Matching Items (4)
Description
In-situ environmental transmission electron microscopy (ETEM) is a powerful tool for following the evolution of supported metal nanoparticles under different reacting gas conditions at elevated temperatures. The ability to observe the events in real time under reacting gas conditions can provide significant information on the fundamental processes taking place in catalytic materials, from which the performance of the catalyst can be understood. The first part of this dissertation presents the application of in-situ ETEM studies in developing structure-activity relationship in supported metal nanoparticles. In-situ ETEM studies on nanostructures in parallel with ex-situ reactor studies of conversions and selectivities were performed for partial oxidation of methane (POM) to syngas (CO+H2) on Ni/SiO2, Ru/SiO2 and NiRu/SiO2 catalysts. During POM, the gas composition varies along the catalyst bed with increasing temperature. It is important to consider these variations in gas composition in order to design experiments for in-situ ETEM. In-situ ETEM experiments were performed under three different reacting gas conditions. First in the presence of H2, this represents the state of the fresh catalyst for the catalytic reaction. Later in the presence of CH4 and O2 in 2:1 ratio, this is the composition of the reacting gases for the POM reaction and this composition acts as an oxidizing environment. Finally in the presence of CH4, this is the reducing gas. Oxidation and reduction behavior of Ni, Ru and NiRu nanoparticles were followed in an in-situ ETEM under reacting gas conditions and the observations were correlated with the performance of the catalyst for POM. The later part of the dissertation presents a technique for determining the gas compositional analysis inside the in-situ ETEM using electron energy-loss spectroscopy. Techniques were developed to identify the gas composition using both inner-shell and low-loss spectroscopy of EELS. Using EELS, an "operando TEM" technique was successfully developed for detecting the gas phase catalysis inside the ETEM. Overall this research demonstrates the importance of in-situ ETEM studies in understanding the structure-activity relationship in supported-metal catalysts for heterogeneous catalysis application.
ContributorsChenna, Santhosh (Author) / Crozier, Peter A. (Thesis advisor) / Carpenter, Ray (Committee member) / Sieradzki, Karl (Committee member) / Petuskey, William (Committee member) / Arizona State University (Publisher)
Created2011
Description
Operando transmission electron microscopy (TEM) is an extension of in-situ TEM in which the performance of the material being observed is measured simultaneously. This is of great value, since structure-performance relationships lie at the heart of materials science. For catalyst materials, like the SiO2-supported Ru nanoparticles studied, the important performance metric, catalyst activity, is measured inside the microscope by determining the gas composition during imaging. This is accomplished by acquisition of electron energy loss spectra (EELS) of the gas in the environmental TEM while catalysis is taking place. In this work, automated methods for rapidly quantifying low-loss and core-loss EELS of gases were developed. A new sample preparation method was also established to increase catalytic conversion inside a differentially-pumped environmental TEM, and the maximum CO conversion observed was about 80%. A system for mixing gases and delivering them to the environmental TEM was designed and built, and a method for locating and imaging nanoparticles in zone axis orientations while minimizing electron dose rate was determined.
After atomic resolution images of Ru nanoparticles observed during CO oxidation were obtained, the shape and surface structures of these particles was investigated. A Wulff model structure for Ru particles was compared to experimental images both by manually rotating the model, and by automatically determining a matching orientation using cross-correlation of shape signatures. From this analysis, it was determined that most Ru particles are close to Wulff-shaped during CO oxidation. While thick oxide layers were not observed to form on Ru during CO oxidation, thin RuO2 layers on the surface of Ru nanoparticles were imaged with atomic resolution for the first time. The activity of these layers is discussed in the context of the literature on the subject, which has thus far been inconclusive. We conclude that disordered oxidized ruthenium, rather than crystalline RuO2 is the most active species.
After atomic resolution images of Ru nanoparticles observed during CO oxidation were obtained, the shape and surface structures of these particles was investigated. A Wulff model structure for Ru particles was compared to experimental images both by manually rotating the model, and by automatically determining a matching orientation using cross-correlation of shape signatures. From this analysis, it was determined that most Ru particles are close to Wulff-shaped during CO oxidation. While thick oxide layers were not observed to form on Ru during CO oxidation, thin RuO2 layers on the surface of Ru nanoparticles were imaged with atomic resolution for the first time. The activity of these layers is discussed in the context of the literature on the subject, which has thus far been inconclusive. We conclude that disordered oxidized ruthenium, rather than crystalline RuO2 is the most active species.
ContributorsMiller, Benjamin (Author) / Crozier, Peter (Thesis advisor) / Liu, Jingyue (Committee member) / McCartney, Martha (Committee member) / Rez, Peter (Committee member) / Arizona State University (Publisher)
Created2016
Description
Miedema's plot is used to select the Cu/metal barrier for Cu metallization.The Cu/metal barrier system selected should have positive heat of formation (Hf) so that there is no intermixing between the two layers. In this case, Ru is chosen as a potential candidate, and then the barrier properties of sputtered Cu/Ru thin films on thermally grown SiO2 substrates are investigated by Rutherford backscattering spectrometry (RBS), X-ray diffractometry (XRD), and electrical resistivity measurement. The Cu/Ru/SiO2 samples are analyzed prior to and after vacuum annealing at various temperatures of 400, 500, and 600 oC and at different interval of times of 0.5, 1 and 2 hrs for each temperature. Backscattering analysis indicate that both the copper and ruthenium thin films are thermally stable at high temperature of 600 oC, without any interdiffusion and chemical reaction between Cu and Ru thin films. No new phase formation is observed in any of the Cu/Ru/SiO2 samples. The XRD data indicate no new phase formation in any of the annealed Cu/Ru/SiO2 samples and confirmed excellent thermal stability of Cu on Ru layer. The electrical resistivity measurement indicated that the electrical resistivity value of the copper thin films annealed at 400, 500, and 600 oC is essentially constant and the copper films are thermally stable on Ru, no reaction occurs between copper films and Ru the layer. Cu/Ru/SiO2 multilayered thin film samples have been shown to possess good mechanical strength and adhesion between the Cu and Ru layers compared to the Cu/SiO2 thin film samples. The strength evaluation is carried out under static loading conditions such as nanoindentation testing. In this study, evaluation and comparison is donebased on the dynamic deformation behavior of Cu/Ru/SiO2 and Cu/SiO2 samples under scratch loading condition as a measure of tribological properties. Finally, the deformation behavior under static and dynamic loading conditions is understood using the scanning electron microscope (SEM) and the focused ionbeam imaging microscope (FIB) for topographical and cross-sectional imaging respectively.
ContributorsVenkatesh, Srilakshmi Hosadurga (Author) / Alford, Terry L. (Thesis advisor) / Krause, Stephen (Committee member) / Theodore, David (Committee member) / Arizona State University (Publisher)
Created2010
Description
2,2’ bipyridine (Bpy) can form metal complexes with divalent metals in the form of [M(Bpy-ala)¬3]+2 where M is any divalent metal. These [M(Bpy-ala)¬3]+2 complexes can have very interesting photochemical and redox potentials that can be useful in more complex systems. The use of (2,2′-bipyridin-5yl)alanine (Bpy-ala) as a Noncanonical Amino Acid (NCAA) has allowed Bpy to be incorporated into an amino acid sequence which can now function in a protein scaffold. Previous studies have utilized that power of Bpy-ala to design a protein that can assemble a homotrimeric protein complex in the presence of a divalent metal. However, the issue with this design was that when the homotrimer was formed and the divalent was removed, the protein complex would not dissemble indicating that it was not metal dependent. Point mutations were made to disrupt the protein-protein interactions to favor disassembly in the absence of a divalent metal. Successfully, a mutation was made that allowed the designed protein to be metal dependent for self-assembly. Nevertheless, an issue with this design is that it poorly incorporated ruthenium(II) into the tris Bpy complex forming [Ru(Bpy-ala)¬3]+2, which was one of the main goals of the original design. This thesis sets out to form TRI 05 I13S M6I which should uphold the same metal-dependence as its predecessor and should combine ruthenium (II) into the protein complex forming [Ru(Bpy-ala)¬3]+2. The thesis shows the success of formation and expression of TRI 05 I13S M6I in Escherichia coli cells. This thesis also reports several purification steps and procedures to not only purify TRI 05 I13S M6I but also removing both the His-tag sequence and Fe(II) from the protein. The thesis also shows that TRI 05 I13S M6I does not behave like its predecessor in that it is not metal dependent for self-assembly. While this may be true, this paper also reports the incorporation of ruthenium (II) in the protein structure. Though this may be the first time that ruthenium (II) has been recorded to be in the TRI 05 protein complex with a significant signal, it is still nowhere near the optimal fluorescence that small molecule Bpy can achieve by itself. The thesis reports potential conditions and a plan of attack that should drive this project forward into achieving an optimal signal of the [Ru(Bpy-ala)¬3]+2 complex in a TRI 05 protein scaffold.
ContributorsGrisingher, Dominic Waldo (Author) / Mills, Jeremy (Thesis director) / Nannenga, Brent (Committee member) / Lefler, Scott (Committee member) / School of Molecular Sciences (Contributor, Contributor) / Barrett, The Honors College (Contributor)
Created2019-05