Anna Zimina

Anna Zimina
Karlsruhe Institute of Technology | KIT · Institute for Catalysis Research and Technology (IKFT)

PhD

About

51
Publications
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795
Citations

Publications

Publications (51)
Article
The formation of octanuclear cobalt core has been studied in the Co complexes Na[Co8{O2CCH3}8(OCH3)16]NO3(1), Na[Co8{O2CC(CH3)3}8(OCH3)16]NO3(2), Na[Co8{O2CC(CH3)3}8 (OC2H5)16]NO3(3) by analysing the X-ray absorption spectra at the Co K-edge. Analysis of EXAFS confirmed octahedral coordination around the Co atoms. The presence of neighbouring Co at...
Article
Full-text available
The production of liquid hydrocarbons from syngas (CO and H 2 ) via the combined Fischer‐Tropsch (FT) synthesis and hydroprocessing (HP) is a promising strategy to provide valuable chemicals and fuels based on renewable feedstocks. High yields of liquid products are essential for industrial implementation since short‐chain side products like methan...
Article
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The first liquid-phase synthesis of high-quality, small-sized rare-earth metal nanoparticles (1-3 nm) - ranging from lanthanum as one of the largest (187 pm) to scandium as the smallest (161 pm) rare-earth metal - is shown. Size, oxidation state, and reactivity of the nanoparticles are examined (e.g., electron microscopy, electron spectroscopy, X-r...
Article
Zerovalent niobium, Nb(0), and tantalum, Ta(0), nanoparticles are prepared via a one-pot, liquid-phase synthesis. For this, NbCl5/TaCl5 are dissolved in pyridine and reduced by lithium pyridinyl. Deep black suspensions of very small, highly uniform nanoparticles are obtained with average diameters of 2.1 ± 0.4 nm (Nb(0)) and 1.9 ± 0.4 nm (Ta(0)). W...
Article
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Reactive but easy to handle: For the first time, rare-earth metals (La, Ce, Sm, Eu, Tm, Y, Sc) are obtained as high-quality nanoparticles (1–3 nm in size) in the liquid phase. They can be highly interesting as reactive starting materials to realize new rare-earth metal compounds and/or phase-pure rare-earth-metal-based materials. Abstract The firs...
Article
A modular high-temperature cell consisting of a plug-flow microreactor with a fixed catalyst bed and long heating zone has been established for operando x-ray absorption/fluorescence spectroscopic and diffraction studies. The functionality of the cell is demonstrated for two important areas: emission control using 2 wt. % Pd/Al2O3 acting as a three...
Article
Four Mo-based catalysts were prepared via three different synthesis techniques supported on SiO 2 and/or SBA-15. By means of complementary in situ characterization techniques, the carburization process and the final characteristics of these catalysts were investigated. Additionally, the four catalysts were evaluated for the activation of CO 2 in th...
Article
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V2O5−WO3/TiO2 (VWTi) catalysts are widely employed for selective catalytic reduction (SCR) of NOx. However, due to their poor thermal stability the application in diesel particulate filters (DPFs), i. e. 2‐way SCRonDPF is limited. In this study, the potential of Ce‐ and Fe‐doped VWTi systems for hydrocarbon and soot oxidation in addition to the SCR...
Article
Reduction and Carburization of Iron Oxides for Fischer-Tropsch Synthesis - Monia Nielsen, Asger Moss, Anton Simon Bjørnlund, Xi Liu, Axel Knop-Gericke Knop-Gericke, Alexander Yu. Klyushin, Jan-Dierk Grunwaldt, Thomas Sheppard, Dmitry E. Doronkin, Anna Zimina, Thomas Erik Lyck Smithuysen, Yakub Fam, Christian Danvad Damsgaard, Jakob Wagner, Thomas H...
Article
Thermoresistive catalytic combustion sensors based on noble metals are very stable and highly sensitive devices to monitor potentially explosive atmospheres. We studied and proved the high stability of rhodium oxide-based sensors under working conditions in different CH4/air mixtures (up to 3.5 vol.% methane) with the help of operando X-ray based c...
Article
Silver-catalyzed oxidation of 5-(hydroxymethyl)furfural (HMF) to 5-hydroxymethyl-2-furancarboxylic acid (HFCA) was investigated using Ag/ZrO2 and Ag/TiO2 catalysts. The reaction proceeded very selectively without formation of the dicarboxylic acid in the presence of air and NaOH as a base. In situ X-ray absorption spectroscopy (XAS) performed syste...
Article
The direct synthesis of hydrogen peroxide over TiO2-supported mono- and bimetallic Pd, PdSn, and PdIn nanoparticles (NPs) was performed in a continuous plug-flow reactor at 80 bar in ethanol with H2:O2 ratios varied from 10:1 to 1:10. At the same time the catalysts were monitored by operando X-ray absorption spectroscopy (XAS). The setup optimized...
Article
Pd-Pt/Al2O3 and Pd-Pt/CeO2-ZrO2-Y2O3-La2O3 methane oxidation catalysts were investigated under typical lean-burn gas engine conditions with respect to sulfur poisoning and during reactivation, particularly under the most efficient rich conditions. Sulfation of the noble metal and the support material led to pronounced catalyst deactivation. A prono...
Article
Full-text available
In order to reduce CO2 emissions, it is necessary to substitute fossil fuels with renewable energy using CO2 as carbon feedstock. An attractive route for synthetic fuel production is the Fe- or Co-catalysed Fischer-Tropsch process. A profound knowledge of the catalyst deactivation phenomena under industrial conditions is crucial for the process opt...
Article
The activation of iron oxide Fischer-Tropsch synthesis (FTS) catalysts was investigated during pretreatment: reduction in hydrogen followed by carburization in either CO or syngas mixture, or simultaneously reduction and carburization in syngas. A combination of different complementary in situ techniques was used to gain insight into the behavior o...
Article
A screening study of the catalytic performance of ternary alloy nanoparticles containing nickel, iron and gallium supported on silica for methanol synthesis from CO2 and H2 was performed. Catalysts were prepared by incipient wetness impregnation and subsequently reduced in H2 before catalytic testing. Ni2FeGa showed the best performance of the test...
Article
Two series of Pt/γ‐Al 2 O 3 catalysts for low temperature NH 3 oxidation were prepared using Pt(NO 3 ) 4 and H 2 PtCl 6 precursors. Using both precursors results in the formation of small Pt particles (d<1.5 nm), however, Cl‐containing Pt precursors give a higher fraction of highly dispersed Pt species. Such species show high stability against ther...
Article
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The catalytic activity of high-loaded Ni-based catalysts for beech wood fast-pyrolysis bio-oil hydrotreatment is compared to Ru/C. The influence of promoter, temperature, reaction time, and consecutive upgrading is investigated. The catalytic activity is addressed in terms of elemental composition, pH value, H2 consumption, and water content, while...
Article
Full-text available
Zink‐stabilisierte Palladiumkolloide mit einer Größe von ≈2 nm sind Schlüsselbausteine für bifunktionale Synthesegas‐zu‐Dimethylether‐Katalysatoren mit erhöhter Stabilität, Langlebigkeit und hoher Dimethyletherselektivität. Die Katalysatoren wurden mit einer Kombination von Hochdruck‐Operando‐Röntgenabsorptionsspektroskopie und DFT‐Rechnungen chara...
Article
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The single‐step syngas‐to‐dimethyl ether (STD) process entails economic and technical advantages over the current industrial two‐step process. Pd/ZnO‐based catalysts have recently emerged as interesting alternatives to currently used Cu/ZnO/Al₂O₃ catalysts, but the nature of the active site(s), the reaction mechanism and the role of Pd and ZnO in t...
Article
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Photocatalytic conversion of CO2 to solar fuels (CO, CH4) is considered an alternative approach for simultaneously mitigating the greenhouse effect and solving energy shortage. The efficient light harvesting and the thermochemical conversion has been a demanding quest in photocatalysis due to the relatively low solar energy utilization efficiency....
Article
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In order to increase their stability and tune-sensing characteristics, metal oxides are often surface-loaded with noble metals. Although a great deal of empirical work shows that surface-loading with noble metals drastically changes sensing characteristics, little information exists on the mechanism. Here, a systematic study of sensors based on rho...
Article
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Residual biomass shows potential to be used as a feedstock for fast pyrolysis bio-oil production for energetic and chemical use. Although environmentally advantageous, further catalytic upgrading is required in order to increase the bio-oil stability, by reducing reactive compounds, functional oxygen-containing groups and water content. However, bi...
Article
Full-text available
The potential to be able to control the structure of amorphous structure and establish correlations with their properties would constitute an extraordinary step for formulating new pathways to design and tailor amorphous structures and correspondingly would likely exhibit novel properties. Towards achieving this goal, a bottom-up approach is being...
Article
CAT-ACT—the hard X-ray beamline for CATalysis and ACTinide/radionuclide research at the KIT synchrotron radiation facility ANKA—is dedicated to X-ray spectroscopy, including “flux hungry” photon-in/photon-out and correlative techniques and combines state-of-the-art optics with a unique infrastructure for radionuclide and catalysis research. Measure...
Poster
Although thermoresistive catalytic combustion sensors are well established and have been used for decades the exact mechanisms on the molecular level are not fully clarified. To follow changes in the chemical state and crystalline structure of Rh nanoparticles we applied a combination of XAS, XRD and IR thermography for the study of sensors under r...
Article
Cr–Al–N coatings with a lateral composition gradient were deposited from two segmented Cr/Al targets with different segment size, thus covering the Al content range 0.22 ≲ c ≲ 0.87 and a thickness range from several hundred nanometres to several micrometres. The two-dimensional thickness and composition profiles were determined nondestructively fro...
Article
Natural aluminosilicates can contain Fe in tetrahedral or octahedral coordination. Amongst smectites, tetrahedral iron is known to occur in Fe-rich nontronites but few indications exist for the presence of tetrahedral Fe in smectites of the montmorillonite-beidellite series. A set of 38 different bentonites showed a correlation of tetrahedral charg...
Article
Full-text available
A new hard X-ray beamline for CATalysis and ACTinide research has been built at the synchrotron radiation facility ANKA. The beamline design is dedicated to X-ray spectroscopy, including 'flux hungry' photon-in/photon-out and correlative techniques with a special infrastructure for radionuclide and catalysis research. The CAT-ACT beamline will help...
Article
Full-text available
The dissolution parameters of calcium carbonates play a key role in agriculture as they regulate the plant nutrients uptake and buffer the pH-value of the soil. The combination of μXRF, μXAS and μXRD mapping in the hard X-ray regime for the examination of both short- and long range order in natural limestones revealed that their dissolution propert...
Conference Paper
Full-text available
Weight reduction is one of the major issues in many industrial areas. New structural materials which meet the highest standards, good mechanical properties, such as strength and ductility, and thermal stability are required. Aluminium and magnesium alloys attract particular attention because of their low density. Among various methods of manufactur...
Article
Highly crystalline α-MnO2 nanotubes with outer diameters between 25 and 40 nm are formed by a hydrothermal decomposition of KMnO4 precursor in an acidic environment. For nanotube formation, it is essential to include an addition of Fe3+ ions in the reaction mixture. SEM and TEM studies reveal that nanotubes are self-assembled into three-dimensional...
Article
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The combined investigation of the chemical bond formation in fluorinated multiwalled carbon nanotubes with 15wt.% fluorine concentrations (MWCNTs + F 15 wt.%) using X-ray absorption, emission and photoelectron spectroscopy at C1s and F1s thresholds is presented. All measurements were performed at BESSY II. The analysis of the soft X-ray and photoel...
Article
Full-text available
The L 2, 3 spectra of titanium in the layered compound TiSe2 and intercalated compounds Fe1/2TiSe2, Cr1/3TiSe2, and Fe1/4TiTe2 are studied. Theoretical calculations of the electronic structure of these compounds are performed. The experimental data and calculations suggest that the intercalation of the Cr and Fe atoms into the TiSe2 matrix brings a...
Article
Scanning electron microscopy (SEM) has long been a workhorse of materials science and provides information on morphology, structure and elemental composition. However, information as to the chemical state of the elements is only available for deep lying core levels of the heavy elements and not the light elements. Whilst considerable advances have...
Article
Radiative decay spectra of doubly excited states in He have been measured after selective excitation with monochromatized synchrotron radiation. The decay spectra are in excellent agreement with predictions based on calculations.
Thesis
Es wurde gezeigt, dass die Absorptions- und Emissionsspektroskopie weicher Röntgenstrahlung exzellente Werkzeuge für die Untersuchung der elektronischen Eigenschaften von nanostrukturierten Materialen sind. Die Volumensensitivität dieser Methoden ermöglicht es, die elektronische Struktur von vergrabenen Materialen und insbesondere Nanoröhrchen inne...
Article
Full-text available
Using photon-in photon-out soft x-ray spectroscopy, the electronic structure of silicon nanoclusters embedded in an electrically insulating SiO2 host matrix is investigated as a function of nanocluster size. We find the nanoclusters to be of a core-shell structure with a crystalline Si core and a thin transition layer of a suboxide. Effects of elec...
Article
Near edge x-ray absorption spectra at the Na K edge in aqueous NaCl electrolytes are presented as a function of concentration. The spectra are modeled by electronic structure calculations. We find and identify the orbital origin of two spectral fingerprints with sensitivity to the Na+-H2O distance and the Na+-Cl- distance in the electrolyte. Interi...
Article
X-ray absorption and emission spectroscopies are used to study the effects of short-ranged ordering on the electronic states of disordered GaN. Nanocrystalline samples with crystallites as small as 3 nm exhibit an electronic structure resembling a broadened version of that in crystalline GaN. The electronic structure is even more heavily broadened...
Article
The local electronic structure in subnanometer diameter MoS2-I-x nanotubes is investigated by soft X-ray absorption and X-ray fluorescence spectroscopies. The nanotubes are found to be semiconducting, with a band gap of 0.4 +/- 0.2 eV. The density of electronic states is altered in both the conduction and the valence band as compared to 2H-MoS2. El...
Article
Full-text available
We review our observations of surprisingly strong antiferromagnetic interlayer exchange coupling across Si-rich Fe 1−x Six spacers, which becomes stronger with increasing Si content, x, in the spacer. We show that the nominally pure (x = 1) spacers that mediate the strongest coupling act at the same time as a tunneling barrier for electric transpor...
Article
Full-text available
We discuss a soft X-ray emission (SXE) valence band (VB) spectroscopy method for the study of the electronic structure and chemical phase composition of solids in a near-surface region with depth resolution. The depth information is obtained by variation of the energy of the incident electron beam used to excite the SXE spectra. As the information...
Article
Full-text available
Soft x-ray absorption and emission spectroscopy is being used to study and compare the electronic structure of (a) potassium doped single wall carbon nanotubes (interstitial dopant), (b) LaatC82 (endohedral dopant) and (c) (C59N)2 (on-cage dopant). .

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