Core/Shell and Alloy Nanoparticles of Transition Metals for Heterogeneous Catalysis: Bridging the Gap between Experiment and Theory

This thesis describes the structural and catalytic properties of the architecturally-controlled bimetallic nanoparticles (NPs) of transition metals. In this study, bimetallic nanoparticles with well-defined architectures were synthesized, characterized and evaluated toward various heterogeneous reactions. Random alloy nanoparticles were compared to the core/shell nanoparticles (M@M' NPs where M is the core metal and M' is the shell metal), which is the synthetic counterpart of the theoretically well-studied Near Surface Alloys (NSAs). Thus, the long existing experimental gap with the theory can be bridged via the systematic evaluation of such architecturally-controlled bimetallic NPs. The M@Pt (M=Ru, Rh, Ir, Pd and Au) and Ru@M' (M'=Rh and Pd) core/shell NPs of tunable core sizes and shell thicknesses, and the PtRu alloy and PtRh alloy NPs of various compositions were prepared via poly-ol reduction reactions by using sequential deposition techniques. Seed NPs for the core/shell systems were synthesized via either poly-ol or NaBH4 reduction reactions. The wet-chemical co-deposition technique was employed to synthesize the alloy NPs. The core/shell and alloy NPs were characterized by using a combination of TEM, STEM-EDS, XRD, and FT-IR and Micro Raman -CO probe experiments. Full structural analysis employing techniques such as Extended X-Ray Absorption Fine Structure (EXAFS) and atomic Pair Distribution Function (PDF) was also performed for the 4.1 nm Ru@Pt NPs comprising of 3.0 nm cores and 1-2 MLs thick shells and the 4.4 nm Pt50Ru50 alloy NPs. Through collaborations, the nanoparticle structures were also modeled through EXAFS analyses, PDF fits, Rietveld Refinements and Debye Function simulations. The well-characterized core/shell and alloy NPs were evaluated for preferential oxidation of CO in H2 feeds (PROX). Catalytically, the core/shell NPs were superior to their alloy counterparts with similar particle sizes and identical compositions. The PROX reactivities of the M@Pt (M=Ru, Rh, Ir, Pd and Au) core/shell NPs increased in the order of Au@Pt 2-assisted O2 dissociation pathway on the electronically-altered Pt shells were suggested to bring on the room temperature CO oxidation and the subsequent H2 activation with enhanced PROX selectivity. The surface reactivities toward PROX and benzene hydrogenation reactions of the composition series of the PtRu alloy NPs exhibited the `Volcano' behavior, which invoked the Hammer-Norskov theory. The preliminary benzene hydrogenation results on the Ru@Pt NPs system presented in this study also showed a structure dependent correlation in surface activity

A Study on the Correlation of Leadership Styles and the Political Behaviours of Employees in Workplaces

Contemporary companies are giving considerable importance to satisfaction of their internal customers as well as satisfying their exterior customers by their goods and products. In tis context, employer branding-  an important concept developed by Simon Borrow- has been accepted as one of the most important developments of 1990s and myriad of companies has started to give importance to the mentioned point (Tüzüner, et al., 2009). Difficulties in finding talented employees, has made employer branding popular especially in service sector (Berthon vd. 2005; Knox and Freeman, 2006). According to information supplied from career portals, nowadays the highest number of job applications are being made to banking sector hence we were curious about this spesific sector in our study. Main sample of this study is composed of applicants that made job application to Albaraka Türk Participation Bank in the last three months prior to the design of this study. Aim of the study is measuring effects of employer branding dimensions in these applicant’s applicaitons behaviours and analyzing the relationship between their brand perceptions related to Albarak Türk Participation Bank and their levels of education and job experiences. With these purposes we used Berthon’s Employer Attractiveness Scale. Our survey has been applied to 500 job applicants from various education and experience levels and we used easy sampling method in choosing these applicants. Our survey, composed of 25 questions and Likert answer key with 7 answers has been brought to applicants via email and results have been analyzed by SPSS program. Our findings showed that rather than experience leves, education levels makes difference in appilicants perceptions about employer brand of the bank

Üniversite Öğrencilerinin İş Ahlakı Algısı ile Özel Sektör ve Kamu Çalışanlarının İş Ahlakı Uygulamalarının Karşılaştırılması

Bu ampirik araştırmada iş hayatı uygulamalarının belirlediği tutumlar ile üniversite öğrencilerin algıları karşılaştırılmıştır. Türkiye’de İstanbul ağırlıklı olmak üzere 135 üniversite öğrencisi, 148 özel sektör ve 117 kamu çalışanından elde edilen veriler deontolojik kuram temelinde bir yaklaşım ile analiz edilmiştir. Analizin ilk basamağında her üç grubun algı ve tutumları değerlendirilmiş, ikinci basamağında ise kamu-özel sektör çalışanlarının tutumları karşılaştırılmıştır. Sonuçlar, geleceğin çalışanları olacak öğrencilerin beklenti düzeyindeki iş ahlakı algılarının -ister kamu sektörü ister özel sektörde- çalışanların tutumlarından farklılaştığını, fakat çalışanlar grubu içinde böyle bir farklılığın olmadığını göstermesi bakımından anlamlıdır. Yine özel sektör ile kamu sektörü çalışanlarının iş ahlakı tutumlarındaki farklılaşmanın önemli ölçüde kamu sektörüne dair önermelerde ortaya çıkması, her iki sektör çalışanlarının iş hayatında sıkça karşı karşıya konumlanması neticesinde ortaya çıkmış görünmektedir

Challenging thermodynamics: hydrogenation of benzene to 1,3- cyclohexadiene by Ru@Pt nanoparticles

Since the earliest reports on catalytic benzene hydrogenation, 1,3-cyclohexadiene and cyclohexene have been proposed as key intermediates. However, the former has never been obtained with remarkable selectivity. Herein we report the first partial hydrogenation of benzene towards 1,3 cyclohexadiene under mild conditions in a catalytic biphasic system consisting of Ru@Pt nanoparticles (NPs) in ionic liquid (IL). The tandem reduction of [Ru(COD)(2-methylallyl)2] (COD = 1,5 cyclooctadiene) followed by decomposition of [Pt2(dba)3] (dba = dibenzylideneacetone) in 1-nbutyl- 3 methylimidazolium hexafluorophosphate (BMI.PF6) IL under hydrogen affords core-shell Ru@Pt NPs of 2.9 ± 0.2 nm. The hydrogenation of benzene (60 ºC, 6 bar of H2) dissolved in nheptane by these bimetallic NPs in BMI.PF6 affords 1,3- cyclohexadiene in unprecedented 21% selectivity at 5% benzene conversion. On opposition, almost no 1,3-cyclohexadiene was observed using monometallic Pt(0) or Ru(0) NPs under the same reaction conditions and benzene conversions. The study reveals that the selectivity is related to synergetic effects of the bimetallic composition of the catalyst material as well as the performance under biphasic reaction conditions. It is proposed that colloidal metal catalysts in ILs and under multiphase conditions (“dynamic asymmetric mixture”) can operate far from the thermodynamic equilibrium akin to chemically active membranes

Effect of the structure of Ni nanoparticles on the electrocatalytic activity of Ni@Pd/C for formic acid oxidation

Ni@Pd/C catalysts were synthesized, using Ni/C with different crystalline structures prepared with various ligands. A series of characterizations were performed by transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy. The results indicated the electrocatalysts with amorphous/crystalline (denoted as Nia and Nic) Ni structures decorated with Pd. The formic acid electrocatalytic oxidation results showed that the peak current of Nia@Pd/C was about 1.2 times higher than that of Nic@Pd/C. The good electrochemical performance and stability of Pd-modified amorphous Ni substrate reveals that the core structure plays an important role in the electrocatalytic activity and the change of the structure can improve the activity and stability of electrocatalysts.Web of Scienc

Montmorillonite modified by CNx supported Pt for methanol oxidation

A composite support based on nature clay, i.e. montmorillonite (MMT), shows great promise as support materials for Pt electrocatalyst for the methanol oxidation reaction in fuel cell anodes. The reported composite support (CNx-MMT) was prepared via carbonizing MMT which was covered by N-contented polymer. X-ray diffraction and transmission electron microscopy results showed that Pt nanoparticles can be well-dispersed on the composite support with highly dispersed tiny crystal Pt nanoparticles. Cyclic voltammetry measurements showed that the Pt/CNx-MMT has the enhanced electrocatalytic activity in methanol oxidation reaction. The developed Pt catalyst supported on new composite support is catalytically more active for methanol electrooxidation than Pt supported on the conventional carbon support and shows good stability, offering promising potential for application of MMT as support for fuel cell electrocatalysis.Web of Scienc

Room-temperature cycling of metal fluoride electrodes: Liquid electrolytes for high-energy fluoride ion cells

Fluoride ion batteries are potential “next-generation” electrochemical storage devices that offer high energy density. At present, such batteries are limited to operation at high temperatures because suitable fluoride ion–conducting electrolytes are known only in the solid state. We report a liquid fluoride ion–conducting electrolyte with high ionic conductivity, wide operating voltage, and robust chemical stability based on dry tetraalkylammonium fluoride salts in ether solvents. Pairing this liquid electrolyte with a copper–lanthanum trifluoride (Cu@LaF_3) core-shell cathode, we demonstrate reversible fluorination and defluorination reactions in a fluoride ion electrochemical cell cycled at room temperature. Fluoride ion–mediated electrochemistry offers a pathway toward developing capacities beyond that of lithium ion technology

In Situ Microscopy and Spectroscopy Applied to Surfaces at Work

The present review discusses the current state of the art microscopic and spectroscopic characterization techniques available to study surfaces and interfaces under working conditions. Microscopic techniques such as environmental transmission electron microscopy and in situ transmission electron microscopy are first discussed showing their applications in the field of nanomaterials and catalysis. Next sum frequency generation vibrational spectroscopy is discussed, giving probing examples of surface studies in gaseous conditions. Synchrotron based X-ray techniques are also examined with a specific focus on ambient pressure X-ray photoelectron and absorption techniques such as near and extended X-ray absorption fine structure. Each of the techniques is evaluated, whilst the pros and cons are discussed in term of surface sensitivity, spatial resolution and/or time resolution. The second part of the articles is articulated around the future of in situ characterization, giving examples of the probable development of the discussed techniques as well as an introduction of emerging tools such as scanning transmission X-ray microscopy, ptychography, and X-ray photon correlation spectroscopy

Shape-selected bimetallic nanoparticle electrocatalysts: evolution of their atomic-scale structure, chemical composition, and electrochemical reactivity under various chemical environments

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.Solid surfaces generally respond sensitively to their environment. Gas phase or liquid phase species may adsorb and react with individual surface atoms altering the solid-gas and solid-liquid electronic and chemical properties of the interface. A comprehensive understanding of chemical and electrochemical interfaces with respect to their responses to external stimuli is still missing. The evolution of the structure and composition of shape-selected octahedral PtNi nanoparticles (NPs) in response to chemical (gas-phase) and electrochemical (liquid-phase) environments was studied, and contrasted to that of pure Pt and spherical PtNi NPs. The NPs were exposed to thermal annealing in hydrogen, oxygen, and vacuum, and the resulting NP surface composition was analyzed using X-ray photoelectron spectroscopy (XPS). In gaseous environments, the presence of O2 during annealing (300 °C) lead to a strong segregation of Ni species to the NP surface, the formation of NiO, and a Pt-rich NP core, while a similar treatment in H2 lead to a more homogenous Pt-Ni alloy core, and a thinner NiO shell. Further, the initial presence of NiO species on the as-prepared samples was found to influence the atomic segregation trends upon low temperature annealing (300 °C). This is due to the fact that at this temperature nickel is only partially reduced, and NiO favors surface segregation. The effect of electrochemical cycling in acid and alkaline electrolytes on the structure and composition of the octahedral PtNi NPs was monitored using image-corrected high resolution transmission electron microscopy (TEM) and high-angle annular dark field scanning TEM (HAADF-STEM). Sample pretreatments in surface active oxygenates, such as oxygen and hydroxide anions, resulted in oxygen-enriched Ni surfaces (Ni oxides and/or hydroxides). Acid treatments were found to strongly reduce the content of Ni species on the NP surface, via its dissolution in the electrolyte, leading to a Pt-skeleton structure, with a thick Pt shell and a Pt-Ni core. The presence of Ni hydroxides on the NP surface was shown to improve the kinetics of the electrooxidation of CO and the electrocatalytic hydrogen evolution reactions. The affinity to water and the oxophilicity of Ni hydroxides are proposed as likely origin of the observed effects.DFG, EXC 314, Unifying Concepts in Catalysi