Comparision on the Low-Temperature NH3-SCR Performance of γ-Fe2O3 Catalysts Prepared by Two Different Methods

Maghemite (γ-Fe2O3) catalysts were prepared by two different methods, and their activities and selectivities for selective catalytic reduction of NO with NH3 were investigated. The methods of X-ray powder diffraction (XRD), Brunauer–Emmett–Teller (BET), X-ray photoelectron spectroscopy (XPS), hydrogen temperature-programmed reduction (H2-TPR), ammonia temperature-programmed desorption (NH3-TPD), transmission electron microscopy (TEM), Energy-dispersive X-ray spectroscopy (EDS), and in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS) were used to characterize the catalysts. The resulted demonstrated that the γ-Fe2O3 nanoparticles prepared by the facile method (γ-Fe2O3–FM) not only exhibited better NH3-SCR activity and selectivity than the catalyst prepared by the coprecipitation method but also showed improved SO2 tolerance. This superior NH3-SCR performance was credited to the existence of the larger surface area, better pore structure, a high concentration of lattice oxygen and surface-adsorbed oxygen, good reducibility, a lot of acid sites, lower activation energy, adsorption of the reactants, and the existence of unstable nitrates on the surface of the γ-Fe2O3–FM.

Download Full-text

Promoting Effect of Mn on In Situ Synthesized Cu-SSZ-13 for NH3-SCR

Catalysts ◽

10.3390/catal10121375 ◽

2020 ◽

Vol 10 (12) ◽

pp. 1375

Author(s):

Jinpeng Du ◽

Jingyi Wang ◽

Xiaoyan Shi ◽

Yulong Shan ◽

Yan Zhang ◽

...

Keyword(s):

Low Temperature ◽

Active Sites ◽

Catalytic Reduction ◽

Acid Sites ◽

Promoting Effect ◽

Nh3 Scr ◽

Temperature Programmed ◽

Diffuse Reflectance Infrared ◽

Redox Ability

The effect of Mn impregnation on the NH3-SCR (selective catalytic reduction of NOx by NH3) activity of in situ synthesized Cu-SSZ-13 was investigated in this work. It was found that Mn addition could efficiently improve the low-temperature activity of Cu-SSZ-13. The optimal amount of Mn was 5 wt.%, and NOx conversion was improved by more than 20% over a temperature range of 120 °C to 150 °C. SEM (scanning electron microscopy), XRD (X-ray diffraction), N2 adsorption-desorption, H2-TPR (temperature programmed reduction of H2), NH3-TPD (temperature programmed desorption of NH3) and in situ DRIFTS (diffuse reflectance infrared Fourier transform spectroscopy) experiments were conducted to investigate the changes in the zeolite structure, active sites, acid sites and reaction mechanism. The impregnated MnOx species caused a decline in the crystallinity of Cu-SSZ-13 but markedly improved the redox ability. Nitrate and nitrite species were observed in the Mn-modified Cu-SSZ-13, and the formation of these species was thought to cause the observed increase in low-temperature NH3-SCR activity. The results show that the addition of Mn is a promising method for promoting the low-temperature catalytic activity of Cu-SSZ-13.

Download Full-text

Hydrogenative Cyclization of Levulinic Acid to γ-Valerolactone with Methanol and Ni-Fe Bimetallic Catalysts

Catalysts ◽

10.3390/catal10091096 ◽

2020 ◽

Vol 10 (9) ◽

pp. 1096

Author(s):

Ligang Luo ◽

Xiao Han ◽

Qin Zeng

Keyword(s):

Photoelectron Spectroscopy ◽

Levulinic Acid ◽

Hydrogen Donor ◽

Effect Of Temperature ◽

X Ray ◽

Transmission Electron ◽

Ft Ir ◽

Temperature Programmed

A series of Ni-Fe/SBA-15 catalysts was prepared and tested for the catalytic hydrogenation of levulinic acid to γ-valerolactone, adopting methanol as the only hydrogen donor, and investigating the synergism between Fe and Ni, both supported on SBA-15, towards this reaction. The characterization of the synthesized catalysts was carried out by XRD (X-ray powder diffraction), TEM (transmission electron microscopy), H2-TPD (hydrogen temperature-programmed desorption), XPS (X-ray photoelectron spectroscopy), and in situ FT-IR (Fourier transform–infrared spectroscopy) techniques. H2-TPD and XPS results have shown that electron transfer occurs from Fe to Ni, which is helpful both for the activation of the C=O bond and for the dissociative activation of H2 molecules, also in agreement with the results of the in situ FT-IR spectroscopy. The effect of temperature and reaction time on γ-valerolactone production was also investigated, identifying the best reaction conditions at 200 °C and 180 min, allowing for the complete conversion of levulinic acid and the complete selectivity to γ-valerolactone. Moreover, methanol was identified as an efficient hydrogen donor, if used in combination with the Ni-Fe/SBA-15 catalyst. The obtained results are promising, especially if compared with those obtained with the traditional and more expensive molecular hydrogen and noble-based catalysts.

Download Full-text

Nanosized V-Ce Oxides Supported on TiO2 as a Superior Catalyst for the Selective Catalytic Reduction of NO

Catalysts ◽

10.3390/catal10020202 ◽

2020 ◽

Vol 10 (2) ◽

pp. 202

Author(s):

Long Lu ◽

Xueman Wang ◽

Chunhua Hu ◽

Ying Liu ◽

Xiongbo Chen ◽

...

Keyword(s):

Low Temperature ◽

Selective Catalytic Reduction ◽

Photoelectron Spectroscopy ◽

Catalytic Reduction ◽

X Ray Diffraction ◽

X Ray ◽

Transmission Electron ◽

Redox Capacity ◽

Scr Of No ◽

Temperature Programmed

Nanosized V-Ce oxides supported on TiO2 (VCT) were prepared and utilized in the low-temperature selective catalytic reduction (SCR) of NO with NH3. Compared with the other V-Ce oxides-based catalysts supported on Al2O3, ZrO2, and ZSM-5, VCT showed the best SCR activity in a low-temperature range. The NOx conversion of 90% could be achieved at 220 °C. Characterizations including X-ray diffraction (XRD), scanning election micrograph (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), temperature-programmed desorption with NH3 (NH3-TPD), and temperature-programmed reduction with H2 (H2-TPR) showed that V1.05Ce1/TiO2 exhibited a good dispersion of V2O5, enrichment of surface Ce3+ and chemical-absorbed oxygen, and excellent redox capacity and acidity, which resulted in the best SCR performance at low temperature.

Download Full-text

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

Catalysts ◽

10.3390/catal9010090 ◽

2019 ◽

Vol 9 (1) ◽

pp. 90 ◽

Cited By ~ 10

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).

Download Full-text

Modification of V2O5-WO3/TiO2 Catalyst by Loading of MnOx for Enhanced Low-Temperature NH3-SCR Performance

Nanomaterials ◽

10.3390/nano10101900 ◽

2020 ◽

Vol 10 (10) ◽

pp. 1900

Author(s):

Xianlong Zhang ◽

Qinchao Diao ◽

Xiaorui Hu ◽

Xueping Wu ◽

Kesong Xiao ◽

...

Keyword(s):

Manganese Oxides ◽

Catalytic Reduction ◽

In Situ Growth ◽

X Ray Diffraction ◽

Scr Catalyst ◽

X Ray ◽

Nh3 Scr ◽

Growth Method ◽

Temperature Programmed

V2O5-WO3/TiO2 as a commercial selective catalytic reduction (SCR) catalyst usually used at middle-high temperatures was modified by loading of MnOx for the purpose of enhancing its performance at lower temperatures. Manganese oxides were loaded onto V-W/Ti monolith by the methods of impregnation (I), precipitation (P), and in-situ growth (S), respectively. SCR activity of each modified catalyst was investigated at temperatures in the range of 100–340 °C. Catalysts were characterized by specific surface area and pore size determination (BET), X-ray diffraction (XRD), temperature programmed reduction (TPR), etc. Results show that the loading of MnOx remarkably enhanced the SCR activity at a temperature lower than 280 °C. The catalyst prepared by the in-situ growth method was found to be most active for SCR.

Download Full-text

Effect of Ce-modified Fe/ZSM-5 zeolite for selective catalytic reduction of NOx by ammonia

E3S Web of Conferences ◽

10.1051/e3sconf/202021803032 ◽

2020 ◽

Vol 218 ◽

pp. 03032

Author(s):

Chenxi Li ◽

Fanwei Meng ◽

Qing Ye

Keyword(s):

Selective Catalytic Reduction ◽

Photoelectron Spectroscopy ◽

Catalytic Reduction ◽

Catalytic Performance ◽

Acid Sites ◽

Impregnation Method ◽

Adsorption Ability ◽

In Situ Drifts ◽

X Ray

A series of xCe-Fe/ZSM-5 (x = 0, 0.25, 0.5 wt%) samples were prepared by the impregnation method, and the catalytic activity was evaluated by the selective catalytic reduction of NOx with ammonia (NH3-SCR). The physicochemical properties of prepared samples were characterized by various techniques such as X-ray diffraction (XRD), Brunner-Emmet-Teller (BET) measurement, hydrogen temperatureprogrammed reduction (H2-TPR), X-ray photoelectron spectroscopy (XPS), ammonia temperatureprogrammed desorption (NH3-TPD) and in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS). XRD and BET results demonstrated that Ce and Fe species were uniform dispersed on the surface of the ZSM-5 zeolite and the micropore structure of ZSM-5 was still maintained. H2-TPR analysis indicated that the doping of Ce created more isolated Ce4+ and Fe3+ on the surface of catalysts, and the abundant Ce4+ and Fe3+ could enhance the reduction ability of catalysts. XPS analysis suggested that the doping of Ce could generate more oxygen vacancies, thereby increasing the number of chemisorption oxygen. According to the in-situ DRIFTS and NH3-TPD results, Ce species provided more acidic sites, which is beneficial to the NH3 adsorption ability of ZSM-5 zeolite. Additionally, the abundant chemisorption oxygen, medium and strong Brønsted acid sites, excellent NH3 adsorption ability and outstanding reduction property are beneficial to the NH3-SCR reaction. Among all prepared samples, the 0.25Ce-Fe/ZSM-5 sample possessed the widest reaction temperature window and the best catalytic performance (NO conversion over 98% at 350-450 °C), which was associated with the abundant acid sites and remarkable adsorption ability of NH3, outstanding redox ability and abundant chemisorption oxygen after the doping of Ce.

Download Full-text

Precursor Effect on Mn-Fe-Ce/TiO2 Catalysts for Selective Catalytic Reduction of NO with NH3 at Low Temperatures

Catalysts ◽

10.3390/catal11020259 ◽

2021 ◽

Vol 11 (2) ◽

pp. 259

Author(s):

Siva Sankar Reddy Putluru ◽

Leonhard Schill ◽

Anker Degn Jensen ◽

Bernard Siret ◽

Frank Tabaries ◽

...

Keyword(s):

Low Temperature ◽

Selective Catalytic Reduction ◽

Photoelectron Spectroscopy ◽

Catalytic Reduction ◽

Reduction Of No ◽

X Ray ◽

Nh3 Scr ◽

Fast Scr ◽

Oxide Phases ◽

Temperature Programmed

Preparation of Mn/TiO2, Mn-Fe/TiO2, and Mn-Fe-Ce/TiO2 by the deposition-precipitation (DP) method can afford very active catalysts for low-temperature NH3-SCR (selective catalytic reduction of NO with NH3). The effect of precursor choice (nitrate vs. acetate) of Mn, Fe, and Ce on the physiochemical properties including thermal stability and the resulting SCR activity were investigated. The resulting materials were characterized by N2-Physisorption, XRD (Powder X-ray diffraction), XPS (X-ray photoelectron spectroscopy), H2-TPR (temperature-programmed reduction with hydrogen), and the oxidation of NO to NO2 measured at 300 °C. Among all the prepared catalysts 5MnAce/Ti, 25Mn0.75AceFe0.25Nit/Ti, and 25Mn0.75AceFe0.20NitCe0.05Ace/Ti showed superior SCR activity at low temperature. The superior activity of the latter two materials is likely attributable to the presence of amorphous active metal oxide phases (manganese-, iron- and cerium-oxide) and the ease of the reduction of metal oxides on TiO2. Enhanced ability to convert NO to NO2, which can promote fast-SCR like pathways, could be another reason. Cerium was found to stabilize amorphous manganese oxide phases when exposed to high temperatures.

Download Full-text

Preparation of Quasi-MIL-101(Cr) Loaded Ceria Catalysts for the Selective Catalytic Reduction of NOx at Low Temperature

Catalysts ◽

10.3390/catal10010140 ◽

2020 ◽

Vol 10 (1) ◽

pp. 140 ◽

Cited By ~ 1

Author(s):

Min Lu ◽

Haili Hou ◽

Chuanying Wei ◽

Xiaohui Guan ◽

Wei Wei ◽

...

Keyword(s):

Low Temperature ◽

Selective Catalytic Reduction ◽

Photoelectron Spectroscopy ◽

Catalytic Reduction ◽

Great Influence ◽

X Ray ◽

Nh3 Scr ◽

Transmission Electron ◽

Ir Transmission ◽

Ceria Catalysts

At present, the development of novel catalysts with high activity Selective Catalytic Reduction (SCR) reaction at the low temperature is still a challenge. In this work, the authors prepare CeO2/quasi-MIL-101 catalysts with various amounts of deposited ceria by a double-solvent method, which are characterized by X-ray diffraction (XRD), Fourier Transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and so on. The results show that the increase of Ce content has a great influence on the catalytic property of the catalyst. The introduction of Ce can promote the conversion between Cr3+ and Cr5+ and increase the proportion of lattice oxygen, which improves the activity of the catalyst. However, the catalyst will be peroxidized when the content of Ce is too high, resulting in the decline of the catalytic activity. This experiment indicates that CeO2/quasi-MIL-101 plays a significant role in the NH3-SCR process at the low temperature when the loading of Ce is 0.5%. This work has proved the potential of this kind of material in NH3-SCR process at the low temperature, providing help for subsequent studies.

Download Full-text

In situ X-ray absorption study of Cu species in Cu-CHA catalysts for NH3-SCR during temperature-programmed reduction in NO/NH3

Research on Chemical Intermediates ◽

10.1007/s11164-020-04350-1 ◽

2021 ◽

Author(s):

Chiara Negri ◽

Elisa Borfecchia ◽

Andrea Martini ◽

Gabriele Deplano ◽

Kirill A. Lomachenko ◽

...

Keyword(s):

Catalytic Reduction ◽

Principal Component ◽

Multivariate Curve Resolution ◽

Temperature Programmed Reduction ◽

X Ray ◽

Nh3 Scr ◽

Pretreatment Conditions ◽

Temperature Programmed ◽

X Ray Absorption

AbstractAmmonia-mediated selective catalytic reduction (NH3-SCR) using Cu-exchanged chabazite zeolites as catalysts is one of the leading technologies for NOx removal from exhaust gases, with CuII/CuI redox cycles being the basis of the catalytic reaction. The amount of CuII ions reduced by NO/NH3 can be quantified by the consumption of NO during temperature-programmed reduction experiments (NO-TPR). In this article, we show the capabilities of in situ X-ray absorption near-edge spectroscopy (XANES), coupled with multivariate curve resolution (MCR) and principal component analysis (PCA) methods, in following CuII/CuI speciation during reduction in NO/NH3 after oxidation in NO/O2 at 50 °C on samples with different copper loading and pretreatment conditions. Our XANES results show that during the NO/NH3 ramp CuII ions are fully reduced to CuI in the 50–290 °C range. The number of species involved in the process, their XANES spectra and their concentration profiles as a function of the temperature were obtained by MCR and PCA. Mixed ligand ammonia solvated complexes [CuII(NH3)3(X)]+ (X = OH−/O− or NO3−) are present at the beginning of the experiment, and are transformed into mobile [CuI(NH3)2]+ complexes: these complexes lose an NH3 ligand and become framework-coordinated above 200 °C. In the process, multiple CuII/CuI reduction events are observed: the first one around 130 °C is identified with the reduction of [CuII(NH3)3(OH/O)]+ moieties, while the second one occurs around 220–240 °C and is associated with the reduction of the ammonia-solvated Cu-NO3− species. The nitrate concentration in the catalysts is found to be dependent on the zeolite Cu loading and on the applied pretreatment conditions. Ammonia solvation increases the number of CuII sites available for the formation of nitrates, as confirmed by infrared spectroscopy.

Download Full-text

Selective Catalytic Reduction of NOx with NH3 over Mn2O3 supported with different morphology of CeO2 Catalysts

10.22541/au.163452243.37004611/v1 ◽

2021 ◽

Author(s):

Shyam Rao ◽

VIVEK PATEL ◽

Sweta Sharma

Keyword(s):

Electron Microscopy ◽

Photoelectron Spectroscopy ◽

Catalytic Reduction ◽

Catalytic Performance ◽

X Ray Diffraction ◽

Wet Impregnation ◽

X Ray ◽

Nh3 Scr ◽

Transmission Electron ◽

Reduction Of Nox

Three different morphologies of CeO2 supports (NP, NC, and NR) were prepared by hydrothermal method and further Mn2O3 is impregnated on CeO2 supports using wet-impregnation methods, and their activity for NO reduction using NH3-SCR technique is analysed. The prepared catalysts and supports are further characterized through scanning electron microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), and transmission electron microscopy (TEM), and Brunauer–Emmett–Teller (BET). The catalytic performance of Mn2O3/CeO2-NP has shown the highest conversion (76.06 %) compared to the other two catalysts in the temperature range of 50 - 450°C.

Download Full-text