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

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.

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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.

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

Catalysts ◽

10.3390/catal9121018 ◽

2019 ◽

Vol 9 (12) ◽

pp. 1018

Author(s):

Naveed Husnain ◽

Enlu Wang ◽

Shagufta Fareed ◽

Muhammad Tuoqeer Anwar

Keyword(s):

Photoelectron Spectroscopy ◽

Catalytic Reduction ◽

Acid Sites ◽

High Concentration ◽

X Ray ◽

Nh3 Scr ◽

Transmission Electron ◽

Temperature Programmed ◽

Diffuse Reflectance Infrared

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.

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Machine Learning Powered by Principal Component Descriptors as the Key for Sorted Structural Fit of XANES

Physical Chemistry Chemical Physics ◽

10.1039/d1cp01794b ◽

2021 ◽

Author(s):

Andrea Martini ◽

Alexander A. Guda ◽

Sergey A. Guda ◽

Aram L. Bugaev ◽

Olga V. Safonova ◽

...

Keyword(s):

Machine Learning ◽

Structural Analysis ◽

Synchrotron Radiation ◽

Free Electron Laser ◽

Principal Component ◽

Analytical Tool ◽

X Ray ◽

Radiation Sources ◽

X Ray Absorption

Modern synchrotron radiation sources and free electron laser made X-ray absorption spectroscopy (XAS) an analytical tool for the structural analysis of materials under in situ or operando conditions. Fourier approach...

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Insights into sulfur poisoning and regeneration of Cu-SSZ-13 catalysts: In situ Cu and S K-edge XAS studies

Catalysis Science & Technology ◽

10.1039/d1cy00975c ◽

2021 ◽

Author(s):

Vitaly Mesilov ◽

Sandra Dahlin ◽

Susanna Liljegren Bergman ◽

Peter Sams Hammershøi ◽

Shibo Xi ◽

...

Keyword(s):

Selective Catalytic Reduction ◽

Oxidation State ◽

Absorption Spectroscopy ◽

Catalytic Reduction ◽

Sulfur Poisoning ◽

X Ray ◽

Scr Catalysts ◽

X Ray Absorption

In situ Cu and S K-edge X-ray absorption spectroscopy (XAS) was used for the investigation of sulfur-poisoned and regenerated Cu-SSZ-13 selective catalytic reduction (SCR) catalysts. Sulfur in the oxidation state...

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Effect of Organic Assistant on the Performance of Ceria-Based Catalysts for the Selective Catalytic Reduction of NO with Ammonia

Catalysts ◽

10.3390/catal9040357 ◽

2019 ◽

Vol 9 (4) ◽

pp. 357 ◽

Cited By ~ 3

Author(s):

Huang ◽

Li ◽

Qiu ◽

Chen ◽

Cheng ◽

...

Keyword(s):

Selective Catalytic Reduction ◽

Ball Milling ◽

Catalytic Reduction ◽

Temperature Programmed Desorption ◽

Milling Process ◽

X Ray ◽

Ball Milling Process ◽

Nh3 Scr ◽

Temperature Programmed ◽

Catalytic Performances

In the present study, a series of CeO2/TiO2 catalysts were fabricated by dry ball milling method in the absence and presence of organic assistants, and their catalytic performances for the selective catalytic reduction (SCR) of NO by NH3 were investigated. It was found that the addition of organic assistants in the ball milling process and the calcining ambience exerted a significant influence on the catalytic performances of CeO2/TiO2 catalysts. The nitrogen sorption isotherm measurement (BET), powder X-ray diffraction (XRD), Raman spectra, high-resolution transmission electron microscopy (HR-TEM), hydrogen temperature-programmed reduction (H2-TPR), ammonia temperature-programmed desorption (NH3-TPD), sulfur dioxide temperature-programmed desorption (SO2-TPD), thermogravimetric analysis (TG), Fourier transform infrared (FT-IR) and X-ray photoelectron spectra (XPS) characterizations showed that the introduction of citric acid in the ball milling process could significantly change the decomposition process of the precursor mixture, which can lead to improved dispersion and reducibility of cerium species, surface acidity as well as the surface microstructure, all which were responsible for the high low temperature activity of CeTi-C-N in an NH3-SCR reaction. In contrast, the addition of sucrose in the milling process showed an inhibitory effect on the catalytic performance of CeO2/TiO2 catalyst in an NH3-SCR reaction, possibly due to the decrease of the crystallinity of the TiO2 support and the carbon residue covering the active sites.

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Reducibility of Rhenium in Pt-Re/Al2O3 Reforming Catalysts: A Temperature Programmed Reduction-X-Ray-Absorption Near-Edge Structure Study

Journal of Catalysis ◽

10.1006/jcat.1995.1164 ◽

1995 ◽

Vol 154 (2) ◽

pp. 222-229 ◽

Cited By ~ 11

Author(s):

C.G. Michel ◽

W.E. Bambrick ◽

R.H. Ebel ◽

G. Larsen ◽

G.L. Haller

Keyword(s):

Structure Study ◽

Temperature Programmed Reduction ◽

Edge Structure ◽

X Ray ◽

Reforming Catalysts ◽

Temperature Programmed ◽

X Ray Absorption

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Formation of Reactive Clusters in Pd-Y Zeolite by Reduction-Reoxidation Treatment

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19920817 ◽

1992 ◽

Vol 57 (4) ◽

pp. 817-825 ◽

Cited By ~ 2

Author(s):

Hiroshige Matsumoto ◽

Shuji Tanabe

Keyword(s):

Fine Structure ◽

Room Temperature ◽

Reactive Species ◽

Temperature Programmed Reduction ◽

Y Zeolite ◽

X Ray ◽

Absorption Fine ◽

Temperature Programmed ◽

X Ray Absorption

Preparation of a finely dispersed Pd-Y zeolite has been investigated by temperature-programmed reduction (TPR) and extended X-ray absorption fine structure (EXAFS) techniques. Upon the treatment by a sequence of calcination, reduction, and reoxidation, the original Pd(NH3)42+ ions in the zeolite transformed to reactive species, which were reduced with hydrogen at room temperature and characterized as small PdO clusters of about 25 Pd atoms.

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Selective Catalytic Reduction of NO with NH3 over Ce-W-Ti Oxide Catalysts Prepared by Solvent Combustion Method

Applied Sciences ◽

10.3390/app8122430 ◽

2018 ◽

Vol 8 (12) ◽

pp. 2430 ◽

Cited By ~ 1

Author(s):

Xinbo Zhu ◽

Yaolin Wang ◽

Yu Huang ◽

Yuxiang Cai

Keyword(s):

Selective Catalytic Reduction ◽

Catalytic Reduction ◽

Space Velocity ◽

Combustion Method ◽

Catalytic Performance ◽

Solution Combustion ◽

X Ray ◽

Nh3 Scr ◽

Scr Of No ◽

Temperature Programmed

In this work, a series of Ce-W-Ti catalysts were synthesized using a solution combustion method for the selective catalytic reduction (SCR) of NO with NH3 at low temperatures. The reaction performance of NH3-SCR of NO was significantly improved over the Ce-W-Ti catalysts compared to Ce0.4Ti and W0.4Ti catalysts, while Ce0.2W0.2Ti showed the best activity among all the samples. The Ce0.2W0.2Ti catalyst exhibited over 90% removal of NO and 100% N2 selectivity in the temperature range of 250–400 °C at a gas hourly space velocity (GHSV) of 120,000 mL·g−1·h−1. The Ce-W-Ti catalysts were characterized using N2 adsorption-desorption, X-ray diffraction, X-ray photoelectron spectrometry and temperature programmed desorption of NH3 to establish the structure-activity relationships of the Ce-W-Ti catalysts. The excellent catalytic performance of the Ce0.2W0.2Ti catalyst could be associated with the larger specific surface area, highly dispersed Ce and W species, increased amount of surface adsorbed oxygen (Oads) and enhanced total acidity on the catalyst surfaces.

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Spectral Decomposition of X-ray Absorption Spectroscopy Datasets: Methods and Applications

Crystals ◽

10.3390/cryst10080664 ◽

2020 ◽

Vol 10 (8) ◽

pp. 664 ◽

Cited By ~ 1

Author(s):

Andrea Martini ◽

Elisa Borfecchia

Keyword(s):

Absorption Spectroscopy ◽

Multivariate Curve Resolution ◽

Beam Position ◽

X Ray ◽

External Variables ◽

Spectral Profiles ◽

X Ray Absorption ◽

Further Development ◽

Selection Of

X-ray absorption spectroscopy (XAS) today represents a widespread and powerful technique, able to monitor complex systems under in situ and operando conditions, while external variables, such us sampling time, sample temperature or even beam position over the analysed sample, are varied. X-ray absorption spectroscopy is an element-selective but bulk-averaging technique. Each measured XAS spectrum can be seen as an average signal arising from all the absorber-containing species/configurations present in the sample under study. The acquired XAS data are thus represented by a spectroscopic mixture composed of superimposed spectral profiles associated to well-defined components, characterised by concentration values evolving in the course of the experiment. The decomposition of an experimental XAS dataset in a set of pure spectral and concentration values is a typical example of an inverse problem and it goes, usually, under the name of multivariate curve resolution (MCR). In the present work, we present an overview on the major techniques developed to realize the MCR decomposition together with a selection of related results, with an emphasis on applications in catalysis. Therein, we will highlight the great potential of these methods which are imposing as an essential tool for quantitative analysis of large XAS datasets as well as the directions for further development in synergy with the continuous instrumental progresses at synchrotron sources.

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