acid sites and stronger redox property.

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A general and inherent strategy to improve the water tolerance of low temperature NH3-SCR catalysts via trace SiO2 deposition

Catalysis Communications ◽

10.1016/j.catcom.2016.06.001 ◽

2016 ◽

Vol 84 ◽

pp. 75-79 ◽

Cited By ~ 12

Author(s):

Shuohan Yu ◽

Ningxin Jiang ◽

Weixin Zou ◽

Lulu Li ◽

Changjin Tang ◽

...

Keyword(s):

Low Temperature ◽

Water Tolerance ◽

Nh3 Scr ◽

Scr Catalysts

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In Situ DRIFTS Investigation on CeOx Catalyst Supported by Fly-Ash-Made Porous Cordierite Ceramics for Low-Temperature NH3-SCR of NOX

Catalysts ◽

10.3390/catal9060496 ◽

2019 ◽

Vol 9 (6) ◽

pp. 496 ◽

Cited By ~ 4

Author(s):

Shaoxin Wang ◽

Ziwei Chen ◽

Beini He ◽

Zheng Yan ◽

Hao Wang ◽

...

Keyword(s):

Fly Ash ◽

Low Temperature ◽

Photoelectron Spectroscopy ◽

Active Sites ◽

Supported Catalyst ◽

Nh3 Scr ◽

Scr Catalysts ◽

Cordierite Ceramics ◽

Porous Cordierite

A series of CeOx catalysts supported by commercial porous cordierite ceramics (CPCC) and synthesized porous cordierite ceramics (SPCC) from fly ash were prepared for selective catalytic reduction of NOx with ammonia (NH3-SCR). A greater than 90% NOx conversion rate was achieved by the SPCC supported catalyst at 250–300 °C when the concentration of loading precursor was 0.6 mol/L (denoted as 0.6Ce/SPCC), which is more advantageous than the CPCC supported ones. The EDS mapping results reveal the existence of evenly distributed impurities on the surface of SPCC, which hence might be able to provide more attachment sites for CeOx particles. Further measurements with temperature programmed reduction by hydrogen (H2-TPR) demonstrate more reducible species on the surface of 0.6Ce/SPCC, thus giving rise to better NH3-SCR performance at a low-temperature range. The X-ray photoelectron spectroscopy (XPS) analyses reveal that the Ce atom ratio is higher in 0.6Ce/SPCC, indicating that a higher concentration of catalytic active sites could be found on the surface of 0.6Ce/SPCC. The in situ diffused reflectance infrared fourier transform spectroscopy (DRIFTS) results indicate that the SCR reactions over 0.6Ce/SPCC follow both Eley-Rideal (E-R) and Langmuir-Hinshelwood (L-H) mechanisms. Hence, the SPCC might be a promising candidate to provide support for NH3-SCR catalysts, which also provide a valuable approach to recycling the fly ash.

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Bulk Vanadium Oxide versus Conventional V2O5/TiO2: NH3–SCR Catalysts Working at a Low Temperature Below 150 °C

ACS Catalysis ◽

10.1021/acscatal.9b02695 ◽

2019 ◽

Vol 9 (10) ◽

pp. 9327-9331 ◽

Cited By ~ 9

Author(s):

Yusuke Inomata ◽

Shinichi Hata ◽

Makoto Mino ◽

Eiji Kiyonaga ◽

Keiichiro Morita ◽

...

Keyword(s):

Low Temperature ◽

Vanadium Oxide ◽

Nh3 Scr ◽

Scr Catalysts

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Transition metal ions regulate the catalytic performance of Ti0.8M0.2Ce0.2O2+x for the NH3-SCR of NO: the acidic mechanism

RSC Advances ◽

10.1039/c4ra11829d ◽

2015 ◽

Vol 5 (10) ◽

pp. 7597-7603 ◽

Cited By ~ 13

Author(s):

Yuesong Shen ◽

Yun Su ◽

Yifan Ma

Keyword(s):

Transition Metal Ions ◽

Catalytic Performance ◽

Acid Sites ◽

Acid Strength ◽

Maximum Activity ◽

Lewis Acid Sites ◽

Nh3 Scr ◽

Scr Of No ◽

Temperature Window ◽

Active Temperature

The maximum activity is dependent on the number of Lewis acid sites, and the active temperature window is dependent on the acid strength.

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Strategies of Coping with Deactivation of NH3-SCR Catalysts Due to Biomass Firing

Catalysts ◽

10.3390/catal8040135 ◽

2018 ◽

Vol 8 (4) ◽

pp. 135 ◽

Cited By ~ 3

Author(s):

◽

Keyword(s):

Flue Gas ◽

High Surface ◽

Sol Gel ◽

Acid Sites ◽

Thin Layers ◽

Catalyst Stability ◽

Main Mode ◽

High Potassium ◽

Nh3 Scr ◽

Scr Catalysts

Firing of biomass can lead to rapid deactivation of the vanadia-based NH3-SCR catalyst, which reduces NOx to harmless N2. The deactivation is mostly due to the high potassium content in biomasses, which results in submicron aerosols containing mostly KCl and K2SO4. The main mode of deactivation is neutralization of the catalyst’s acid sites. Four ways of dealing with high potassium contents were identified: (1) potassium removal by adsorption, (2) tail-end placement of the SCR unit, (3) coating SCR monoliths with a protective layer, and (4) intrinsically potassium tolerant catalysts. Addition of alumino silicates, often in the form of coal fly ash, is an industrially proven method of removing K aerosols from flue gases. Tail-end placement of the SCR unit was also reported to result in acceptable catalyst stability; however, flue-gas reheating after the flue gas desulfurization is, at present, unavoidable due to the lack of sulfur and water tolerant low temperature catalysts. Coating the shaped catalysts with thin layers of, e.g., MgO or sepiolite reduces the K uptake by hindering the diffusion of K+ into the catalyst pore system. Intrinsically potassium tolerant catalysts typically contain a high number of acid sites. This can be achieved by, e.g., using zeolites as support, replacing WO3 with heteropoly acids, and by preparing highly loaded, high surface area, very active V2O5/TiO2 catalyst using a special sol-gel method.

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