Particle size effect in methane activation over supported palladium nanoparticles

A synthesis method for producing MgAl oxide supported uniform palladium nanoparticles with varying diameters has been developed. The method consists of reductive-thermal decomposition of a PdMgAl hydrotalcite-like compound, formed via co-precipitation of metal nitrate salts and sodium carbonate. The hydrotalcite–like precursors were characterized by XRD, TG-MS and SEM, and were found to contain a well-defined crystalline structure and a uniform distribution of all constituent elements. The resulting catalysts were characterized by XRD, TEM, Chemisorption of CO and in situ IR measurements of CO, and were found to consist of partially oxide-embedded Pd nanoparticles with diameters ranging from d = 1.7 to 3.3 nm and correspond dispersions of 67–14%. Furthermore, the particle size was found to be inversely related to Pd loading. The palladium catalysts were studied for methane activation via chemisorption at 200 and 400 °C followed by a temperature programmed surface hydrogenation. The most disperse catalyst (d = 1.7 nm) possessed an intrinsic methane adsorption capacity, which was an order of magnitude larger than that of other catalysts in the series, indicating a strong structure sensitivity in this reaction. Additionally, the methane adsorption capacity of the hydrotalcite-derived Pd catalysts was nearly two orders of magnitude higher than that of catalysts derived through other synthesis pathways such as colloidal deposition or sonochemical reduction

Evolution of the electronic structure of Cs₂H₂PVMo₁₁O₄₀ under the influence of propene and propene/O₂

Evolution of the Electronic Structure of Cs2H2PVMo11O40 under the Influence of Propene and Propene/O2 J. Kröhnert, F.C. Jentoft, J. Melsheimer, R. Ahmad, M. Thiede, G. Mestl, and R. Schlögl Fritz-Haber-Institut der Max-Planck-Gesellschaft, 14195 Berlin, Faradayweg 4-6, Germany Changes in the electronic and vibrational spectra of Cs2H2PVMo11O40 in the presence of propene (1) or propene/O2 (2) were followed by in situ UV/Vis/NIR diffuse reflectance spec-troscopy. (1) At 298 K propene leads to reduction as indicated by a broad absorption band extending from the Vis to the NIR range. Iso-propanol was detected at 323 K and the maxi-mum of the broad band shifted from 740 to 700 nm. At higher temperatures the visible ab-sorption band shifted back about 25 nm. (2) Under conditions of catalytic oxidation a propene conversion of ca. 4% was detected with acrolein and CO as major products (670 K). Although the absorption band in the Vis range is less pronounced than in the presence of propene only at the same temperature, the catalyst is not restored to its fully oxidized state. The evolution of a band at 680-700 nm at 620-670 K indicates the formation of a structure with reduced and oxidized metal sites next to each other. This maybe related to the observation of molydenyl and vanadyl species in post mortem Raman spectra. 1. Introduction Cs salts of the vanadomolybdophosphoric acid are, for example, applied as catalysts for oxidative dehydrogenation of isobutyric acid to methacrylic acid [1-3]. The sensitivity of the catalyst under industrial operation suggests that the nature of the active phase may not be identical to the structurally well-defined salts which are molecular solids composed of Keggin ions, Cs cations, and water. Interestingly, the light-off temperature for oxidation reactions coincides with the temperature for the loss of constitutional water [4]. It is thus hypothesized that the water loss is connected to the formation of the active phase, whereby the electronic state of the active phase evolves in an atmosphere that contains both oxidative (O2) and re-ductive (hydrocarbon) components at the same time. In situ UV/Vis/NIR diffuse reflectance spectroscopy offers the unique possibility to si-multaneously investigate electronic features such as d-d transitions, intervalence charge trans-fers (IVCT), and ligand-to-metal charge transfers (LMCT) as well as the vibrational overtones and combination modes of water. From preliminary UV/Vis/NIR experiments, as from other methods (e.g., TG-DTA experiments), it has become clear that catalysts of the type CsxH4-xPVMo11O40 with x = 0-2 are already thermally unstable in the presence of an inert gas. This instability is expressed by the appearance and disappearance of absorption bands. The goal of this work was to investigate the loss of crystal and subsequently constitutio-nal water, and possible concomitant electronic changes of Cs2H2PVMo11O40 under inert, oxi-dative, and reductive conditions over a wide temperature range, as well as under the conditi-ons of oxidation catalysis. Propene was selected as a reactant and the gas phase was monito-red in order to correlate catalytic performance with spectroscopic data. 2. Experimental A Perkin-Elmer Lambda 9 spectrometer with an enlarged integrating sphere was used for in situ UV/Vis/NIR diffuse reflectance spectroscopy on different dilute catalyst samples. So-lutions of Cs2CO3 and heteropoly acid were used for the preparation of the Cs2H2PVMo11O40 samples. Approximately 110 mg of the catalyst (7-10 wt%) were mixed with SiO2 (Heraeus, 0.1-0.4 mm) and placed in a microreactor of in-house design operating under continuous gas flow. Sequential spectroscopic measurements were carried out with a scan speed of 240 nm/min, a slit width of 5.0 nm, and a response time of 0.5 s. Spectralon® was used as a refe-rence. The apparent absorption was evaluated from the diffuse reflectance data using the for-mula 1-Rmixture/RSiO2. The feed mixture was 10 vol-% propene in helium or 10 vol-% propene plus 10 vol-% oxygen in helium with a total gas flow of 71 or 74 ml/min, respectively. The gases were analyzed with two gas chromatographs (Perkin Elmer), equipped with heated au-tomatic gas sampling valves, an FFAP column (Macherey-Nagel) and a packed Carboxen-1000 column using FID and TCD in both GCs. Series A experiments (10% propene): The temperature was held constant for 2 h at room temperature (RT), and then the temperature was increased at a rate of 1 K/min to 323 K, and spectra were recorded over a period of ca. 5 hours. Series B experiments (10% propene): The temperature was increased from RT to 323 K and then to 670 K in steps of ~ 50 K (5 K/min heating rate), with a 2 h isothermal period after each step. Series C experiments (10% propene, 10% O2): The temperature was increased as in Series B with extended isothermal periods of 9 h at 413 K and 19 hours at 670 K. 3. Results The Series A spectra show a strong increase in apparent absorption already at RT. After 40 min on stream (RT3 in Fig. 1) a visible absorption band formed at ~ 740 nm and this band underwent a blue shift to 700 nm when the temperature was increased to 319 K. In contrast to similar experiments using He, the crystal water bands at 1430 and 1925 nm already disappear after 70 min on stream (Figure 1). Formation of iso-propanol was detected at 319 K. Series B spectra showed similarly strong changes in apparent absorption with a red shift of ca. 25 nm for the visible absorption band and the appearance of an additional band in the NIR (at ~ 1050 nm). The NIR band (appearing above 560K) is broad and overlaps with the visible band (Fi-gure 2). The visible band increases with increasing temperature until a single broad visi-ble/NIR band forms. For Series C, increasing temperature leads to a decrease in the intensity of the absorption bands, particularly the NIR band (Figure 3). However, the visible band be-comes clearly recognizable again at 563 K; it is possible that a catalytic reaction begins to occur at this temperature. The products acrolein, propionic acid, acrylic acid and water were first detected at 603 K. At 670 K in addition to these products we also detected propionalde-hyde, acetone, CO and acetic acid, with the conversion of propene being ca. 4% and that of O2 ca. 12 %, and the highest selectivities being for acrolein and CO. In the Series C spectra the defined feature in the UV region does not disappear as it did in the Series B spectra at higher temperatures. Under catalytic reaction conditions above 563 K one observes an increase in the intensity of the shifted visible absorption band at 680-700 nm with increasing temperature (=620 K) and time on stream (Figure 4). 4. Discussion The water bands disappear much more readily in the presence of propene than in inert gas, and at the same time, isopropanol is formed. These observations can be explained by an addition of water from the catalyst to propene, a typical acid-catalyzed reaction. Propene thus appears to draw the crystal water from the catalyst, and when the crystal water is gone the constitutional water is removed as well. The sample apparently underwent considerable re-duction even at the relatively low temperature of propene hydration, which corresponds to the observations in inert gas at higher temperature, and reduction generally seems to accompany the water loss. Hence, water, which is added in the industrial oxidation process, may play an essential role in maintaining a certain, i.e. active, state of the catalyst which is different from a van-der-Waals solid built of isolated Keggin units. The electronic structure change in the pre-sence of propene is dramatic; the defined LMCT band is obscured by an intense, almost con-tinuous absorption which is even more pronounced at higher temperatures (up to 670 K). The catalyst sample was black after treatment with the propene atmosphere, in contrast to He-treated catalyst samples that were blue [5]. In the presence of propene and oxygen, the initial reduction at 555 K is partly reversed at 620-670K; however, although excess oxygen is available the catalyst remains in a reduced state. The decrease in the intensity of the visible absorption band below the catalytic reaction temperature (603K) may be attributed to an oxidation of some Mo5+ and V4+ centers by the gas phase oxygen. Above this temperature the absorption band increases with rising tempera-ture through the stronger reduction of the catalyst and at the same time the conversion also increases. The blue shifted absorption band at ca. 680 nm that was observed at 670K could indicate oxygen vacancies that are important for the oxidation reactions. These species may be the same as a species observed in post mortem Raman analysis of these samples that was charac-terized by a shoulder at about 1002 cm-1 and was interpreted as molybdenyl species [6]. Un-der the same conditions, the free acid H4PVMo11O40 showed a blue shift up to 660 nm [5], which might indicate the presence of molybdenyl and vanadyl species in the catalyst sample, since Raman bands were in turn detected at 1008 and 1030 cm-1 [6]. In summary, the changes in electronic structure appear too dramatic to be just a conse-quence of a partial reduction of the Keggin ion; rather it seems that the geometric structure is partially dissolved leading to a transformation from a molecular solid to more condensed oxi-dic species with semiconducting character. The availability of relatively free electrons that is suggested by the continuous character of the UV/Vis spectra at high temperatures is a prere-quisite for the activation of molecular oxygen and thus for the redox catalytic activity. The structural changes are too severe to allow the restoration of the heteropolyacid through the water that is formed in the propene oxidation; and acidic properties also no longer play a role for the product distribution under these conditions. References 1. M. Misono, N. Nojiri, Appl. Catal., 64 (1990) 1. 2. Th. Ilkenhans, B. Herzog, Th. Braun and R. Schlögl, J. Catal., 153 (1995) 275. 3. L. Weismantel, J. Stöckel and G. Emig, Appl. Catal., 137 (1996) 129. 4. S. Berndt, Dissertation, TU Berlin, 1999. 5. J. Kröhnert, O. Timpe, J. Melsheimer, F.C. Jentoft, G. Mestl and R. Schlögl, to be pub-lished. 6. G. Mestl, T. Ilkenhans, D. Spielbauer, M. Dieterle, O. Timpe, J. Kröhnert, F.C. Jentoft, H. Knözinger and R. Schlögl, Appl. Catal. A, submitted

Towards the pressure and material gap in heterogeneous catalysis: hydrogenation of acrolein over silver catalysts

Introduction In recent time, increasing effort has been undertaken in order to answer the question, whether it is justified to transfer results from surface science studies, mostly obtained with idealised surfaces under UHV conditions, to "real" catalysis, i.e. high pressures and complex materials (the so-called pressure and material gaps). The DFG (German research foundation) has initialised a priority program (SPP 1091) in order to bring together experts from surface science, materials science, catalysis and theory with the aim of bridging the two gaps in catalysis. Within this priority program, we are currently studying the hydrogenation of acrolein over silver. Acrolein, an ,-unsaturated aldehyde, can be hydrogenated either to propanal (product of C=C-bond hydrogenation) or to allyl alcohol (product of C=O-bond hydrogenation. Whereas typical hydrogenation catalysts like Pt, Ru or Ni mainly produce the saturated aldehyde, selectivities to allyl alcohol of up to 53 % can be obtained when using monometallic silver (or gold) catalysts [ , ]. The aim of our studies is to clarify the influence of reaction pressure and material on the selectivity distribution in the acrolein hydrogenation. Catalytic experiments have been carried out with differently structured samples from single crystals to disperse Ag/support catalysts in a broad pressure range (few mbar up to 20 bar). Various methods like in situ-XAS and XPS, flow-adsorption calorimetry, infrared spectroscopy, and transient analysis of products (TAP) are performed in order to gain insight into the modes of interaction of acrolein and hydrogen with differently structured silver samples. Effects of particle size and shape are also considered as well as the influence of the support material. Experimental and Results would add a few words about the composition (Ag loading, different supports) / preparation of the catalysts and/or a reference Gas phase hydrogenation of acrolein has been carried out in a flow reaction system allowing a pressure in the range from 150 mbar up to 20 bar. When using silica supported silver catalysts, clear relations can be drawn concerning the pressure and material dependence of the selectivity to allyl alcohol: increasing partial pressure of either reactant (hydrogen or acrolein) leads to increased selectivity to allyl alcohol, also, smaller particles favour its formation. However, when using ZnO-supported catalysts, the situation becomes more complex. Catalysts prepared with the same catalyst loading and the same catalyst preparation technique but with different ZnO support materials yielded different selectivities to allyl alcohol at the same conversion. On the other hand, catalysts prepared from different precursors, but with the same support, lead to different activities but similar selectivities to allyl alcohol. TEM investigations of the Ag/ZnO and Ag/SiO2 catalysts reveal, that the particle sizes of the silica-supported catalysts are much smaller (2 nm and 15 nm in average for the two most intensively studied catalysts) whereas the silver particles in the Ag/ZnO catalysts are surprisingly large (50 nm up to several hundreds of nm). This is even more surprising since the activities of the catalysts are in the same order of magnitude, with the SiO2 catalysts however, being a bit more active. All these results indicate, that the product distribution at supported silver catalysts is governed by a complex interplay between particle size (and/or shape), pressure, and, as the obviously most important factor, the support and the interactions between silver and support. To gain more insight into the reasons for the catalytic behaviour of the Ag/support catalysts, the interaction of hydrogen alone with various silver samples has been studied. TAP (temporal analysis of products) indicates, that hydrogen interacts with nanodisperse Ag/SiO2 samples, but not with larger unsupported silver particles (several mm in size) like those from electrolyte silver. However, as monitored by transmission infrared spectroscopy, not only the Ag nanoparticles but also the SiO2 support interacts with hydrogen. SiO2 and Ag/SiO2 samples, after reduction and exposure to 100 mbar D2, show a reversible H-D-exchange, as monitored by the Si-O-H(D) bands. Time resolved IR spectra indicate, that this H-D-exchange is faster at silver-containing samples. From temperature-dependent measurements, activation energies for the H-D-exchange of ca. 28 kJ/mol for Ag/SiO2 and ca. 38 kJ/mol for SiO2 have been calculated. The interaction of acrolein with silver single crystals as well as with supported catalysts has been studied with in-situ-XAS and in-situ XPS. For both techniques the samples were contacted with mixtures of H2/acrolein in the mbar pressure range. Angular dependent XAS measurements on a Ag(111) single crystal indicated that acrolein is in the lying-down orientation. For all the samples measured the 1π* “C=O” transition is clearly increased compared to the 1π* “C=C”. Consequently, the surface concentration of C=O bonds relative to C=C bonds is higher, which is in line with concomitantly measured mass spectrometric data showing high selectivity towards C=C hydrogenation. In-situ XPS revealed that while silver foil is partly oxidic (~5%) the supported silver particles are completely reduced, as Ag is in the zero valence state. Data indicate also small amount of oxygen removal from the ZnO supported samples during the contact with hydrogen. The combination of different results suggests that metal-support interaction plays an important role in the reaction. The major difference in hydrogen activation between supported catalysts and pure silver/support provides us a hint that the so-called “adlineation sites” (the perimeter interface between silver and support) are the key sites in the mechanism

Einfluss von Temperatur und Gasphase auf Cs_xH_4-xPVMo₁₁O₄₀ (x=0,2): In situ UV/Vis/NIR-Spektroskopie

Einfluß von Temperatur und Gasphase auf CsxH4-xPVMo11O40 (x=0,2): In situ UV/Vis/NIR-Spektroskopie J. Melsheimer, J. Kröhnert, M. Thiede, G. Mestl, F.C. Jentoft, R. Schlögl Fritz-Haber-Institut der Max-Planck-Gesellschaft Faradayweg 4-6, D-14195 Berlin - Einführung in die Problemstellung Cs-Salze der Vanadomolybdophosphorsäure finden technischen Einsatz für die Methacrylsäuresynthese [1]. Die Natur der aktiven Phase, die sich wahrscheinlich erst bei erhöhter Temperatur im sowohl oxidative als auch reduktive Komponenten enthaltenden Reaktionsgas bildet und eine Zwischenstufe zwischen molekularen (Keggin-Einheiten) und polymeren Spezies (Endprodukt MoO3) darstellen könnte, ist unbekannt. Die Aktivierung unter inerten (He), oxidativen (O2) und reduktiven (Propen) Bedingungen wurde in situ mit UV/Vis/NIR- Spektroskopie in Diffuser Reflexion verfolgt. - Experimentelles H4PVMo11O40 (H4A) und Cs2H2PVMo11O40 (Cs2A), hergestellt über das Oxidverfahren [2] sowie durch Fällung mit Cs2CO3, wurden mit vorgesintertem SiO2 verdünnt (10 Gew.% CsxA). Die Proben wurden im gewünschten Gasstrom (50-70 ml/min, p = 1 atm) in einer selbst entwickelten in situ Zelle mit 5K/min bis 723K erhitzt, und während zwei-stündiger Haltezeiten bei bestimmten Temperaturen (ca. alle 50K) wurden Spektren (Perkin Elmer Lambda 9, BaSO4-beschichtete Integrationskugel, di=60 mm) aufgenommen. Wurde Propen eingesetzt, wurde das Reaktorabgas gaschromatographisch analysiert. - Zusammenfassung der Ergebnisse und Schlußfolgerungen Die Ausgangsspektren von H4A und Cs2A sind durch Banden bei ca. 1925, 1470 (sehr schwach) und 1420 nm gekennzeichnet. Diese Banden können Ober- und Kombinationsschwingungen von OH-Gruppen zugeordnet werden und zeigen den Kristallwassergehalt der Probe an. Außerdem wird eine Bande bei 720 nm (H4A) beobachtet, die vermutlich einem Intervalenz-Charge-Transfer (IVCT) Übergang von V4+ zu Mo6+ zugeordnet werden kann. Die durch die erste Ableitung bestimmte Bandkante von H4A lag bei 2.2 eV. Inerte Atmosphäre (He): Bereits bei 373K(H4A) bzw. 403K (Cs2A) sind in den Spektren keine definierten OH-Schwingungen mehr zu erkennen, übereinstimmend mit dem Verlust von Kristallwasser, der sich in TG-Messungen durch eine Gewichtsabnahme von ca. 4,5% (Cs2A) und 7,5 % (H4A) bis 423 K äußert. Gleichzeitig bildet sich eine Absorptionsbande aus, die sich von 670 (H4A) bzw. 720 (Cs2A) bis ca. 1150 nm erstreckt und Maxima bei 720 (H4A) und 750 (Cs2A) nm sowie um 950 nm aufweist. Diese Banden könnten auch IVCT- Übergängen von V4+ zu Mo6+ zuzuordnen sein und zeigen die partielle Reduktion der Proben an. Ab etwa 418K bis 643K verstärkt sich die Absorption im Bereich 600 bis 800 nm mit Maxima bei 660 (H4A) und 680-700 nm (Cs2A), was auf eine zunehmende Reduktion hindeutet wie auch die grüne Probenfarbe. Oxidative Atmosphäre (reiner O2): Bis 373K unterscheiden sich die Spektren nicht signifikant von den Messungen im Inertgas. Im Bereich 418-643K weisen beide Kataly-satoren in dem o.a. Wellenlängenbereich schwächere Absorptionsbanden als in He auf, d.h. im Sauerstoffstrom unterliegen sie während des Verlustes an konstitutionellem Wasser möglicherweise simultan Reduktions- und Oxidationsvorgängen. Reduktive Atmosphäre (10% Propen in He): Im Vergleich zur inerten/oxidativen Umgebung verschwinden die OH-Banden bei beiden Substanzen wesentlich schneller, d.h. bereits nach 105 min bei RT, und die Spektren zeigen eine sehr intensive Absorption über den gesamten Vis-Bereich. Bei 323K wird im Abgasstrom i-Propanol detektiert, d.h. Propen entzieht den Proben Kristallwasser unter Bildung des Alkohols, entsprechend einer typischen säurekatalysierten Reaktion. Bei höheren Temperaturen scheinen die Bandkanten zu verschwinden, die Reflektivität sinkt erheblich, und die Proben verfärben sich schwarz. Gemischte Atmosphäre (10% Propen + 10% O2 in He): Die Oxidation von Propen setzt in Gegenwart von H4A bei 513K ein, wobei die Hauptprodukte (verantwortlich für >90% des Propen- bzw. O2-Umsatzes) Wasser, Acrolein und Essigsäure gebildet werden. Die Starttemperatur in Gegenwart von Cs2A beträgt 617K, und es wird ein breiteres Produktspektrum detektiert, das als Hauptprodukte Wasser, Acrolein, CO, Propanal, Essigsäure und Aceton enthält. Für beide Katalysatoren wird mit zunehmender Temperatur eine Bande bei 690-700 nm beobachtet, deren Intensität oberhalb von 563K stark ansteigt. Diese Bande könnte für die Oxidationsreaktion wichtige Sauerstoffehlstellen anzeigen. - Literatur [1] M. Misono, N. Nojiri, Appl. Catal., 64 (1990) 1. [2] E.O. North, Inorg. Synth., I (1939) 127

Mass changes of southern and northern inylchek glacier, Central Tian Shan, kyrgyzstan, during ∼1975 and 2007 derived from remote sensing data

Glacier melt is an essential source of freshwater for the arid regions surrounding the Tian Shan. However, the knowledge about glacier volume and mass changes over the last decades is limited. In the present study, glacier area, glacier dynamics and mass changes are investigated for the period ∼1975-2007 for Southern Inylchek Glacier (SIG) and Northern Inylchek Glacier (NIG), the largest glacier system in Central Tian Shan separated by the regularly draining Lake Merzbacher. The area of NIG increased by 2.0 ± 0.1 km2 (∼1.3%) in the period ∼1975-2007. In contrast, SIG has shrunk continuously in all investigated periods since ∼1975. Velocities of SIG in the central part of the ablation region reached ∼100-120 m a-1 in 2002/2003, which was slightly higher than the average velocity in 2010/2011. The central part of SIG flows mainly towards Lake Merzbacher rather than towards its terminus. The measured velocities at the distal part of the terminus downstream of Lake Merzbacher were below the uncertainty, indicating very low flow with even stagnant parts. Geodetic glacier mass balances have been calculated using multioral digital elevation models from KH-9 Hexagon (representing the year 1975), SRTM3 (1999), ALOS PRISM (2006) and SPOT-5 high-resolution geometrical (HRG) data (2007). In general, a continuous mass loss for both SIG and NIG could be observed between ∼1975 and 2007. SIG lost mass at a rate of 0.43 ± 0.10 m w.e. a-1 and NIG at a rate of 0.25 ± 0.10 m w.e. ag-1 within the period ∼1975-1999. For the period 1999-2007, the highest mass loss of 0.57 ± 0.46 m w.e. ag-1 was found for NIG, whilst SIG showed a potential moderate mass loss of 0.28 ± 0.46 m w.e. a-1. Both glaciers showed a small retreat during this period. Between ∼1975 and 1999, we identified a thickening at the front of NIG with a maximum surface elevation increase of about 150 m as a consequence of a surge event. In contrast significant thinning (>0.5 m a-1) and comparatively high velocities close to the dam of Lake Merzbacher were observed for SIG, indicating that Lake Merzbacher enhances glacier mass loss.Publisher PDFPeer reviewe

Systematic comparison of the effects of Alpha-synuclein mutations on its oligomerization and aggregation

Copyright: © 2014 Lázaro et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.Aggregation of alpha-synuclein (ASYN) in Lewy bodies and Lewy neurites is the typical pathological hallmark of Parkinson's disease (PD) and other synucleinopathies. Furthermore, mutations in the gene encoding for ASYN are associated with familial and sporadic forms of PD, suggesting this protein plays a central role in the disease. However, the precise contribution of ASYN to neuronal dysfunction and death is unclear. There is intense debate about the nature of the toxic species of ASYN and little is known about the molecular determinants of oligomerization and aggregation of ASYN in the cell. In order to clarify the effects of different mutations on the propensity of ASYN to oligomerize and aggregate, we assembled a panel of 19 ASYN variants and compared their behaviour. We found that familial mutants linked to PD (A30P, E46K, H50Q, G51D and A53T) exhibited identical propensities to oligomerize in living cells, but had distinct abilities to form inclusions. While the A30P mutant reduced the percentage of cells with inclusions, the E46K mutant had the opposite effect. Interestingly, artificial proline mutants designed to interfere with the helical structure of the N-terminal domain, showed increased propensity to form oligomeric species rather than inclusions. Moreover, lysine substitution mutants increased oligomerization and altered the pattern of aggregation. Altogether, our data shed light into the molecular effects of ASYN mutations in a cellular context, and established a common ground for the study of genetic and pharmacological modulators of the aggregation process, opening new perspectives for therapeutic intervention in PD and other synucleinopathies.This work was supported by the DFG Center for Nanoscale Microscopy and Molecular Physiology of the Brain (CNMPB).info:eu-repo/semantics/publishedVersio

Nanopartikel auf subnanometer dünnen oxidischen Filmen: Skalierung von Modellsystemen

Durch die Abscheidung von ultradünnen Oxidschichten auf atomar‐flachen Metalloberflächen konnte die elektronische Struktur des Metalls und hierdurch dessen katalytische Aktivität beeinflusst werden. Die Skalierung dieser Architekturen für eine technische Nutzbarkeit war bisher aber kaum möglich. Durch die Verwendung einer flüssigkristallinen Phase aus Fluorhectorit‐Nanoschichten, können wir solche Architekturen in skalierbarem Maßstab imitieren. Synthetischer Natriumfluorhectorit (NaHec) quillt spontan und repulsiv in Wasser zu einer nematischen flüssigkristallinen Phase aus individuellen Nanoschichten. Diese tragen eine permanente negative Schichtladung, sodass selbst bei einer Separation von über 60 nm eine parallele Anordnung der Schichten behalten wird. Zwischen diesen Nanoschichten können Palladium‐Nanopartikel mit entgegengesetzter Ladung eingelagert werden, wodurch die nematische Phase kollabiert und separierte Nanopartikel zwischen den Schichten fixiert werden. Die Aktivität zur CO‐Oxidation des so entstandenen Katalysators war höher als z. B. die der gleichen Nanopartikel auf konventionellem Al2O3</sub oder der externen Oberfläche von NaHec. Durch Röntgenphotoelektronenspektroskopie konnte eine Verschiebung der Pd‐3d‐Elektronen zu höheren Bindungsenergien beobachtet werden, womit die erhöhte Aktivität erklärt werden kann. Berechnungen zeigten, dass mit erhöhter positiver Ladung des Pd die Adsorptionsstärke von CO erniedrigt und damit auch die Vergiftung durch CO vermindert wird

Towards Experimental Handbooks in Catalysis

The “Seven Pillars” of oxidation catalysis proposed by Robert K. Grasselli represent an early example of phenomenological descriptors in the field of heterogeneous catalysis. Major advances in the theoretical description of catalytic reactions have been achieved in recent years and new catalysts are predicted today by using computational methods. To tackle the immense complexity of high-performance systems in reactions where selectivity is a major issue, analysis of scientific data by artificial intelligence and data science provides new opportunities for achieving improved understanding. Modern data analytics require data of highest quality and sufficient diversity. Existing data, however, frequently do not comply with these constraints. Therefore, new concepts of data generation and management are needed. Herein we present a basic approach in defining best practice procedures of measuring consistent data sets in heterogeneous catalysis using “handbooks”. Selective oxidation of short-chain alkanes over mixed metal oxide catalysts was selected as an example.DFG, 390540038, EXC 2008: Unifying Systems in Catalysis "UniSysCat