scholarly journals Fischer-Tropsch Synthesis: The Characterization and Testing of Pt-Co/SiO2 Catalysts Prepared with Alternative Cobalt Precursors

Reactions ◽  
2021 ◽  
Vol 2 (2) ◽  
pp. 129-160
Author(s):  
Mohammad Mehrbod ◽  
Michela Martinelli ◽  
Caleb D. Watson ◽  
Donald C. Cronauer ◽  
A. Jeremy Kropf ◽  
...  
Keyword(s):  
Active Sites ◽  
Cobalt Chloride ◽  
Weak Interactions ◽  
Low Cost ◽  
Cobalt Acetate ◽  
Cobalt Nitrate ◽  
Strong Interactions ◽  
X Ray ◽  
Temperature Programmed ◽  
X Ray Absorption

Different low-cost cobalt precursors (acetate, chloride) and thermal treatments (air calcination/H2 reduction versus direct H2-activation) were investigated to alter the interaction between cobalt and silica. H2-activated catalysts prepared from cobalt chloride had large Co0 particles (XRD, chemisorption) formed by weak interactions between cobalt chloride and silica (temperature programmed reduction (TPR), TPR with mass spectrometry (TPR-MS), TPR with extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge spectroscopy (XANES) techniques) and retained Cl-blocked active sites, resulting in poor activity. In contrast, unpromoted Co/SiO2 catalysts derived from cobalt acetate had strong interactions between Co species and silica (TPR/TPR-MS, TPR-EXAFS/XANES); adding Pt increased the extent of the Co reduction. For these Pt-promoted catalysts, the reduction of uncalcined catalysts was faster, resulting in larger Co0 clusters (19.5 nm) in comparison with the air-calcined/H2-activated catalyst (7.8 nm). Both catalysts had CO conversions 25% higher than that of the Pt-promoted catalyst prepared in the traditional manner (air calcination/H2 reduction using cobalt nitrate) and three times higher than that of the traditional unpromoted Co/silica catalyst. The retention of residual cobalt carbide (observed in XANES) from cobalt acetate decomposition impacted performance, resulting in a higher C1–C4 selectivity (32.2% for air-calcined and 38.7% for uncalcined) than that of traditional catalysts (17.5–18.6%). The residual carbide also lowered the α-value and olefin/paraffin ratio. Future work will focus on improving selectivity through oxidation–reduction cycles.

scholarly journals Low Temperature Water-Gas Shift: Enhancing Stability through Optimizing Rb Loading on Pt/ZrO2

Catalysts ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 210
Author(s):  
Caleb Daniel Watson ◽  
Michela Martinelli ◽  
Donald Charles Cronauer ◽  
A. Jeremy Kropf ◽  
Gary Jacobs
Keyword(s):  
Low Temperature ◽  
Hydrogen Transfer ◽  
Water Gas Shift ◽  
Significant Shift ◽  
Catalyst Activation ◽  
X Ray ◽  
Temperature Programmed ◽  
Water Gas ◽  
X Ray Absorption ◽  
Temperature Water

Recent studies have shown that appropriate levels of alkali promotion can significantly improve the rate of low-temperature water gas shift (LT-WGS) on a range of catalysts. At sufficient loadings, the alkali metal can weaken the formate C–H bond and promote formate dehydrogenation, which is the proposed rate determining step in the formate associative mechanism. In a continuation of these studies, the effect of Rb promotion on Pt/ZrO2 is examined herein. Pt/ZrO2 catalysts were prepared with several different Rb loadings and characterized using temperature programmed reduction mass spectrometry (TPR-MS), temperature programmed desorption (TPD), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), an X-ray absorption near edge spectroscopy (XANES) difference procedure, extended X-ray absorption fine structure spectroscopy (EXAFS) fitting, TPR-EXAFS/XANES, and reactor testing. At loadings of 2.79% Rb or higher, a significant shift was seen in the formate ν(CH) band. The results showed that a Rb loading of 4.65%, significantly improves the rate of formate decomposition in the presence of steam via weakening the formate C–H bond. However, excessive rubidium loading led to the increase in stability of a second intermediate, carbonate and inhibited hydrogen transfer reactions on Pt through surface blocking and accelerated agglomeration during catalyst activation. Optimal catalytic performance was achieved with loadings in the range of 0.55–0.93% Rb, where the catalyst maintained high activity and exhibited higher stability in comparison with the unpromoted catalyst.

scholarly journals In-Exchanged CHA Zeolites for Selective Dehydrogenation of Ethane: Characterization and Effect of Zeolite Framework Type

Catalysts ◽  
2020 ◽  
Vol 10 (7) ◽  
pp. 807
Author(s):  
Zen Maeno ◽  
Xiaopeng Wu ◽  
Shunsaku Yasumura ◽  
Takashi Toyao ◽  
Yasuharu Kanda ◽  
...  
Keyword(s):  
Active Sites ◽  
Temperature Programmed Desorption ◽  
X Ray Diffraction ◽  
Zeolite Framework ◽  
X Ray ◽  
Catalytic Activities ◽  
Ethane Dehydrogenation ◽  
Temperature Programmed

In this study, the characterization of In-exchanged CHA zeolite (In-CHA (SiO2/Al2O3 = 22.3)) was conducted by in-situ X-ray diffraction (XRD) and ammonia temperature-programmed desorption (NH3-TPD). We also prepared other In-exchanged zeolites with different zeolite structures (In-MFI (SiO2/Al2O3 = 22.3), In-MOR (SiO2/Al2O3 = 20), and In-BEA (SiO2/Al2O3 = 25)) and different SiO2/Al2O3 ratios (In-CHA(Al-rich) (SiO2/Al2O3 = 13.7)). Their catalytic activities in nonoxidative ethane dehydrogenation were compared. Among the tested catalysts, In-CHA(Al-rich) provided the highest conversion. From kinetic experiments and in-situ Fourier transform infrared (FTIR) spectroscopy, [InH2]+ ions are formed regardless of SiO2/Al2O3 ratio, serving as the active sites.

scholarly journals Properties of Iron-Modified-by-Silver Supported on Mordenite as Catalysts for NOx Reduction

Catalysts ◽  
2020 ◽  
Vol 10 (10) ◽  
pp. 1156 ◽  
Author(s):  
Perla Sánchez-López ◽  
Yulia Kotolevich ◽  
Evgeny Khramov ◽  
Ramesh Kumar Chowdari ◽  
Miguel Angel Estrada ◽  
...  
Keyword(s):  
Ion Exchange ◽  
Bimetallic Catalysts ◽  
Active Sites ◽  
Nox Reduction ◽  
The State ◽  
Edge Structure ◽  
X Ray ◽  
Disordered Phase ◽  
Activity Test ◽  
X Ray Absorption

A series of mono and bimetallic catalysts based on a Fe-Ag mixture deposited on mordenite was prepared by ion-exchange and evaluated in the catalytic activity test of the de-NOx reaction in the presence of CO/C3H6. The activity results showed that the most active samples were the Fe-containing ones, and at high temperatures, a co-promoter effect of Ag on the activity of Fe catalysts was also observed. The influence of the order of cation deposition on catalysts formation and their physicochemical properties was studied by FTIR (Fourier Transform Infrared Spectroscopy) of adsorbed NO, XANES (X-ray Absorption Near-Edge Structure), and EXAFS (Extended X-ray Absorption Fine Structure) and discussed in terms of the state of iron. Results of Fe K-edge XANES oscillations showed that, in FeMOR catalysts, iron was present in a disordered state as Fe3+ and Fe2+. In FeAgMOR, the prevailing species was Fe3+, while in the AgFeMOR catalyst, the state of iron was intermediate or mixed between FeMOR and FeAgMOR. The Fe K-edge EXAFS results were characteristic of a disordered phase, the first coordination sphere being asymmetric with two different Fe-O distances. In FeAgMOR and AgFeMOR, coordination of Fe-O was similar to Fe2O3 with a few amount of Fe2+ species. We may conclude that, in the bimetallic FeAgMOR and AgFeMOR samples, a certain amount of tetrahedral Al3+ ions in the mordenite framework is replaced by Fe3+ ions, confirming the previous reports that these species are active sites for the de-NOx reaction. Based on the thermodynamic analysis and experimental data, also, it was confirmed that the order of deposition of the components influenced the mechanism of active sites’ formation during the two steps ion-exchange synthesis.

scholarly journals Experimental Investigations of the Interaction of SO2 with MgO

1999 ◽  
Vol 590 ◽  
Author(s):  
Andrea Freitag ◽  
J. A. Rodriguez ◽  
J. Z. Larese
Keyword(s):  
High Resolution ◽  
Film Thickness ◽  
Room Temperature ◽  
Temperature Programmed Desorption ◽  
Experimental Investigations ◽  
X Ray Diffraction ◽  
High Quality ◽  
X Ray ◽  
Temperature Programmed ◽  
X Ray Absorption

ABSTRACTHigh resolution adsorption isotherms, temperature programmed desorption (TPD), x-ray diffraction (XRD) and x-ray absorption near edge spectroscopy (XANES) methods were used to investigate the interaction of SO2 with high quality MgO powders. The results of these investigations indicate that when SO2 is deposited on MgO in monolayer quantities at temperatures near 100K both SO3 and SO4 species form that are not removed by simply pumping on the pre-dosed samples at room temperature. TPD and XANES studies indicate that heating of pre-dosed MgO samples to temperatures above 350 °C is required for full removal of the SO3/SO4 species. XANES measurements made as a function of film thickness indicate for coverages near monolayer completion that the SO4 species form first.

scholarly journals X-ray absorption measurements on an ultrasonic spray aerosol

2011 ◽  
Vol 19 (1) ◽  
pp. 126-128 ◽  
Author(s):  
R. Schlaf ◽  
B. Höpfner ◽  
J. Figueroa ◽  
E. Tridas ◽  
E. Welter ◽  
...  
Keyword(s):  
Spray Deposition ◽  
Mass Density ◽  
Low Cost ◽  
Buffer Layers ◽  
Solution Flow ◽  
X Ray ◽  
Simple Implementation ◽  
Good Signal ◽  
X Ray Absorption ◽  
Absorption Measurements

Spray deposition of thin films and coatings is a widely used manufacturing process owing to its low cost, versatility and simple implementation. The objective of the presented experiments was to investigate whether X-ray absorption measurements on solutes carried by aerosols are possible, and what count rates can be achieved depending on solution flow through and the resulting mass density in the interrogation volume. The investigated prototypical spray aerosol was InCl3dissolved in water or ethanol dispersedviaan ultrasonic nebulizer. InCl3spray is essential for the ion layer gas reaction process used for the deposition of In2S3buffer layers for highly efficient chalcopyrite solar cells. The discussed experiments demonstrate that measurements are possible, but that the achievement of good signal-to-noise ratios requires extended sampling times and concentrated solutions.

scholarly journals A Cobalt-Iron Double-Atom Catalyst for the Oxygen Evolution Reaction

2019 ◽  
Author(s):  
Lichen Bai ◽  
Chia-Shuo Hsu ◽  
Duncan Alexander ◽  
Hao Ming Chen ◽  
Xile Hu
Keyword(s):  
Oxygen Evolution ◽  
Active Site ◽  
Oxygen Evolution Reaction ◽  
Active Sites ◽  
Single Atom ◽  
X Ray ◽  
Highly Active ◽  
Cobalt Iron ◽  
X Ray Absorption

Single atom catalysts exhibit well-defined active sites and potentially maximum atomic efficiency. However, they are unsuitable for reactions that benefit from bimetallic promotion such as the oxygen evolution reaction (OER) in alkaline medium. Here we show that a single atom Co precatalyst can be in-situ transformed into a Co-Fe double atom catalyst for OER. This catalyst exhibits one of the highest turnover frequencies among metal oxides. Electrochemical, microscopic, and spectroscopic data including those from operando X-ray absorption spectroscopy, reveal a dimeric Co-Fe moiety as the active site of the catalyst. This work demonstrates double-atom catalysis as a promising approach for the developed of defined and highly active OER catalysts.

scholarly journals In situ X-ray absorption spectroscopic studies of TiO2 photocatalytic active sites for degradation of trace CHCl3 in drinking water

2021 ◽  
Vol 28 (6) ◽  
Author(s):  
T.-L. Hsiung ◽  
L.-W. Wei ◽  
H.-L. Huang ◽  
H. Paul Wang
Keyword(s):  
Drinking Water ◽  
Photocatalytic Degradation ◽  
Active Sites ◽  
Spectroscopic Studies ◽  
Band Gap Energy ◽  
Disinfection Byproducts ◽  
Edge Structure ◽  
X Ray ◽  
X Ray Absorption

Toxic disinfection byproducts such as trihalomethanes (e.g. CHCl3) are often found after chlorination of drinking water. It has been found that photocatalytic degradation of trace CHCl3 in drinking water generally lacks an expected relationship with the crystalline phase, band-gap energy or the particle sizes of the TiO2-based photocatalysts used such as nano TiO2 on SBA-15 (Santa Barbara amorphous-15), TiO2 clusters (TiO2–SiO2) and atomic dispersed Ti [Ti-MCM-41 (Mobil Composition of Matter)]. To engineer capable TiO2 photocatalysts, a better understanding of their photoactive sites is of great importance and interest. Using in situ X-ray absorption near-edge structure (XANES) spectroscopy, the A1 (4969 eV), A2 (4971 eV) and A3 (4972 eV) sites in TiO2 can be distinguished as four-, five- and six- coordinated Ti species, respectively. Notably, the A2 Ti sites that are the main photocatalytic species of TiO2 are shown to be accountable for about 95% of the photocatalytic degradation of trace CHCl3 in drinking water (7.2 p.p.m. CHCl3 gTiO2 −1 h−1). This work reveals that the A2 Ti species of a TiO2-based photocatalyst are mainly responsible for the photocatalytic reactivity, especially in photocatalytic degradation of CHCl3 in drinking water.

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

1992 ◽  
Vol 57 (4) ◽  
pp. 817-825 ◽  
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.

scholarly journals Atomically dispersed Fe3+ sites catalyze efficient CO2 electroreduction to CO

Science ◽  
2019 ◽  
Vol 364 (6445) ◽  
pp. 1091-1094 ◽  
Author(s):  
Jun Gu ◽  
Chia-Shuo Hsu ◽  
Lichen Bai ◽  
Hao Ming Chen ◽  
Xile Hu
Keyword(s):  
Active Sites ◽  
Carbon Support ◽  
Single Atom ◽  
Electronic Coupling ◽  
X Ray ◽  
Precious Metal Catalysts ◽  
Co2 Electroreduction ◽  
X Ray Absorption ◽  
Partial Current ◽  
Modest Activity

Currently, the most active electrocatalysts for the conversion of CO2 to CO are gold-based nanomaterials, whereas non–precious metal catalysts have shown low to modest activity. Here, we report a catalyst of dispersed single-atom iron sites that produces CO at an overpotential as low as 80 millivolts. Partial current density reaches 94 milliamperes per square centimeter at an overpotential of 340 millivolts. Operando x-ray absorption spectroscopy revealed the active sites to be discrete Fe3+ ions, coordinated to pyrrolic nitrogen (N) atoms of the N-doped carbon support, that maintain their +3 oxidation state during electrocatalysis, probably through electronic coupling to the conductive carbon support. Electrochemical data suggest that the Fe3+ sites derive their superior activity from faster CO2 adsorption and weaker CO absorption than that of conventional Fe2+ sites.

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