Download or read book Scanning Tunneling Microscopy Study on Model Platinum Catalysts written by Sangho Lee and published by . This book was released on 1993 with total page 310 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Bridging the Pressure Gap written by and published by . This book was released on 1994 with total page 229 pages. Available in PDF, EPUB and Kindle. Book excerpt: Results of this thesis show that STM measurements can provide information about the surfaces and their adsorbates. Stability of Pt(110) under high pressures of H2, O2, and CO was studied (Chap. 4). In situ UHV and high vacuum experiments were carried out for sulfur on Pt(111) (Chap. 5). STM studies of CO/S/Pt(111) in high CO pressures showed that the Pt substrate undergoes a stacking-fault-domain reconstruction involving periodic transitions from fcc to hcp stacking of top-layer atoms (Chap. 6). In Chap. 7, the stability of propylene on Pt(111) and the decomposition products were studied in situ with the HPSTM. Finally, in Chap. 8, results are presented which show how the Pt tip of the HPSTM was used to locally rehydrogenate and oxidize carbonaceous clusters deposited on the Pt(111) surface; the Pt tip acted as a catalyst after activation by short voltage pulses.
Download or read book Bridging the Pressure Gap written by Brian James McIntyre and published by . This book was released on 1994 with total page 504 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Scanning Tunneling Microscopy Studies on the Structure and Stability of Model Catalysts written by Fan Yang and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: An atomic level understanding of the structure and stability of model catalysts is essential for surface science studies in heterogeneous catalysis. Scanning tunneling microscopy (STM) can operate both in UHV and under realistic pressure conditions with a wide temperature span while providing atomic resolution images. Taking advantage of the ability of STM, our research focuses on 1) investigating the structure and stability of supported Au catalysts, especially under CO oxidation conditions, and 2) synthesizing and characterizing a series of alloy model catalysts for future model catalytic studies. In our study, Au clusters supported on TiO2(110) have been used to model supported Au catalysts. Our STM studies in UHV reveal surface structures of TiO2(110) and show undercoordinated Ti cations play a critical role in the nucleation and stabilization of Au clusters on TiO2(110). Exposing the TiO2(110) surface to water vapor causes the formation of surface hydroxyl groups and subsequently alters the growth kinetics of Au clusters on TiO2(110). STM studies on Au/TiO2(110) during CO oxidation demonstrate the real surface of a working catalyst. Au clusters supported on TiO2(110) sinter rapidly during CO oxidation, but are mostly stable in the single component reactant gas, either CO or O2. The sintering kinetics of supported Au clusters has been measured during CO oxidation and gives an activation energy, which supports the mechanism of CO oxidation induced sintering. CO oxidation was also found to accelerate the surface diffusion of Rh(110). Our results show a direct correlation between the reaction rate of CO oxidation and the diffusion rate of surface metal atoms. Synthesis of alloy model catalysts have also been attempted in our study with their structures successfully characterized. Planar Au-Pd alloy films has been prepared on a Rh(100) surface with surface Au and Pd atoms distinguished by STM. The growth of Au-Ag alloy clusters have been studied by in-situ STM on a cluster-to-cluster basis. Moreover, the atomic structure of a solution-prepared Ru3Sn3 cluster has been resolved on an ultra-thin silica film surface. The atomic structure and adsorption sites of the ultrathin silica film have also been well characterized in our study.
Download or read book Scanning Tunneling Microscopy in Surface Science Nanoscience and Catalysis written by Michael Bowker and published by John Wiley & Sons. This book was released on 2009-11-11 with total page 258 pages. Available in PDF, EPUB and Kindle. Book excerpt: Here, top international authors in the field of STM and surface science present first-class contributions on this hot topic, bringing the reader up to date with the latest developments in this rapidly advancing field. The focus is on the nanoscale, particularly in relation to catalysis, involving developments in our understanding of the nature of the surfaces of oxides and nanoparticulate materials, as well as adsorption, and includes in-situ studies of catalysis on such model materials. Of high interest to practitioners of surface science, nanoscience, STM and catalysis.
Download or read book Low temperature Scanning Tunneling Microscopy Studies on Model Catalyysts written by Maria Kulawik and published by . This book was released on 2006 with total page 124 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Structure and Reactivity of Nanostructured Model Catalysts written by Thorsten Staudt and published by . This book was released on 2012 with total page 84 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Scanning Tunneling Microscopy in Surface Science written by Michael Bowker and published by Wiley-VCH. This book was released on 2010-02-01 with total page 258 pages. Available in PDF, EPUB and Kindle. Book excerpt: Here, top international authors in the field of STM and surface science present first-class contributions on this hot topic, bringing the reader up to date with the latest developments in this rapidly advancing field. The focus is on the nanoscale, particularly in relation to catalysis, involving developments in our understanding of the nature of the surfaces of oxides and nanoparticulate materials, as well as adsorption, and includes in-situ studies of catalysis on such model materials. Of high interest to practitioners of surface science, nanoscience, STM and catalysis.
Download or read book Scanning Tunneling Microscopy Study of Strong Metal support Interaction in Iron Oxide Based Model Catalysts written by Ke Zhang and published by . This book was released on 2018 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Scanning Tunneling Microscopy Study of Model Molybdenum based Catalysts Supported on Highly Oriented Pyrolytic Graphite written by Haryani Permana and published by . This book was released on 1993 with total page 242 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Scanning Tunneling Investigation of Olefin Dehydrogenation on Platinum Single Crystal and Pt al2o3 nial 110 Model Catalysts written by Safa Shakir-Shatnawi Khan and published by . This book was released on 2015 with total page 116 pages. Available in PDF, EPUB and Kindle. Book excerpt: Propylene and butylene thermal dehydrogenation have been studied on Pt(111) single crystal using Scanning Tunneling Microscopy (STM). Propylene and butylene were heated to 1000 K on the Pt single crystal. Both olefins formed uniform sized carbon clusters, with less than a monolayer coverage on the Pt surface. With cycles of continued dosing and heating, particles grew in number but not size. The catalytic activity stopped by the third saturation dose, leaving areas of bare Pt. Carbon clusters generated from the dehydrogenated propylene and butylene were approximately 1 ©5 in height and 12 ©5 in diameter. Propylene and butylene clusters contained an average of 44 and 51 carbon atoms per cluster respectively. The reactions of Pt nanoparticles on Al2O3/NiAl(110) were compared with those on the Pt single crystal. An Al2O3 thin film was formed with similar properties to previous alumina reported in literature. Ethlyene did not adsorb to the clean alumina regardless of dosing temperature. The Pt nanoparticles formed were circular, flat, and uniform in size (13 ©5) and shape, corresponding to approximately 20 atoms. Annealing the Pt particles up to 1100 K did not produce any change in the size or arrangement of the particles. The Pt nanoparticles deposited only onto crystalline Al2O3 surfaces. Ethylene was then dosed onto the Pt. At 1000 K, ethylene deposited only onto the Pt nanoparticles and not onto the oxide layer. The thermally dehydrogenated ethylene covered the Pt nanoparticles and particles grew to a maximum of 20 ©5. Particle density did not increase at an annealing temperature of 1000 K. At 1100 K the density of particles increased and decorated the step edges. Another set of experiments examined the dehydrogenation of ethylenediamine at 300-500 K on Ni(111). The goal of this study was to form cyanogen. The end result was unidentifiable via imaging by STM and cyanogen formation was not observed.
Download or read book Scanning Tunneling Microscopy Studies on Model Systems Relevant for Heterogeneous Catalysis written by Stig Helveg and published by . This book was released on 2000 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Scanning Tunneling Microscopy Studies of Model Systems Relevant to Catalysis written by Ebbe Kruse Vestergaard and published by . This book was released on 2004 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on 1995 with total page 692 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Model Catalysts in Action written by Bastiaan Lambertus Martinus Hendriksen and published by . This book was released on 2003 with total page 165 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Structure Mobility and Composition of Transition Metal Catalyst Surfaces written by Zhongwei Zhu and published by . This book was released on 2013 with total page 133 pages. Available in PDF, EPUB and Kindle. Book excerpt: Surface structure, mobility, and composition of transition metal catalysts were studied by high-pressure scanning tunneling microscopy (HP-STM) and ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) at high gas pressures. HP-STM makes it possible to determine the atomic or molecular rearrangement at catalyst surfaces, particularly at the low-coordinated active surface sites. AP-XPS monitors changes in elemental composition and chemical states of catalysts in response to variations in gas environments. Stepped Pt and Cu single crystals, the hexagonally reconstructed Pt(100) single crystal, and Pt-based bimetallic nanoparticles with controlled size, shape and composition, were employed as the model catalysts for experiments in this thesis. Surface reconstruction at low-coordinated step sites at high gas pressures was first explored on a stepped Pt(557) single crystal surface under O2. At 298 K, 1 Torr of O2 is able to create nanometer-sized clusters that are identified as surface Pt oxide by AP-XPS, which covers the entire Pt(557) surface. On the flat Pt(111) surface under 1 Torr of O2, Pt oxide clusters can form but are mostly accumulated within 2 nm from the steps. The hexagonal oxygen chemisorption pattern is observed on the terraces. At lower pressures such as 10−7 Torr, O2 only adsorbs at the step edges on Pt(557). The majority of the Pt oxide clusters disappear on both Pt(557) and Pt(111) surfaces after O2 is evacuated to the 10−8 Torr range. Quantitative XPS analysis with depth profiles indicates that the Pt oxide formed on Pt(557) is less than 0.6 nm thick and that the Pt oxide concentration at surface together with oxygen coverage varies reversibly with the O2 pressure. The disappearance of Pt oxide clusters upon O2 evacuation is ascribed to reactions of Pt oxide towards H2 and CO in the vacuum background gases. The structure and surface chemistry of the Pt(557) surface was therefore studied under H2-O2 and CO-O2 mixtures. After exposing Pt(557) to approximately 1 Torr of O2 to induce the formation of Pt oxide clusters, H2 was slowly added into the system. Both HP-STM and AP-XPS results show that the Pt oxide coverage decreases with the H2 partial pressure and that all the Pt oxide disappears at H2 partial pressures above 43 mTorr. Pt steps are restored with the removal of Pt oxide clusters. Water is produced in the gas-phase, which co-adsorbs with hydroxyl species on Pt(557). Detailed analysis shows that the consumption of surface Pt oxide is exclusively responsible for the decrease of oxygen coverage on Pt(557). In the coexistence of 1 Torr of CO and 1 Torr of O2, Pt oxide clusters are not observed like under the H2-O2 mixture. Instead, triangular Pt clusters and double-sized terraces induced by CO are observed. Influences of step configuration on the surface restructuring processes were studied on Pt(557) and Pt(332) that differ only in the step orientation. 500 mTorr of CO creates Pt clusters shaped as triangles and parallelograms on Pt(557) and Pt(332), respectively. When 500 mTorr of C2H4 was introduced afterwards, Pt clusters are removed on Pt(332) but preserved on Pt(557). The three-fold hollow sites at the (111) steps enable the Pt(332) surface to accommodate ethylidyne even covered by CO. As a result, kink Pt atoms at the cluster edges are driven to diffuse to form straight steps, so as to admit more ethylidyne at steps. In contrast, Pt(557) has (100) steps on which ethylidyne does not adsorb, therefore keeping the island structure after the introduction of C2H4. When 500 mTorr of C2H4 was added first into the high-pressure cell, a periodic pattern is resolved at step edges on Pt(332). In contrast, some bright species separated by more than 1 nm are observed on Pt(557). Further introducing 500 mTorr of CO does not facilitate the formation of Pt clusters. The structure and mobility under C2H4, H2, and CO were also studied on the Pt(100) surface, whose topmost layer is rearranged into a hexagonal overlayer in vacuum. Under 1 Torr of C2H4, the hexagonal reconstruction is preserved on Pt(100), which is covered by highly mobile adsorbates. Pt atoms on the hexagonal layer can also move as a result of the weakened interaction between the surface layer and the bulk. The mobility is enhanced under 1 Torr of 1:1 C2H4-H2 mixture because the Pt(100)-hex surface is active in ethylene hydrogenation. The surface mobility along with the catalytic reaction is quenched after introducing 3 mTorr of CO. Meanwhile, the hexagonal reconstruction is lifted by the adsorption of CO. At 5 × 10−6 Torr of C2H4, CO from background gases can also adsorb on Pt(100), creating Pt islands that do not revert to the hexagonal surface when the C2H4 pressure was further increased to 1 Torr. In order to understand the effect of substrates on surface reconstruction, the structure of the stepped Cu(557) surface was monitored in equilibrium with high pressures of gases. Cu generally binds to the reducing gases such as CO, H2, and C2H4 weaker than Pt, leading to a lower coverage on Cu than on Pt at the same gas pressure. Accordingly, 12 Torr of CO is required to induce clusters on Cu(557), because higher CO pressures are needed to keep a sufficient amount of CO that can stabilize clusters. At 1 Torr, large terraces with an average width of 23 nm are observed on Cu(557), because of the low diffusion barrier for Cu atoms both on terraces and along the steps. 500 mTorr of H2 results in step coalescence on Cu(557), giving rise to 6 nm wide terraces. C2H4 adsorption at 500 mTorr results in 5 nm large clusters. CO does not change the Cu(557) surface structure while adding into C2H4, but causes the appearance of large terraces while co-adsorbing with H2. Under oxidizing gases, for example 1 Torr of O2, the Cu(557) surface is significantly oxidized, forming thick layers of Cu oxide. Pt-based bimetallic nanoparticle catalysts were also investigated with AP-XPS under reaction conditions to study their surface chemistry. PtFe nanoparticles do not undergo any surface segregation at 298 K when the gas environment changes, but surface Fe atoms are partially reduced under the C2H4-H2 mixture and partially oxidized under O2. Neither does the surface composition of Pt9Co-Co core-shell nanoparticles change while heating under H2 even to 673 K nor do oxidation states. In Pt-Ni systems, at 393 K, Ni is oxidized under O2 and migrates to the surface because Ni is more susceptible to oxidation than Pt. In contrast, when the surface is reduced by H2, Pt segregates to the surface since the surface free energy of Pt is lower. Such segregation does not occur at 353 K owing to the low atomic mobility in lattice.
Download or read book High Pressure Scanning Tunneling Microscopy Studies of Adsorbate Structure and Mobility During Catalytic Reactions written by David Chi-Wai Tang and published by . This book was released on 2005 with total page 562 pages. Available in PDF, EPUB and Kindle. Book excerpt:
