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Burkardt, Sven. « Oxide and oxide supported nanoclusters on quasicrystals ». Berlin Logos-Verl, 2009. http://d-nb.info/999419471/04.
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Teng, Die. « Computational studies of transition metal nanoclusters on metal-supported graphene moiré ». Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/51830.
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The graphene moiré superstructure formed on Ru(0001) (g/Ru(0001)) has shown the potential as a template to self-assemble super-lattices of metal nanoparticles as model catalysts. To explore the possibility of rational catalyst design on g/Ru(0001), detailed density functional theory (DFT) calculations have been performed to investigate the adsorption and diffusion of Rh and Au adatoms on g/Ru(0001). The consequences of different hopping rates for cluster nucleation have been explored by performing Monte Carlo-based statistical analysis, which suggests that diffusing species other than adatoms need to be taken into account to develop an accurate description of cluster nucleation and growth on this surface. DFT calculations have also been carried out to investigate the adsorption and diffusion of 18 4d (Y-Ag) and 5d (La-Au) transition metal adatoms on g/Ru(0001). Given the necessity to study larger diffusing species than adatoms, DFT calculations have been performed to study the adsorption and diffusion of Rh and Au dimers and trimers on g/Ru(0001). It was shown that the mobility of Rh clusters decreases with the increase of cluster size, while for Au, dimers diffuse faster than monomers and trimers on the moiré surface. We then used a genetic algorithm combined with DFT calculations to predict the lowest energy structure of a Au8 cluster on g/Ru(0001). Our prediction leads us to propose that Au clusters aggregates through Oswald ripening with Au dimer being the major diffusing species. Finally, we examined the morphology of a Cu19 cluster on g/Cu(111) using MD simulations with COMB3 potential. We also studied the mobility of Cu clusters on g/Cu(111) at elevated temperatures. The analysis suggests that g/Cu(111) may not be a suitable substrate for the formation and growth of isolated Cu clusters. All these calculation results have provided us a better understanding and useful insights into the nucleation and growth mechanism of metal clusters on graphene moiré.
3
Golfetto, Enrico. « Electronic structure and chemical reactivity of transition metals' pseudomorphic layers and supported nanoclusters ». Doctoral thesis, Università degli studi di Trieste, 2010. http://hdl.handle.net/10077/3580.
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2008/2009The importance of heterogeneous catalysis in chemical industry and its economic impact in today‟s society motivate the continuous research effort in this field. Transition metals are among the main ingredients of commercial catalysts due to their chemical properties which depend on their surface morphological and electronic structure. It is well known that their catalytic properties can be further improved by tuning particle size in the nanometre range or by alloying different transition metals. Nowadays it is possible to predict the variation of surface chemical properties on the basis of the d-band centre energy position, which is actually considered as one of the most reliable depicters of chemical reactivity. This physical quantity cannot be easily accessed by experimental measurement and is typically calculated using a theoretical approach. A promising approach to establish an experimental relationship between electronic structure and chemical reactivity relies on the use of X-ray Photoelectron Spectroscopy with third generation synchrotron radiation sources. Indeed, the high resolution achieved in the recent years has allowed the identification of the contributions originated from bulk and surface atoms in the core level photoemission spectra,thus determining what is usually named Surface Core Level Shift (SCLS). It has been shown that SCLS is a valuable probe of surface electronic structure, since the core level binding energy of an atom depends strongly on the local structural and chemical environment. In this thesis, the electronic structure modification induced by reduced coordination, surface strain, atomic rearrangement and ligand effects are investigated in different systems by means of High Energy Resolution Core Level Spectroscopy experiments, on several systems with different complexity. Pseudomorphic states of Pd, grown on a Ru(0001) surface, have been studied by comparing the calculated d-band center shifts of the differently coordinated atoms to the measured core level shifts of the same species, finding a strong relationship between these two physical quantities. For two of structures (1- and 2-Pd MLs/Ru(0001)) we tested the chemical reactivity by exposing the surfaces to oxygen. The results confirmed the relationship between d-band center shift, CLS and chemical reactivity. A more complex system is the one composed by Pd nanoclusters on Single Walled Carbon NanoTubes (SWCNTs), Highly Ordered Pyrolythic Graphite (HOPG) and Ir supported graphene sheet. The most relevant feature is the formation of a high BE component in Pd 3d5/2 spectrum, induced by those Pd atoms coordinated with surface defects. This interpretation has been suggested by the comparison of experimental results with the calculations on Pd/HOPG core level shifts for many different atomic species. For Pd/SWCNTs we studied also the oxidation mechanisms, ranging on a wide spectrum of oxidation conditions. Our results confirm the presence of a 2D oxide phase, as previously found on Pd single crystal, with some different behaviour induced by the reduced size of our particle Finally, the growth mechanisms and the chemical reactivity of Pt nanoclusters, supported on a MgO thin film has been studied by both energy and time resolved x-ray photoemission spectroscopy. The CO oxidation reaction has been investigated for different temperatures and different clusters‟ size, resulting also in a deeper comprehansion of the clusters‟ morphology.
XXII Ciclo
1979
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Zhang, Man. « Design, synthesis, and evaluation of bioactive molecules ; Chiral polyvinylpyrrolidones supported Cu/Au nanoclusters catalyzed cyclization of 5-substituted nona-1,8-dien-5-ols ». Diss., Kansas State University, 2017. http://hdl.handle.net/2097/35470.
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Doctor of PhilosophyDepartment of Chemistry
Duy H. Hua
Small molecules are of great importance in drug discovery currently. The first three chapters discussed the design, synthesis and bio-evaluation of three different classes of small molecules and exploration of their biological targets. Triacsin C analogs were designed as long chain fatty acyl-CoA synthetase (ACSL) inhibitors for attenuating ischemia and reperfusion (I/R) injury. Oxadiazole derivatives were designed as T-type calcium channel inhibitors, which have potential application in the treatment of seizure and epilepsy. Tricyclic pyrone derivatives were reported as anti-Alzheimer lead compounds in previous research done by the Hua group. TP70 and CP2 were synthesized to explore their pharmacokinetics properties. Chapter 4 described chiral-substituted poly-N-vinylpyrrolidones (CSPVP) supported Cu/Au nanoclusters mediation of cyclization reaction of 5-substituted nona-1,8-dien-5-ols. A five-member cyclized lactone possessing a stereogenic tetrasubstituted carbon center was formed in a one-step Cu/Au nanoclusters-hydrogen peroxide oxidation reaction. This developed a novel and simple method to synthesize tetrasubstituted carbon stereogenic center. Drawbacks of the method in my initial study were low reaction yield and moderate enantioselectivity. The chemical yield and enantioselectivity have been significantly improved by introducing bulkier substitution in C3 and C4 positions of CSPVP according to the updates of ongoing research.
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Lacovig, Paolo. « Electronic structure, morphology and chemical reactivity of nanoclusters and low-dimensional systems : fast photoemission spectroscopy studies ». Doctoral thesis, Università degli studi di Trieste, 2010. http://hdl.handle.net/10077/3685.
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2008/2009L'obiettivo di questa tesi è l'applicazione della spettroscopia di fotoemissione allo studio di nanoparticelle supportate e di sistemi a bassa dimensionalità. Ad una primo periodo dedicato allo sviluppo del rivelatore e del software per un nuovo analizzatore d'energia per elettroni installato presso la linea di luce SuperESCA ad Elettra, è seguita una fase durante la quale ho eseguito una serie di esperimenti mirati ad esplorare le potenzialità del nuovo apparato sperimentale. Il primo risultato ottenuto riguarda la comprensione della relazione che intercorre tra le variazioni della reattività chimica del sistema Pd/Ru(0001) e il numero degli strati di Pd cresciuti in modo pseudomorfico sul substrato di rutenio. La risoluzione temporale raggiunta con la nuova strumentazione ci ha permesso di studiare processi dinamici su una scala temporale fino ad ora inaccessibile per la spettroscopia di fotoemissione dai livelli di core: in particolare abbiamo studiato la crescita del grafene ad alta temperatura sulla superficie (111) dell'iridio e la reattività chimica di nanocluster di Pt supportati su MgO. Nel primo caso abbiamo messo in evidenza come la formazione del grafene proceda attraverso la nucleazione di nano-isole di carbonio che assumono una peculiare forma di cupola. Nel secondo caso siamo riusciti a seguire sia la dinamica del processo di adsorbimento di CO, sia la reazione CO + 1/2 O2 -> CO2 sulle nanoparticelle di Pt depositate su un film ultra-sottile di ossido di magnesio. Infine, abbiamo caratterizzato la morfologia di nanoparticelle di Pd, Pt, Rh e Au cresciute su diversi substrati a base di carbonio, in particolare grafite, nanotubi a parete singola e grafene. Tra i vari risultati abbiamo compreso come l'interazione metallo-substrato dipenda dalla dimensione delle nano-particelle e abbiamo evidenziato il ruolo centrale dei difetti del substrato nei processi di nucleazione e intercalazione.
The objective of this thesis is the application of photoelectron spectroscopy for the investigation of supported nanoclusters and low-dimensional systems. After a first stage devoted to the development of the detector and the software for the electron energy analyser installed on the SuperESCA beamline at Elettra, during the PhD project I've performed a series of experiments aimed to explore the capabilities of the new experimental apparatus. One of the first results concerns the understanding of the relation between the modifications in the chemical reactivity of the Pd/Ru(0001) system and the thickness of the pseudomorphically grown Pd overlayer. The temporal resolution achieved with the new experimental set-up allowed us to study dynamical processes on a new time scale, in particular the graphene growth process at high temperature on the Ir(111) surface and the chemical reactivity of Pt nanoclusters supported on MgO. In the former case, we discovered that graphene formation proceeds via preliminary nucleation of dome-shaped C nano-islands. In the second case, we succeded in following both the dynamics of CO adsorption process and the CO + 1/2 O2 -> CO2 reaction on Pt nanoclusters grown on a ultra-thin film of magnesium oxide. Finally, the morphology of Pd, Pt, Rh and Au nanoclusers grown on different carbon-based substrates (namely graphite, single-walled carbon nanotubes and graphene) has been characterized. Among the results we report the understanding of the dependence of the metal-substrate interaction on the cluster size and the role of defects in the nucleation and intercalation processes.
XXII Ciclo
1972
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PRADA, STEFANO. « Enhancing oxide surface reactivity by doping or nano-structuring ». Doctoral thesis, Università degli Studi di Milano-Bicocca, 2014. http://hdl.handle.net/10281/50011.
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Wide band-gap simple oxides are rather inert materials, which found applications in heterogeneous catalysis mainly as supports for active metal nanoparticles. This thesis investigates tailored modifications of the oxide characteristics aimed at making these substrates more reactive in catalytic processes. In particular we are interested in engineering the charge transfer with supported metal catalysts in order to enhance their activity and selectivity. By using first principles calculations in the framework of the density functional theory, we have explored two main routes in this field: 1) nanostructuring, in particular nanothick oxide films supported on metals, and 2) doping of oxides with substitutional metal ions. After addressing methodological aspects related to the theoretical simulations of these materials, we have considered the role of oxide doping in optimizing the structural and electronic properties of supported gold adparticles; we have shown that depending on the dopant and the nature of the oxide it is possible to finely tune the shape and the charge state of adsorbed metal particle. Moreover we have combined oxide doping and nanostructuring in modifying the work function of metal substrates. By varying parameters like nature, position, and concentration of dopants within the metal-supported oxide films, it is possible in principle to modify the work function of the metallic support in a desired way.
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Dessal, Caroline. « Influence de l'atmosphère réactive sur la stabilité structurale de catalyseurs Pt1 supporté et performances associées en oxydation de CO et photogénération d'hydrogène ». Thesis, Lyon, 2018. http://www.theses.fr/2018LYSE1305/document.
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Ce travail de thèse a consisté en l’étude de catalyseurs ultradispersés, composés de clusters nanométriques ou d’atomes isolés (single-atom catalysts, SACs) de métal, une nouvelle classe de catalyseurs faisant actuellement l’objet d’un engouement mondial. Les systèmes Pt/?-Al2O3 et Pt/TiO2 ont été préparés, caractérisés et testés en oxydation de CO et photogénération d’hydrogène, respectivement. Plusieurs méthodes d’imprégnation et de traitement thermique ont été comparées, notamment grâce à l’analyse de la dispersion du platine par microscopie électronique en transmission à balayage (STEM). Pour la préparation de SACs, notre choix s’est finalement porté sur l’imprégnation à humidité naissante d’une faible charge de précurseur Pt(NH3)4(NO3)2, suivie d’une calcination à l’air. L’étude des performances catalytiques et de l’évolution structurale des catalyseurs au cours des réactions a permis de montrer que les atomes isolés (cations) de platine étaient moins actifs que les clusters (réduits) pour les deux systèmes catalytiques étudiés. Dans le cas de Pt/?-Al2O3, des suivis par spectroscopie d’absorption X (XAS) operando en rayonnement synchrotron, spectroscopie infrarouge par réflexion diffuse (DRIFTS) operando et microscopie environnementale (E-STEM) ont montré la formation et la déstabilisation des SACs, cette dernière étant toutefois moindre en conditions oxydantes. En effet, l’oxygène stabilise le platine isolé via la formation de plusieurs liaisons Pt-O-Al comme montré par modélisation DFT, alors que la présence d’un composé réducteur (CO, H2) conduit à la formation de clusters, mobiles sur leur support. Ce travail met en évidence les limites possibles concernant la stabilisation et la mise en œuvre des SACs dans des réactions catalytiques impliquant des conditions réductricesThis PhD work is focused on the study of ultradispersed catalysts, composed of nanometer-sized clusters or isolated atoms (single-atom catalysts, SACs) of metal, a new class of catalysts which are currently the object of worldwide interest. The Pt/?-Al2O3 and Pt/TiO2 systems were prepared, characterized and evaluated for CO oxidation and hydrogen photogeneration, respectively.Several methods of impregnation and thermal treatment were compared, in particular through platinum dispersion analysis using scanning electron microscopy (STEM). For the preparation of SACs, our choice finally turned to the incipient wetness impregnation of Pt(NH3)4(NO3)2 precursor at low loading, followed by calcination in air.For the two catalytic systems of interest, the study of the performances and the structural evolution of the catalysts during the reactions shows that isolated Pt atoms (cations) are less active than their (reduced) cluster counterparts.In the case of Pt/?-Al2O3, operando X-ray absorption spectroscopy (XAS) using synchrotron radiation, operando diffuse reflectance infrared spectroscopy (DRIFTS), and environmental microscopy (E-STEM) allowed us to monitor the SAC formation and destabilization, the latter being however limited in oxidizing conditions. Indeed, the presence of oxygen stabilizes single Pt atoms via the formation of several Pt-O-Al bonds as shown by DFT modeling, whereas the presence of a reducing compound (CO, H2) leads to the formation of Pt clusters, mobile on their support.This work highlights the possible limitations in the stabilization and implementation of SACs for catalytic reactions involving reducing conditions
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Gotterbarm, Karin [Verfasser], et Hans-Peter [Akademischer Betreuer] Steinrück. « Model Catalysis – Single Crystal Surfaces and Graphene-Supported Metal Nanocluster Arrays Studied by In Situ High Resolution XPS / Karin Gotterbarm. Gutachter : Hans-Peter Steinrück ». Erlangen : Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 2015. http://d-nb.info/1076166555/34.
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Chou, Chung-Pin, et 周崇斌. « Supported Cobalt Nanoclusters on an Insulating Si3N4 Film ». Thesis, 2002. http://ndltd.ncl.edu.tw/handle/54312046120257857482.
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碩士國立清華大學
物理學系
90
In this study, a novel phenomenon of forming monodispersed Co nanoparticles at room temperature on a single-crystal Si3N4 dielectric thin film is presented. Results of very narrow size distributions with an average size of ~30 Co atoms have been obtained. We have found that cobalt clusters deposited on Si3N4 are stable with respect to cluster agglomeration/coalescence and thermal decomposition. Also, we have confirmed that the average size of Co clusters is independent of the deposition time and insensitive to the magnitude of the deposition flux. Therefore, their areal density can be controlled by the deposition time. The motivation for using a single-crystal Si3N4 support is two-fold. First, the dielectric support reduces chemical intermixing and electronic coupling (Si3N4 is an excellent diffusion barrier with a bandgap energy of 4-5 eV) between metal clusters and the substrate compared with situations using semiconductor or metal surfaces. Second, the defect-free Si3N4 surface provides us a unique opportunity to study the formation of metal clusters without the influence of surface defects. Consequently, quantum effect can play an important role in the size control.
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Shiu, Hung-wei, et 許紘瑋. « Catalytic properties of Au nanoclusters supported on Al2O3/NiAl (100) surface ». Thesis, 2006. http://ndltd.ncl.edu.tw/handle/82083431818454577809.
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碩士國立中央大學
物理研究所
95
We have studied the adsorption and decomposition of methanol on well-defined supported Au nanoclusters as a model catalyst by using synchrotron-based high-resolution photoemission spectroscopy (PES). Au nanoclusters are deposited on well-ordered Al2O3 film grown on NiAl (100) through vapor deposition in the ultrahigh vacuum conditions (＜3 x 10-10 torr) at 300 K, 450 K, and 570 K. Gold nanoclusters are studied by using both PES and scanning tunneling microscopy (STM). Form STM images, Au atoms nucleated on crystalline Al2O3 films as nanoclusters and the average size of Au nanoclusters is slightly increased at the deposition temperature of 450 K. However, at 570 K deposition temperature sudden change in the average size of Au nanoclusters is observed, which is probably due to higher diffusion coefficient. To study methanol decomposition, methanol was adsorbed on Au/Al2O3/NiAl (100) at 120 K and subsequently annealed to different temperatures. In our annealing experiment we observe that the methanol C1s peak shifts toward lower binding energy with annealing temperature, which indicates more than one intermediate C-species before it decomposes to CO. We also found the activity for methanol decomposition is highly dependent on the structure of supported Au catalyst. After annealing to 310 K, a sudden shift for C1s peaks may imply that C-O scission and reforming to another hydrocarbon species.
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Pillay, Devina. « Growth, structure, and chemistry of 1B metal nanoclusters supported on TiO₂(110) ». Thesis, 2006. http://hdl.handle.net/2152/2791.
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Stiehl, James Daniel. « Model catalyst studies of the CO oxidation reaction on Titania supported gold nanoclusters ». Thesis, 2004. http://hdl.handle.net/2152/1416.
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Stiehl, James Daniel Mullins Charles Buddie. « Model catalyst studies of the CO oxidation reaction on Titania supported gold nanoclusters ». 2004. http://repositories.lib.utexas.edu/bitstream/handle/2152/1416/stiehlj71428.pdf.
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Ye, Yi Jen, et 葉宜貞. « Study on self-organized monodispersion of supported Iron nanoclusters on Si3N4(0001)/Si(111) ». Thesis, 2003. http://ndltd.ncl.edu.tw/handle/69207394196312418998.
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碩士國立清華大學
物理學系
91
In this thesis, we report the self-organized formation of monodispersed Fe, Ni, and Co nanoclusters on a single-crystal Si3N4 dielectric thin film at room temperature. Fe, Ni, and Co nanoclusters display size-limiting monodispersion behavior and have a very narrow size distribution. We have confirmed that the average sizes of Fe, Ni, and Co nanoclusters are independent of the adatom coverage and the areal density of the clusters is linearly proportional to the deposition coverage. We have also concluded that the atomic number distribution of Fe nanoclusters deduced from the experimental result is consistent with the new nucleation model proposed by us. In this model, this novel phenomenon of self-limiting size distribution originates from the large surface free energy and the quantum size effect of the metal nanoclusters in the ultrasmall size regime. Further, according to the pair distribution function, we found that no correlation relationship exists or mutual interactions among the Fe nanoclusters.
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Wu, Yu-Cheng, et 武昱成. « Decomposition of methanol on vanadium nanoclusters supported by graphene/Ru(0001) and Al2O3/NiAl(100) ». Thesis, 2018. http://ndltd.ncl.edu.tw/handle/f2at56.
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碩士國立中央大學
物理學系
106
The catalytic decomposition of methanol (CH3OH) is extensively investigated because the principal reaction is applied in direct methanol fuel cells (DMFC), which offer a prospect of efficient conversion of methanol to electricity, and because it can serve as a source of hydrogen. As the performance of DMFC or the production of hydrogen is governed largely by the catalyzed reaction, a knowledge of the detailed reaction kinetics and a correlation between reactivity and structure of the catalysts are desirable. To respond to the demand, we investigated the adsorption and reaction of methanol-d4 (CD3OD) on vanadium (V) nanocluster supported on graphene grown on Ru(0001) single crystal and θ-Al2O3/NiAl(100), under ultrahigh vacuum conditions and with infrared reflection absorption spectroscopy and temperature programmed desorption. TPD results shows the distinct desorption of HD, D2 and methane from the surface around 400 K; there is no any CO desorption feature was found indicating CO bond scission along with dehydrogenation. The IRAS results show the C-O bond scission of methanol-d4 or methoxy start around 180 K. From TPD and IRAS results we have two different guess for the methanola-d4 reaction route on the V/Al2O3/NiAl(100). First, on the V surface the O-D bond scission happen and as the temperature reach to 180 K the C-O bond scission of methoxy takes place. The other guess is O-D bond scission after the C-O bond scission, thereafter; all the products dehydrogenated further to atomic oxygen, deuterium and carbon then diffused into V nanoclusters or substrate. For methanol-d4 on the V nanoclusters/graphene/Ru(0001), the TPD spectra show desorption of methanol-d4 only. Further, the vibration of CD3 from the IRAS spectra has a red shift reveal the C-O bond scission of methanol-d4. It seems that methanol-d4 decomposes on the V nanoclusters while all the products diffuse into the substrate.
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Huang, Yi-Cheng, et 黃怡誠. « Oxidative steam reforming of ethanol on rhodium nanoclusters supported by graphene grown on Ru(0001) ». Thesis, 2019. http://ndltd.ncl.edu.tw/handle/deu729.
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碩士國立中央大學
物理學系
107
With rhodium-based catalysts, rhodium nanoclusters supported on graphene grown on Ru(0001) surface, we investigated how oxygen and water play effective roles in the oxidative steam reforming reaction of ethanol, under ultrahigh vacuum conditions and using temperature programmed desorption (TPD), infrared reflection adsorption spectroscopy (IRAS), synchrotron-based photoemission spectroscopy (PES). The result show that the atomic oxygen (O*) on Rh surfaces promoted the decomposition of ethanol and altered the reaction pathway from the one via C-Hβ bond cleavage forming oxametallacycle to that via C-Hα bond cleavage forming acetaldehyde; the alternation high promoted the production of H2 along with the side products of CO, CH4. The reaction pathway shifted to acetate intermediates with higher oxygen content, which suppressed the production of H2 but promoted that of CO2. Water adsorbed molecularly on Rh surface; no water was dissociated and water desorbed below 200 K. In contrast, on atomic oxygen (O*) pre-covered Rh surface, a great fraction of water molecules underwent dissociation into atomic hydrogen and hydroxyl groups (OH*) and desorbed above room temperature 300 K. The OH* on D2O*/O*-Rh clusters surface abstracted H from ethanol, like O* but did not altered the reaction pathway as effectively as O*－ the O2 effect in this aspect is more significant than the H2O one.
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HUANG, YAN-WEN, et 黃彥文. « A STM Study of Growth of Rh and Pt Nanoclusters Supported by Graphene on Pt(111) ». Thesis, 2016. http://ndltd.ncl.edu.tw/handle/ne3fj9.
Texte intégralRésumé :
碩士國立中央大學
物理學系
104
Pt and Rh nanoclusters formed through vapor deposition on the graphene/Pt(111) are studied by scanning tunneling microscopy (STM). We investigate the growth behaviors of Pt and Rh clusters at 300 K and the effect of thermal treatments. We observe that there are three kinds of positions where Pt and Rh clusters formed preferentially on the graphene/Pt(111): step edge, terrace and domain boundary. The size of clusters on the step edge and domain boundary is smaller than that on terrace site, but their cluster density is greater. We observe two kinds of cluster density of Pt and Rh nanoclusters on the graphene surface at several coverages. The graphene films can be classified into two types large and small rotation angle of graphene with respect to Pt(111) substrate. It is reasonable to assume that these two domains could have different properties for the growth of nanoclusters. The studies of Pt clusters formed at 300 K show that at coverage < 0.7 ML, the cluster density and size of Pt clusters increase with the coverage increasing; at coverage > 0.7 ML, the increase rate of size become slowly. After annealing to 450 K, the coverage is almost the same as the original. However, after annealing to 700 K, only 50 % of Pt remained on the graphene. Because of getting thermal energy during annealing, the cluster sizes become smaller and uniform, and density increases obviously. The studies of Rh clusters formed at 300 K show that when the coverage increases, the cluster density increases, but the Rh clusters remain the same size until the coverage is increased to about 0.65 ML. The Rh cluster sizes start to increase when the cluster density become saturated (4.76×1012 cm-2) at coverage > 0.65 ML. After annealing, the Rh clusters become bigger and more uniform in size, but the clustery density decreases.
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Hung, Ting-Chieh, et 洪碇傑. « Methanol Decomposition on Rh Nanoclusters supported by Al2O3/NiAl(100)：A combined IRAS, TPD and PES study ». Thesis, 2014. http://ndltd.ncl.edu.tw/handle/j9s37e.
Texte intégralRésumé :
碩士國立中央大學
物理學系
102
Methanol decomposition on Rh nanoclusters supported by Al2O3/NiAl(100) as a model system is studied by IRAS, TPD and PES. The study contained two parts: surface structures of Rh clusters probe with CO and methanol decomposition on Rh nanoclusters. The Rh nanoclusters are grown from vapor deposition. The IRAS spectra with CO as a probe show that the CO adsorbed on on-top site of Rh nanoclusters; no other site such as bridge or hollow site have been detected. The CO TPD spectra show that CO desorbed with two distinct peaks, one at 430 K, which is observed for CO on Rh single crystal results and the other at about 360 K, which is observed for CO on small Rh clusters. The PES spectra show that the CO dissociation rate ranges between 21 and 55 %, depending on the coverage and hence the size of the clusters. For the clusters annealed to 700 K, the IRAS spectra show the same CO absorption band but the CO TPD spectra show the proportion of low temperature desorption increases. We argue that the desorption temperature depends on the cluster size. Adsorbed methanol was dehydrogenated on the nanoclusters. The dehydrogenation to CO began below 200 K, and some of the CO formed from the dehydrogenated methanol dissociated into atomic carbon. Our PES results confirm that about 21 - 55 % of molecularly adsorbed CO dissociates into atomic carbon, depending on the size of the clusters. The produced CO desorbed above 300 K and D2 from methanol-d4 above 200 K; no intermediate species were detected in the dehydrogenation process. The PES results show the ratio of methanol dissociating into atomic C is about 43.1 ± 2.0 %. This result suggests that the probability of methanol decomposed into CO is about 86.9 ± 4.5 %. Annealing the sample to 700 K does not result in oxidation of the Rh clusters. The ratio of CO TPD desorption intensities from dehydrogenated methanol and molecularly adsorbed CO on the annealed Rh clusters is greater than that on the pristine Rh clusters. For 1 ML Rh, the ratio increases from 47.2 ± 1 % to 54.4 ± 10 %, and for 4 ML Rh, the ratio increases from 39.9 ± 10 % to 77.9 ± 10 %. The fraction of monolayer methanol undergoing dehydrogenation on the annealed Rh clusters is also greater than that on the pristine Rh clusters. On the annealed 4 ML Rh, the fraction of methanol undergoing dehydrogenation increased to 83.9 % (from 64.9 %), consistent with the result of CO ratio.
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Li, Yu-da, et 李昱達. « Methanol decomposition on Au-Pt bimetallic nanoclusters supported by Al2O3/NiAl(100) : A combined IRAS and TPD study ». Thesis, 2013. http://ndltd.ncl.edu.tw/handle/79077603082467063374.
Texte intégralRésumé :
碩士國立中央大學
物理學系
101
We investigate the surface structures of Au-Pt bimetallic clusters by probe molecule CO and IRAS and TPD. Au and Pt deposited sequentially from vapor onto thin-film Al2O3/NiAl(100) at 300 K form preferentially Au-Pt intermixed bimetallic nanoclusters, despite the order of the metal deposition. For the deposition of Pt followed by Au, the deposited Au atoms prefer to decorate the edges of Pt clusters (low coordination sites) and aggregates with the following deposited Au; the 2 ML Au deposited cover only a small portion of the Pt cluster surface. For the reverse order of deposition, the deposited Pt atoms have no preferential sites and cover the Au cluster easily, but there are still few isolated Au atoms on the surface. The enhancement of infrared absorption for CO on Au sites of Au-Pt bimetallic cluster was observed. The effect indicates that the cluster surface consists of both Au and Pt atoms and the surface Au is not only coordinated to Pt but is also preferentially low coordinated. Methanol decomposition on Au-Pt bimetallic nanoclusters supported by Al2O3/NiAl(100) is studied by IRAS and TPD. Two decomposition channels are observed for methanol adsorbed on Au-Pt bimetallic nanoclusters: dehydrogenation to CO and C-O bond scission. The produced CO and D2 from methanol dehydrogenation increased in proportion to the Pt sites on the surface of Au-Pt bimetallic clusters, but the varied Pt sites of the surface change little probability of C-O bond scission. Comparing the desorption of molecularly adsorbed CO to CO from methanol decomposition on Au-Pt bimetallic clusters, we found that the produced CO amounts to about 70 - 80 % of CO saturating the clusters, smaller than that (above 90 %) on pure Pt clusters. It indicates that the productivity, number of CO produced per surface Pt sites, is smaller than that on pure Pt clusters. The pre-adsorbed CO can not prohibit entirely the dehydrogenation and the C-O bond scission of methanol, but decrease the probability of these reactions. The unblocked sites, such as bridge and hollow sites, are still reactive. The effect of alloying Pt with Au to reduce the effect CO poison is insignificant; the probability of methanol decomposition on CO-poisoned Au-Pt bimetallic clusters is similar to that on CO-poisoned pure Pt clusters.
20
Cai, Pei-Yang, et 蔡佩仰. « Methanol Decomposition on Pt nanoclusters supported by Graphene on Pt(111)：A combined RHEED, IRAS and TPD study ». Thesis, 2016. http://ndltd.ncl.edu.tw/handle/mdugnc.
Texte intégralRésumé :
碩士國立中央大學
物理學系
104
The Pt nanoclusters grown from vapor deposition on single layer graphene have been studied by reflection high energy electron diffraction (RHEED). The results show that the Pt nanoclusters are highly crystalline and their structures and lattice constant are significantly affected by the graphene/Pt(111) substrate. Structural analysis based on the RHEED patterns indicates that graphene grow with varied orientations but two are primary: graphene[1000]//Pt(111)[11-2] and graphene[1-100]//Pt(111)[11-2]. Pt nanoclusters grew as fcc phase, with their (111) facets parallel to the graphene surface and with varied orientations with respect to graphene/Pt(111); the primary one has its [11-2] direction parallel to [11-2] direction of Pt(111), denoted as Pt(111) clusters [11-2]//Pt(111)[11-2]. The clusters grew with two kinds. Their orientations differ by 60˚ from each other. Since fcc Pt clusters in (111) orientation has six-fold symmetry, the two kinds of clusters are at the same orientation with respect to the substrate. The lattice constant of the Pt nanoclusters is expanded only in surface normal direction (4.02 – 4.34 Å), relative to that of fcc bulk Pt (3.92 Å). The lattice constant decreases with the coverages, but indenpent of annealing temperature. Methanol decomposition on Pt nanoclusters supported by graphene as a model system is studied by IRAS and TPD. The study contained two parts: surface structures of Pt clusters probe with CO and methanol decomposition on Pt nanoclusters. The IRAS spectra with CO as a probe show that the CO adsorbed on on-top site of Pt nanoclusters; no other site such as bridge or hollow site have been detected. The CO TPD spectra show that CO desorbed with two distinct peaks, one at 390 K for CO on terrace sites, which is observed for CO on Pt single crystal results and the other at about 470 K for CO on low-coordinated site, which is observed for CO on small Pt clusters. Both IRAS and TPD spectra for methanol experiments show that the monolayer methanol on the clusters compeletly desorb about 136 K, significantly lower than that for methanol desorption from Pt(111) single crystal (170 K) and also that for methanol decomposition on Pt(111) single crystal (200 K). No CO and hydrogen produced from decomposition is detected, indicating that methaol on the Pt nanoclusters on graphene/Pt(111) does not decompose.
21
Lee, Hsuan, et 李璿. « Methanol Decomposition on Au-Rh Bimetallic Nanoclusters supported by Al2O3/NiAl(100) : A combined IRAS and TPD study ». Thesis, 2016. http://ndltd.ncl.edu.tw/handle/4526t2.
Texte intégralRésumé :
碩士國立中央大學
物理學系
104
We probe the surface structure and composition of Au-Rh bimetallic nanoclusters on thin-film Al2O3/NiAl(100) at 300K with molecular CO, temperature programmed desorption (TPD) and infrared reflection absorption spectroscopy (IRAS). For the deposition of Au onto Rh nanoclusters, the numbers of Rh sites decrease linearly with Au deposition. For the metal deposition in the reverse order, Au segregates at the surface and then forms Rh core – Au shell structure. The infrared absorption for CO on Au sites was significantly enhanced with Au deposition. We observed that no CO induces structural change for Au-Rh bimetallic nanoclusters during the CO desorption whereas CO adsorbed on Au sites suppresses the IR absorption of CO on Rh sites, despite the order of the metal deposition. For the investigation of thermal stability, we discovered that in the bimetallic clusters, the Au atoms preferentially covered Rh core at 450 K but both Au and Rh attenuated significantly at 700 K. The decomposition of methanol proceeded through dehydrogenation, primarily on Rh sites of Au-Rh bimetallic nanoclusters. The reactivity of methanol decomposition dramatically decreases for the bimetallic clusters formed by small coverages of Au ( 0.5 ML) deposited onto Rh clusters of large size (1.0 ML) because the Au atoms prefer to occupy the low-coordinated sites of Rh clusters. Nevertheless, the activation energy of methanol decomposition on the bimetallic clusters changes insignificantly. The reactivity of methanol decomposition to CO on small Rh clusters (0.25 ML) does not be change with Au deposition because all the Au atoms occupy the low coordinated Rh sites. The reactivity of methanol decomposition on the bimetallic clusters formed by Rh deposited onto Au clusters gradually attenuates with Rh deposition. The revolution of the reactivity with following Rh deposition is similar to that with Rh deposited on pure Rh clusters.
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Lin, Yan-Ru, et 林讌如. « Superatom-Type Silver Nanoclusters Supported by Dithiophosphates and Templated Galvanic Synthesis of M/Ag (M = Au, Pd, Pt) Alloy Clusters ». Thesis, 2016. http://ndltd.ncl.edu.tw/handle/24v43q.
Texte intégral
23
Wilson, James, et 詹偉森. « Atomic Structures and Reactivity of Rhodium Nanoclusters Supported by Graphene Grown on Pt(111) : A Combined RHEED and XPS Study ». Thesis, 2018. http://ndltd.ncl.edu.tw/handle/xsh547.
Texte intégralRésumé :
碩士國立中央大學
物理學系
106
By means of reflection high energy electron diffraction (RHEED), we examined the atomic structures and orientation of the Rh nanoclusters grown by vapor deposition on graphene/Pt(111). Rh nanoclusters and graphene were grown with varied orientations observed by intensity distribution as a function azimuthal angle. The Rh nanoclusters have one couple of peak dominant, indicate that the Rh nanoclusters grow with one main orientation, differently from graphene, which was found to grow with two main orientations. Rh nanoclusters are grown as FCC phase with their (111) facets parallel to the graphene surface and exhibit an orientation same as that of Pt(111). The lattice constant of Rh nanoclusters found to be stable as a function of coverage and temperature. In order to probe the reactivity of Rh nanostructures, we used XPS to monitor the CO adsorption sites, the process of dissociation, and the formation of atomic C and O. We adsorbed CO at 250 K on 1 ML Rh nanoclusters, and got two peaks of O 1s signal around 533.3 and 532.35 eV. Implying CO adsorbed at two adsorption sites which are top and bridge site. When we annealed to 350 K and 450 K, the intensity of molecular O 1s signal decreased and the production of atomic oxygen appear around 531.2 eV as the effect of CO dissociation. Further annealing to high temperature 550 K all molecular CO desorbed from the surface of Rh nanoclusters. The similar result also found on 2 ML Rh nanoclusters.
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Chang, Chun-Chih, et 張鈞智. « Theoertical Studies of Chemical Reactions on Rhodium Nano Clusters : I. Bond scission of NO over rhodium and nickel small-size clustersII. CO2 dissociation on various structures of rhodium nanoclusters (Rh13) supported on unzipped graphene oxide III. Dehydrogenation of ethane, propane and butane on Rh13 clusters supported on unzipped graphene oxide、IrO2 (110) and TiO2 (110) ». Thesis, 2016. http://ndltd.ncl.edu.tw/handle/84735474505585045774.
Texte intégralRésumé :
博士國立臺灣師範大學
化學系
104
We applied density-functional theory (DFT) to investigate the adsorption and dissociation of NO on Rh19 and Ni19 clusters with a double-icosahedral (DI) structure. The transition structures of the NO dissociating on the potential-energy surfaces were derived with the nudged-elastic-band (NEB) method. The adsorption energies of NO molecules on the rhombus-center region of DI clusters are -2.53 eV and -2.78 eV with the N-O bond elongated to 1.33Å and 1.35 Å, respectively, on Ni19 and Rh19, compared to 1.16 Å of the gaseous NO counterpart. The barriers to the dissociation of N-O on both DI-Rh19 (Ea = 0.24 eV) and DI-Ni19 (Ea = 0.42 eV) clusters are small, indicating that the rhombus-center region of DI metal clusters might activate the scission of the N-O bond. To understand the size effects of the rhodium nanocluster, we first investigated the catalytic activity of various rhodium nanoclusters (Rhn, n = 1, 4, 5, 8, 13 amd 14) on unzipped graphene oxide (Rhn/UGO). The calculated result exhibited that the catalytic activity of CO2 dissociation on Rh13/UGO systems is better than other systems. The catalytic activity of various structures of Rh13 clusters on unzipped graphene oxide (Rh13/UGO) has been further investigated for comparison with Rh13 nanoclusters and Rh(111) surfaces. In, addition, the binding energy of Rh atoms on UGO is less than the cohesive energy (- 5.75 eV) of bulk Rh, indicating that the Rh atoms adsorbed on UGO tend to collect into clusters. We systematically calculated the energies of adsorption of CO2 on Rh13 nanoclusters in various stable shapes on unzipped graphene oxide; Rh13-Ih/UGO had the largest energy (where the Ih representing icosahedral shape), -1.18 eV, with the C–O bond being elongated from 1.17 to 1.29 Å; the barrier for dissociation of CO2 on Rh13-Ih/UGO is, accordingly, the smallest (Ea = 0.45 eV), indicating that Rh13-Ih/UGO might act as an effective catalyst to adsorb and to activate the scission of the C-O bond of CO2 . We finally discussed the adsorption and dehydrogenation of alkanes (CnH2n+2, n = 2, 3, 4) on a low-symmetry Rh13 cluster (Rh13-Ls) in comparing with the system of the same cluster (Rh13-Ls) but supported on either an unzipped graphene-oxide (UGO) sheet (Rh13-Ls/UGO), or an IrO2 (110) surface (Rh13-Ls/IrO2), or TiO2 (110) surface (Rh13-Ls/TiO2) to understand the different support effects between Rh13-Ls and the various supports. The adsorption energies, calculated with density-functional theory, of these alkanes follow the order Rh13-Ls/UGO ≈ Rh13-Ls/ TiO2 > Rh13-Ls > Rh13-Ls/ IrO2. Our proposed reaction path for the dehydrogenation of ethane, propane and butane on Rh13-Ls/UGO has the first barriers of height 0.21, 0.22 and 0.16 eV, respectively, to form -C2H5, -C3H7 and -C4H9. In comparing with the barriers on Rh13-Ls、Rh13-Ls/ TiO2 and Rh13-Ls/ IrO2, we found that the barrier on Rh13-Ls/UGO is the lowest for all alkanes. We also studied the electronic properties, such as charge differences, density of states, electron localization functions and interaction energies, to explain the interaction between adsorbates and substrates, using density-functional theory (DFT).