scholarly journals Fluorescence-detected XAS with sub-second time resolution reveals new details about the redox activity of Pt/CeO2 catalyst

2018 ◽  
Vol 25 (4) ◽  
pp. 989-997 ◽  
Author(s):  
Alexander A. Guda ◽  
Aram L. Bugaev ◽  
Rene Kopelent ◽  
Luca Braglia ◽  
Alexander V. Soldatov ◽  
...  
Keyword(s):  
Time Resolution ◽  
Flow Reactor ◽  
Plug Flow ◽  
Redox Activity ◽  
Time Resolved ◽  
X Ray ◽  
Gas Atmosphere ◽  
Ceria Support ◽  
X Ray Absorption ◽  
Selective Oxidation Catalysts

A setup for fluorescence-detected X-ray absorption spectroscopy (XAS) with sub-second time resolution has been developed. This technique allows chemical speciation of low-concentrated materials embedded in highly absorbing matrices, which cannot be studied using transmission XAS. Using this setup, the reactivity of 1.5 wt% Pt/CeO2 catalyst was studied with 100 ms resolution during periodic cycling in CO- and oxygen-containing atmospheres in a plug-flow reactor. Measurements were performed at the Pt L 3- and Ce L 3-edges. The reactivity of platinum and cerium demonstrated a strong correlation. The oxidation of the catalyst starts on the ceria support helping the oxidation of platinum nanoparticles. The new time-resolved XAS setup can be applied to various systems, capable of reproducible cycling between different states triggered by gas atmosphere, light, temperature, etc. It opens up new perspectives for mechanistic studies on automotive catalysts, selective oxidation catalysts and photocatalysts.

scholarly journals Time-Resolved X-ray Absorption Spectroscopy in (Photo)Electrochemistry

Surfaces ◽  
2018 ◽  
Vol 1 (1) ◽  
pp. 138-150 ◽  
Author(s):  
Martina Fracchia ◽  
Paolo Ghigna ◽  
Alberto Vertova ◽  
Sandra Rondinini ◽  
Alessandro Minguzzi
Keyword(s):  
Oxidation State ◽  
Absorption Spectroscopy ◽  
Time Resolution ◽  
Local Structure ◽  
Future Perspectives ◽  
Time Resolved ◽  
X Ray ◽  
Fixed Energy ◽  
Complete Survey ◽  
X Ray Absorption

This minireview aims at providing a complete survey concerning the use of X-ray absorption spectroscopy (XAS) for time-resolved studies of electrochemical and photoelectrochemical phenomena. We will see that time resolution can range from the femto-picosecond to the second (or more) scale and that this joins the valuable throughput typical of XAS, which allows for determining the oxidation state of the investigated element, together with its local structure. We will analyze four different techniques that use different approaches to exploit the in real time capabilities of XAS. These are quick-XAS, energy dispersive XAS, pump & probe XAS and fixed-energy X-ray absorption voltammetry. In the conclusions, we will analyze possible future perspectives for these techniques.

scholarly journals Fluorescence-detected quick-scanning X-ray absorption spectroscopy

2020 ◽  
Vol 27 (3) ◽  
pp. 681-688 ◽  
Author(s):  
Adam H. Clark ◽  
Patrick Steiger ◽  
Benjamin Bornmann ◽  
Stephan Hitz ◽  
Ronald Frahm ◽  
...  
Keyword(s):  
Absorption Spectroscopy ◽  
Time Resolution ◽  
The State ◽  
Complex Materials ◽  
Time Resolved ◽  
Temperature Oxidation ◽  
X Ray ◽  
Signal Collection ◽  
Transmission Measurements ◽  
X Ray Absorption

Time-resolved X-ray absorption spectroscopy (XAS) offers the possibility to monitor the state of materials during chemical reactions. While this technique has been established for transmission measurements for a number of years, XAS measurements in fluorescence mode are challenging because of limitations in signal collection as well as detectors. Nevertheless, measurements in fluorescence mode are often the only option to study complex materials containing heavy matrices or in samples where the element of interest is in low concentration. Here, it has been demonstrated that high-quality quick-scanning full extended X-ray absorption fine-structure data can be readily obtained with sub-second time resolution in fluorescence mode, even for highly diluted samples. It has also been demonstrated that in challenging samples, where transmission measurements are not feasible, quick fluorescence can yield significant insight in reaction kinetics. By studying the fast high-temperature oxidation of a reduced LaFe0.8Ni0.8O3 perovskite type, an example where the perovskite matrix elements prevent measurements in fluorescence, it is shown that it is now possible to follow the state of Ni in situ at a 3 s time resolution.

scholarly journals The Effect of Mg and Zn Dopants on Pt/Al2O3 for the Dehydrogenation of Perhydrodibenzyltoluene

Catalysts ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 490
Author(s):  
Rudaviro Garidzirai ◽  
Phillimon Modisha ◽  
Innocent Shuro ◽  
Jacobus Visagie ◽  
Pieter van Helden ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Inductively Coupled Plasma ◽  
Flow Reactor ◽  
Plug Flow ◽  
Optical Emission ◽  
Catalytic Performance ◽  
Emission Spectrometry ◽  
Hydrogen Yield ◽  
X Ray ◽  
Temperature Programmed

The effects of Mg and Zn dopants on the catalytic performance of Pt/Al2O3 catalyst were investigated for dehydrogenation of perhydrodibenzyltoluene (H18-DBT) as a liquid organic hydrogen carrier. Al2O3 supports were modified with Mg and Zn to produce Mg-Al2O3 and Zn-Al2O3 with a target loading of 3.8 wt.% for dopants. The modified supports were impregnated with chloroplatinic acid solution to produce the catalysts Pt/Al2O3, Pt/Mg-Al2O3 and Pt/Zn-Al2O3 of 0.5 wt.% Pt loading. Thereafter, the catalysts were characterised using inductively coupled plasma- optical emission spectrometry, scanning electron microscopy-energy dispersive X-ray spectroscopy, hydrogen temperature-programmed reduction, carbon-monoxide pulse chemisorption, ammonia temperature-programmed desorption, X-ray diffraction and transmission electron microscopy. The dehydrogenation experiments were performed using a horizontal plug flow reactor system and the catalyst time-on-stream was 22 h. Pt/Mg-Al2O3 showed the highest average hydrogen flowrate of 29 nL/h, while an average of 27 nL/h was obtained for both Pt/Al2O3 and Pt/Zn-Al2O3. This has resulted in a hydrogen yield of 80% for Pt/Mg-Al2O3, 71% for Pt/Zn-Al2O3 and 73% for Pt/Al2O3. In addition, the conversion of H18-DBT ranges from 99% to 92%, Pt 97–90% and 96–90% for Pt/Mg-Al2O3, Pt/Zn-Al2O3 and Pt/Al2O3, respectively. Following the latter catalyst order, the selectivity to dibenzyltoluene (H0-DBT) ranges from 78% to 57%, 75–51% and 71–45%. Therefore, Pt/Mg-Al2O3 showed improved catalytic performance towards dehydrogenation of H18-DBT.

scholarly journals A setup for ultrafast time-resolved x-ray absorption spectroscopy

2004 ◽  
Vol 75 (1) ◽  
pp. 24-30 ◽  
Author(s):  
Melanie Saes ◽  
Frank van Mourik ◽  
Wojciech Gawelda ◽  
Maik Kaiser ◽  
Majed Chergui ◽  
...  
Keyword(s):  
Absorption Spectroscopy ◽  
Time Resolved ◽  
X Ray ◽  
X Ray Absorption
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