Hydrogenation on palladium nanoparticles supported by graphene nanoplatelets

Pd nanoparticles (1 wt %; mean size ∼4 nm) were supported on ∼2 μm sized, but few nanometers thick, graphene nanoplatelets (GNPs) and compared to 1 wt % Pd on activated carbon or γ-alumina. Catalyst morphology, specific surface area, and Pd particle size were characterized by SEM, BET, and TEM, respectively. H2-TPD indicated that GNPs intercalated hydrogen, which may provide additional H2 supply to the Pd nanoparticles during C2H4 hydrogenation. Whereas the two types of Pd/GNPs (NaOH vs calcinated) catalysts were less active than Pd/C and Pd/Al2O3 below 40 °C, at 55 °C they were about 3–4 times more active. As for example Pd/GNPs (NaOH) and Pd/Al2O3 exhibited not too different mean Pd particle size (3.7 vs 2.5 nm, respectively), the higher activity is attributed to the additional hydrogen supply likely by the metal/support interface, as suggested by the varying C2H4 and H2 orders on the different supports. Operando XANES measurements during C2H4 hydrogenation revealed the presence of Pd hydride. The Pd hydride was more stable for Pd/GNPs (NaOH) than for Pd/C, once more pointing to a better hydrogen supply by graphene nanoplatelets

Tuning interactions of surface‐adsorbed species over Fe−Co/K−Al2O3 catalyst by different K contents: selective CO2 hydrogenation to light olefins

Selective CO2 hydrogenation to light olefins over Fe−Co/K−Al2O3 catalysts was enhanced by tuning bonding strengths of adsorbed species by varying the content of the K promotor. Increasing the K/Fe atomic ratio from 0 to 0.5 increased the olefins/paraffins (O/P) ratio by 25.4 times, but then slightly raised upon ascending K/Fe to 2.5. The positive effect of K addition is attributed to the strong interaction of H adsorbed with the catalyst surface caused by the electron donor from K to Fe species. Although the Fe−Co/K−Al2O3 catalyst with K/Fe=2.5 reached the highest O/P ratio of 7.6, the maximum yield of light olefins of 16.4 % was achieved by the catalyst promoted with K/Fe of 0.5. This is explained by the considerable reduction of amount of H2 adsorbed on the catalyst surface with K/Fe=2.5

Ethanol steam reforming on ZnO and ZrO2 supported CuNi catalysts

Abweichender Titel laut Übersetzung der Verfasserin/des VerfassersZsfassung in engl. SprachePräparation und Charakterisierung von bimetallischen ZnO und ZrO2 geträgerten CuNi Katalysatoren. Bestimmung der katalytischen Eigenschaften in der Ethanoldampfreformierung, Untersuchung des Reaktionsmechanismus mittels in situ IR Spektroskopie und Temperatur-programmierter Desorption.Präparation und Charakterisierung von bimetallischen ZnO und ZrO2 geträgerten CuNi Katalysatoren. Bestimmung der katalytischen Eigenschaften in der Ethanoldampfreformierung, Untersuchung des Reaktionsmechanismus mittels in situ IR Spektroskopie und Temperatur-programmierter Desorption.8

LaCoO3 basierte Katalysatoren für die präferentielle CO Oxidation: Operando Spektroskopie

Abweichender Titel nach Übersetzung der Verfasserin/des VerfassersDie Erzeugung von Wasserstoff und Synthesegas (ein Gemisch aus CO und H2) spielt eine wichtige Rolle für Umwelt und Industrie. Wasserstoff ist ein vielversprechender zukünftiger Energieträger, und Synthesegas ist von großer Bedeutung für die Herstellung von gasförmigen oder flüssigen Kohlenwasserstoffen. Synthesegas kann u.a. durch Trockenreformierung von Methan (CH4) produziert werden (methane dry reforming MDR: CO2 + CH4 2CO + 2H2), wobei das Methan auch aus nicht-fossilen Quellen wie Bio-masse gewonnen werden kann. Aufgrund der niedrigeren Kosten von Erdgas und der Notwendigkeit Kohlendioxid zu recyclen, ist MDR zu einem vielversprechenden Weg zur Herstellung von Wasserstoff oder Synthesegas geworden. Die Aufreinigung von Wasserstoff (v.a. Entfernung von CO) ist ebenfalls ein industriell wichtiger Prozess, insbesondere für die NH3-Produktion und die mit Wasserstoff betrie-benen Protonenaustauschmembran (PEM)-Brennstoffzellen. Die katalytische präferenzi-elle CO-Oxidation (PROX), d.h. CO+H2+0.5O2CO2+H2, ist eine Schlüsselreaktion zur Entfernung von Spuren von CO aus dem H2-reichem Gasstrom. Übergangsmetalloxide, insbesondere kobaltbasierte Materialien, sind vielversprechende Katalysatoren für PROX. Das aktuelle Verständnis von PROX über diese Katalysatoren basiert jedoch hauptsächlich auf der Katalysatorcharakterisierung vor und nach der Reaktion und offene Fragen betreffen die Art der aktiven Zentren und Reaktionswege während der Reaktion ("operando"). Unter den attraktivsten Materialien der modernen chemischen Industrie (z.B. Katalyse, chemische Sensoren, Elektrodenmaterialien und Brennstoffzellen) haben sich in jüngster Zeit Perowskite als vielversprechendes und zu Übergangsmetalloxiden alternatives katalytisches Material etabliert. Das Interesse an Perowskit-Materialien vom ABO3-Strukturtyp, wobei A eine seltene Erde oder ein (Erd-)Alkali-Kation und B ein Übergangsmetallkation ist, erklärt sich durch einzigartige Eigenschaften des Perowskits, wie hohe Wärmeund Strukturstabilität der B-Kationen (z.B. Co3+), die diese Materialien beständig gegen Sintern und Reduktion machen, insbesondere für Hochtemperaturanwendungen. Das Hauptziel dieser Arbeit war, den Zusammenhang zwischen der Struktur der Perowskit-Materialien und ihren katalytischen Eigenschaften in PROX und MDR zu untersuchen. Dazu wurden Perowskit-Katalysatoren mit hoher Oberfläche und großer Homogenität synthetisiert und der Einfluss der CO- und H2-Reduktion auf die Struktur und den Oxidationszustand des Kobalt getestet. Weiterhin wurden verschiedene Vorbehandlungen (d.h. Oxidation und Reduktion) durchgeführt, um verschiedene Strukturtypen von Materialien zu erhalten, die für präferenzielle CO-Oxidation und MDR eingesetzt wurden. LaCoO3 (LCO) und LaNi0.2Co0.8O3 (LNCO) wurden durch eine optimierte Sol-Gel-Synthesemethode unter Verwendung von Zitronensäure (CA) und Ethylendiamintetraes-sigsäure (EDTA) als Komplexbildner hergestellt und der pH-Wert der Lösung mit Am-moniumhydroxid auf 9 eingestellt. Die Strukturen der erhaltenen Materialien nach der Kalzinierung wurden mit Hilfe von Röntgenbeugung (XRD), N2-Adsorption (BET), Transmissionselektronenmikroskopie bzw. hochaufgelöster TEM (TEM/HRTEM) und Rastertunnelmikroskopie (STM) untersucht. Die Reduktions-Oxidationseigenschaften der Materialien wurden durch CO-, H2-temperaturprogrammierte Reduktion (TPR) und O2-temperaturprogrammierte Oxidation (TPO) erforscht. Darüber hinaus wurden detaillierte kinetische Studien durchgeführt, um die katalytische Aktivität und Selektivität der Perowskit-Katalysatoren unter PROX- (LCO) und MDR- (LNCO und LCO) Reaktionsbedingungen zu bewerten. Operando XAS- und XRD-Spektroskopie-Studien wurden durchgeführt, um den Oxidationszustand und die Struktur der Perowskit-Katalysatoren während der PROX-Reaktion zu untersu-chen, wobei die katalytische Aktivität gleichzeitig mittels Massenspektrmetrie (MS) gemessen wurde. Um die atomare Struktur zu untersuchen, wurden operando-Röntgenabsorptionsspektroskopie-Studien (XAS) an der Co-K-Kante und operando zeit-aufgelöste Pulver-Röntgendiffraktion (XRD) durchgeführt. Operando diffuse Reflexions-Fouriertransformationsinfrarotspektroskopie (DRIFTS) wurde durchgeführt, um die Oberflächenspezies unter Reaktionsbedingungen zu untersuchen und Erkenntnisse über den Reaktionsmechanismus zu gewinnen. Zunächst wurde die Wirkung der verschiedenen Vorbehandlungen von LCO (oxidierte, bei unterschiedlichen Temperaturen reduzierte und reoxidierte Proben) für die PROX-Reaktion untersucht. Bei einer niedrigeren Reduktionstemperatur von 450C in H2 wurde LCO zu einer Brownmillerit-Struktur reduziert (Co2+, La2Co2O5) und bei einer höheren Reduktionstemperatur zu metallischem Kobalt (bei 650 C, Co0/La2O3). Katalytische Tests zeigten, dass die oxidierte LCO Probe mit Co3+ aktiver für die präferenzielle CO-Oxidation ist. Die bei niedriger Temperatur reduzierte Probe (bei 450 C, Co2+) zeigte eine hohe Selektivität gegenüber der Wasserstoffoxidation, während die bei hoher Temperatur reduzierte Probe (bei 650 C, Co0) zusätzlich die Methanisierung durch metallisches Kobalt katalysiert. Die CO-Oxidation an der reoxidierten Probe Co3O4/La2O3 (nach der Reduktion bei 650 C wurde die Probe bei 150 C reoxidiert) begann bei niedrigerer Temperatur als am metallisches Kobalt und am oxidierten LCO, aber das Selektivitätsfenster für diese Probe ist enger als am LCO, da die unerwünschte Wasserbildung früher einsetzt, ähnlich wie bei Co3O4. In weiterer Folge wurde das vielversprechendste Material LCO nach Oxidation hinsicht-lich struktureller Änderungen während der PROX Reaktion untersucht. LCO weist eine hohe Selektivität zur CO-Oxidation im Temperaturbereich von 100 - 220 C auf. Dar-über, bis etwa 300C, verläuft die CO-Oxidation parallel zur Wasserstoffoxidation (kon-kurrierende unerwünschte Reaktion). Über 300 C waren vor allem Wasserstoffoxidation und die umgekehrte Wassergas-Shift-Reaktion (RWGS) dominierend. Operando XAS und XRD während PROX zeigten, dass oxidiertes LaCoO3 die aktive Phase für die selektive Oxidation von CO zu CO2 im Temperaturfenster von 100-220 C ist. Über 300 C startete die Reduktion des Perowskits, und die Selektivität änderte sich von PROX in Richtung Wasserstoffoxidation und RWGS. Dies ist auf den Phasenwechsel von rhomboedrischem LaCoO3 (Co3+) zu monoklinem La3Co3O8 (Co2+ und Co3+) und orthorhombischem La2Co2O5 (Co2+) zurückzuführen. Mittels operando XAS, XRD und CO- und H2-TPR-Studien zeigte sich, dass die Redu-zierbarkeit von LCO in PROX naturgemäß geringer ist als in CO- oder H2-Atmosphäre, da unter PROX Bedingungen die Katalysatorreoxidation durch O2 schnell genug ist, und somit der Reduktionsgrad geringer ist. Die Reduktion von LCO in CO beginnt bei niedrigerer Temperatur als in Wasserstoff, was auf die Reaktion von CO mit Sauerstoffspezies auf der Katalysatoroberfläche zurückzuführen ist. Schließlich wurde MDR auf unterschiedlich vorbehandelte LNCO (Oxidation, Reduktion bei niedriger und höherer Wasserstoffkonzentration und Zumischen von zusätzlichem H2 während des MDR) untersucht. Interessanterweise zeigte die oxidierte Probe keine Aktivität im MDR, aber die reduzierte Probe eine hohe Aktivität für MDR. Die Konzentration des Reduktionsgases (5 Vol. % H2 vs. 0.5 Vol. % H2) verändert die MDR-Aktivität: Die niedrigere Konzentration des Gases führt zu einer höheren MDR-Aktivität. Daher führte die Zugabe einer niedrigen Wasserstoffkonzentration während des MDR (d.h. CO2 + CH4 und 0.5 vol.% H2) über der oxidierten LNCO Probe zu einer höheren MDR Aktivität und Stabilität im Vergleich zu LCO und reduzierter bzw. oxidierter Probe. Die Charakterisierung des gebrauchten LNCO- und LCO-Katalysators nach der Reaktion ergab, dass die Kristallstruktur des LNCO-Perowskits während der MDR verändert wur-de, aber eine Reoxidation dieses Materials bei 800 C führte dazu, dass das Material reversibel wieder in die ursprüngliche Perowskit-Struktur (LNCO) mit der gleichen Kristallgröße wie vor der Reaktion überging.The production of hydrogen and synthesis gas (a mixture of CO and H2) plays a major role for environment and industry as an energy source and for production of gas or liquid hydrocarbons. It is known that methane (CH4) can react with carbon dioxide and can be converted to synthesis gas via methane dry reforming (MDR: CO2 + CH4 2CO + 2H2). Methane can be obtained from other sources (e.g. biomass). Due to the lower cost of natural gas and the need for recycling of carbon dioxide, MDR has become a promising route to produce hydrogen or synthesis gas. Purification of hydrogen (CO removal) is also an industrially important process particu-larly for the NH3 production and hydrogen-fuelled proton exchange membrane (PEM) fuel cells. Catalytic preferential CO oxidation (PROX), i.e. CO+H2+0.5O2CO2+H2, is a key reaction for removing traces of CO from H2-rich streams. Transition metal oxides, especially cobalt-based materials, are promising catalysts for PROX. However, the cur-rent understanding of PROX over these catalysts is mainly based on preand post-reaction catalyst characterization and open questions include the nature of active sites and reaction pathways during reaction ("operando"). Among the most attractive materials in the modern chemical industry (e.g., catalysis, chemical sensors, electrode materials, and fuel cells), the perovskite oxides have recently emerged as very promising catalytic material, as alternative to transition metal oxides. The interest in perovskite materials of ABO3 structure type, where A is a rare earth/alkaline earth and B a transition metal cation, is explained by unique perovskite properties such as high thermal and structure stability of the B cations (e.g. Co3+ species), making these materials resistant towards sintering and reduction, especial for high-temperature applications. The main objective of this thesis was to investigate the correlation between the structure of the perovskite materials and their catalytic performance in PROX and methane dry reforming. For this, perovskite materials were synthesized with high surface area and high homogeneity and the effect of CO and H2 reduction on the structure and the oxidation state of the perovskite was evaluated. Further, different pretreatments (i.e., oxidation and reduction) were applied in order to obtain different structure types of materials, which were evaluated in PROX and MDR. LaCoO3 (LCO) and LaNi0.2Co0.8O3 (LNCO) materials were prepared by an optimized sol-gel synthesis methods using citric acid (CA) and ethylenediaminetetraacetic acid (EDTA) as complexation agents and ammonium hydroxide solution was used to adjust the pH to 9. The structures of the obtained materials were investigated using laboratory source X-ray diffraction (XRD), N2 adsorption, transmission electron microscopy/ high-resolution (TEM / HRTEM) and Scanning Tunneling Microscopy (STM). The reduction-oxidation properties of the materials were evaluated by CO-, H2- temperature programmed reduction (TPR) and O2-temperature oxidation (TPO). Furthermore, detailed kinetic studies were performed to evaluate catalytic activity and selectivity of the perovskite catalysts for PROX (LCO) and MDR (LNCO) reaction conditions. An advanced operando spectroscopy study was carried out to investigate the perovskite catalysts structure and oxidation state during the PROX reaction while simultaneously monitoring the catalytic activity by MS. To investigate the bulk structure, operando X-ray absorption spectroscopy studies (XAS) at the Co K -edge and operando time-resolved powder X-ray diffraction (XRD) were carried out. An operando diffuse reflectance infrared fourier transform spectroscopy (DRIFTS) was performed to study the surface species under reaction conditions and gain insights into the reaction mechanism. First, the effect of the different pretreatments (oxidized, reduced at different tempera-tures and re-oxidized samples) on the PROX reaction was investigated for LCO. High-temperature reduction in hydrogen and CO showed that the perovskite reduced stepwise. At a lower temperature, LCO reduced to brownmillerite (at 450 C, Co2+, La2Co2O5) and at a higher temperature to metallic cobalt (at 650 C, Co0/La2O3). The catalytic tests showed that the oxidized sample with Co3+ in LCO is more active for preferential CO oxidation. The low temperature reduced sample (at 450 C, Co2+) showed high selectivity to hydrogen oxidation, while the high temperature reduced sample (at 650 C, Co0) showed methanation due to metallic cobalt. The CO oxidation on the reoxidized sample (after reduction at 650 C, the sample was reoxidized at 150 C) started at a lower temperature than metallic cobalt and LCO, but the selectivity window for this sample is narrower than for LCO, similar to Co3O4. Afterwards, the catalytic activity and structural changes of LCO were studied during PROX. LCO demonstrates high selectivity of CO oxidation in the temperature range of 100 220 C. However, the CO oxidation proceeds up to 300 C with parallel hydrogen oxidation (undesired competitive reaction) starting above 300 C Above 300 C mainly hydrogen oxidation and reverse water gas shift were dominant. Operando XAS and XRD during PROX revealed that (unreduced) LaCoO3 is an active phase for selective oxidation of CO to CO2 in the 100-200 C temperature window. Above 300 C, perovskite reduction was initiated and accompanied by the selectivity change from PROX to hydrogen oxidation and RWGS due to phase change from LaCoO3 (Co3+) (rhombohedral) to monoclinic La3Co3O8 (Co2+ and Co3+) and orthorhombic La2Co2O5 (Co2+) brownmillerite-type perovskites. Operando XAS, XRD and CO- and H2 TPR studies found that the reducibility of LCO is apaprently more difficult in PROX than in CO or H2 atmosphere, because in PROX the catalyst re-oxidation by O2 is fast enough to prevent total reduction. The reduction of LCO in CO starts at a lower temperature than in hydrogen that is due to the reaction of CO with oxygen species on the catalyst surface. Finally, MDR was examined for differently pretreatreated LNCO (oxidized, low or high concentration reduced and additional reducing gas during MDR). Interestingly, while the oxidized sample was not active for MDR, the reduced sample showed high activity towards MDR. The concentration of the reducing gas (5 vol.% H2 vs 0.5 vol.% H2) changes the MDR activity: the lower concentration of H2 leads to higher MDR activity. Therefore, the usage of a low concentration of hydrogen during MDR (i.e., CO2 + CH4 and 0.5H2) on the oxidized sample led to a more active and stable MDR catalyst over 8 hours of time on stream compared to another sample, which was pretreated differently. The post characterization of the spent LNCO catalyst revealed that the crystal structure of the LNCO perovskite was destroyed during MDR but re-oxidation of this material at 800 C turned the material to the perovskite-type structure (LNCO) with same crystal size as before the reaction.14

Endovascular treatment of lower limb penetrating arterial traumas

Purpose: The purpose of this study was to evaluate the effectiveness of percutaneous arterial embolization in patients with penetrating peripheral arterial trauma.PURPOSE:The purpose of this study was to evaluate the effectiveness of percutaneous arterial embolization in patients with penetrating peripheral arterial trauma.MATERIALS AND METHODS:Twelve patients with penetrating peripheral arterial trauma were treated with percutaneous arterial embolization between 2002 and 2007. All injuries were secondary to penetrating stab wounds. Active bleeding (eight patients), recurrent bleeding episodes (one patient), persistent pain and mass (one patient), leg edema, claudication, swelling (one patient), local hyperemia, and pain (one patient) were the presenting symptoms. Microcatheter systems were used for catheterization. We used n-butyl cyanoacrylate mixture as the embolizing agent in all patients.RESULTS:On angiograms the inferior gluteal artery (one patient), internal pudendal artery (one patient), perforating branch of the profundal femoral artery (six patients), superficial femoral artery (one patient), peroneal artery (two patients), and anterior tibial artery (one patient) were found to be injured. In all patients, the source of arterial bleeding could be reached, and a safe embolization was achieved. Nontarget embolization due to backflow of n-butyl cyanoacrylate mixture was detected in two patients and inguinal hematoma at the puncture site occurred in one patient.CONCLUSIONS:We conclude that embolization-particularly n-butyl cyanoacrylate embolization-is technically feasible in patients with penetrating peripheral arterial trauma

Examining Pre-Service Physics Teachers’ Pedagogical Content Knowledge (PCK) with Web 2.0 Through Designing Teaching Activities

AbstractEmerging technologies require teachers to develop their PCK with technology. The aim of this study is to investigate the development of physics student teachers’ PCK with technology through designing teaching activities with web 2.0 tools. Data were gathered through a survey of open-ended questions and teaching activities designed by student teachers. Participants were 20 fourth grade prospective physics student teachers who took the course, “Technology-Assisted Physics Teaching”, in the spring term of 2011. The course consisted of 14 three-hour lectures and laboratories about using web 2.0 technologies in teaching physics. Information about web 2.0 technologies was provided and student teachers were asked to design activities as pairs and share and discuss them with other groups, under the guidance of the lecturer. Data from the survey were analysed using inductive content analysis and student teachers’ products were analysed using criteria of assessing ICT-TPCK. Findings revealed that most of the participants selected groups and blogs as platforms for sharing and discussing. Only six participants proposed wikis for students to establish wikis as dissemination of their work. Student teachers declared some advantages of web 2.0 technologies: their usage in and out of school, students’ active participation in learning process, opportunity to share information and ideas and collaboration. They also stressed that these tools supports student-centric learning activities and students take the responsibility of their own learning. However, it is concluded that student teachers did not have a clear idea or methodology how to integrate web 2.0 technologies into teaching physics

Modified pudendal thigh flap for perineoscrotal reconstruction: A case of Leriche syndrome with rapidly progressing Fournier's gangrene

We present the first report of Leriche syndrome associated with Fournier's gangrene. We used a modified pudendal thigh flap in the treatment of an extensive perineoscrotal soft-tissue defect successfully. We propose this new robust flap as an addition to the existing reconstructive armamentarium and draw attention to the coexistence of Leriche syndrome and Fournier's gangrene. (C) 2004 Elsevier Inc.We present the first report of Leriche syndrome associated with Fournier's gangrene. We used a modified pudendal thigh flap in the treatment of an extensive perineoscrotal soft-tissue defect successfully. We propose this new robust flap as an addition to the existing reconstructive armamentarium and draw attention to the coexistence of Leriche syndrome and Fournier's gangrene

Hybrid Adsorptive and Oxidative Removal of Natural Organic Matter Using Iron Oxide-Coated Pumice Particles

The aim of this work was to combine adsorptive and catalytic properties of iron oxide surfaces in a hybrid process using hydrogen peroxide and iron oxide-coated pumice particles to remove natural organic matter (NOM) in water. Experiments were conducted in batch, completely mixed reactors using various original and coated pumice particles. The results showed that both adsorption and catalytic oxidation mechanisms played role in the removal of NOM. The hybrid process was found to be effective in removing NOM from water having a wide range of specific UV absorbance values. Iron oxide surfaces preferentially adsorbed UV280-absorbing NOM fractions. Furthermore, the strong oxidants produced from reactions among iron oxide surfaces and hydrogen peroxide also preferentially oxidized UV280-absorbing NOM fractions. Preloading of iron oxide surfaces with NOM slightly reduced the further NOM removal performance of the hybrid process. Overall, the results suggested that the tested hybrid process may be effective for removal of NOM and control disinfection by-product formation