Download or read book Zeolite Y and MgO supported Molecular Metal Complexes and Clusters written by Alper Uzun and published by . This book was released on 2009 with total page 722 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Zeolite and MgO supported Metal Complexes and Clusters written by Ceren Aydin and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: In a search for a fundamental understanding of supported catalysts, supported metal catalysts with essentially molecular structures were synthesized by anchoring organometallic precursors with well-defined structures to uniform and highly crystalline supports. The supports include zeolite NaY, zeolite HSSZ-53 and MgO. The metals include osmium, iridium, and gold, and the corresponding precursors were Os3(CO)12, Ir(C2H4)2(acac), Ir(CO)2(acac), and Au(CH3)2(acac). Characterization of the supported species at the atomic scale was carried out by X-ray absorption (XAS) and infrared (IR) spectroscopies used in tandem with aberration-corrected scanning transmission electron microscopy (STEM). The transformations of these species were tracked, with the data taken under (a) working conditions of a catalyst (during a reaction), (b) in the presence of a reactive atmosphere, or (c) under the influence of the electron beam in the STEM. Time-resolved spectra and images demonstrate the structural changes in the catalysts involving the nuclearity of the metal species, the metal-ligand and metal-support interactions. Fully resolved structures were correlated with catalytic activity for ethylene hydrogenation and CO oxidation reactions. Influence of channel confinement and cage dimensions of a zeolite on cluster formation were investigated starting with Ir1 species. First steps of cluster formation giving Ir2 and Ir3 were tracked in 1D channels of zeolite HSSZ-53 and formation of Ir6 species in 3D supercages of zeolite NaY was examined. Moreover, last steps of cluster growth were revealed by the discovery a sinter-resistant catalyst with a critical diameter of ~1 nm (Ir~40). Characterization with single atom sensitivity help pinpoint atomically dispersed gold catalytic sites on zeolite NaY during CO oxidation and site-isolated Os(CO)2 species formed by fragmentation of Os3 carbonyls on MgO surface. The results show how fundamental understanding can guide the design of catalysts incorporating metal atoms in nanoscale spaces or on surfaces and help unravel the transport of metal atoms and characterize the bonding sites for catalytic species.
Download or read book Supported Molecular Rhodium Complexes and Dimers written by Dicle Yardimci and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Solid catalysts incorporating transition metals are important in industry, providing cost- effective syntheses, ease of separation from products, and control of selectivity. The metal is often expensive and thus often constitutes only about one percent of the catalyst mass, being highly dispersed on a high-area support. Dispersed metals in industrial catalysts are usually highly nonuniform in structure and challenging to characterize, and consequently relationships between structure and catalyst performance are typically less than fully understood. Our approach to the investigation of supported metal catalysts involves the synthesis of uniform catalytic sites that have essentially molecular character. Supported molecular catalysts can be characterized spectroscopically to provide fundamental understanding of the catalyst structure under reactive atmospheres, and thereby determination of structural changes of working catalysts that can be correlated with the catalytic activity and selectivity. The sample characterization techniques used in this work included infrared (IR), extended X-ray absorption fine structure (EXAFS), and X-ray absorption near edge structure (XANES) spectroscopies, as well as gas chromatography (GC) and mass spectrometry (MS) to characterize reaction products. The catalysts were prepared from the organometallic precursor Rh(C2H4)2(C5H7O2) and the supports MgO and zeolite HY. These catalysts initially incorporated site-isolated, mononuclear rhodium complexes on the supports. The complexes on MgO were treated in H2 at elevated temperatures to form the smallest supported rhodium clusters--rhodium dimers. These catalysts are essentially molecular in character and allowed tailoring of the rhodium nuclearity, the ligands bonded to the rhodium, and the rhodium-support interface. The catalysts incorporated mononuclear Rh(C2H4)2 and Rh(CO)2 complexes; dimeric rhodium clusters with ethyl ligands, and dimeric rhodium clusters with CO ligands. These were tested for the hydrogenation of ethylene. Rhodium in various forms is highly active for catalytic hydrogenation of olefins. However, rhodium has been little investigated for diene hydrogenation, because, like other noble metals in the form of supported clusters or particles, it is unselective. We postulated that new catalytic chemistry of rhodium could emerge if the catalytic species were essentially molecular so that they could be tuned by the choice of the rhodium nuclearity and ligands. Thus, we investigated the influence of the following catalyst design variables on the activity and selectivity of supported rhodium for 1,3-butadiene hydrogenation: (a) the metal nuclearity, ranging from one to several; (b) the electron-donor properties of the support (MgO vs. zeolite Y); and (c) other ligands on the rhodium, including reactive hydrocarbons (ethylene or ethyl) and CO. The data show that extremely small MgO-supported rhodium clusters that are partially carbonylated are highly active and selective for the hydrogenation of 1,3-butadiene to give n-butenes. The support, the rhodium nuclearity, and the ligands on rhodium are crucial to the catalyst selectivity, transforming a metal that is typically regarded as unselective for 1,3-butadiene hydrogenation into one that is highly selective even at high conversions. Transition metals in complexes and clusters tend to aggregate to form of more stable, bulk particles under reactive atmospheres, causing catalyst deactivation. We investigated the initial steps of the aggregation of supported metal species that were highly dispersed on MgO and zeolite HY, synthesizing samples that incorporated supported rhodium complexes bonded to ligands with different reactivities (including the support), and then spectroscopically investigated the formation of extremely small rhodium clusters in the presence of H2. The stability of the rhodium complexes and the stoichiometry of the surface-mediated transformations are regulated by the support and the other ligands bonded to the rhodium, being prompted at a lower temperature with zeolite HY than the better electron-donor MgO when the rhodium complexes incorporate ethylene ligands, but occurring more facilely on the MgO than on the zeolite when the ligands are CO. The preparation of highly uniform rhodium dimers is possible. We infer that results such as those presented here may be useful in guiding the design of stable, highly dispersed supported metal catalysts by choice of the support and other ligands on the metal.
Download or read book Supported Molecular Gold Complexes and Clusters written by Javier Guzman and published by . This book was released on 2003 with total page 526 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Inclusion Chemistry with Zeolites Nanoscale Materials by Design written by N. Herron and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 353 pages. Available in PDF, EPUB and Kindle. Book excerpt: Zeolites, with their crystalline microporous structures, are cordial hosts to a wide variety of guests. However, it was the abrupt and unexpected departure of one of these guests (water) from a host (stilbite) on heating which led Cronstedt, in 1756, to coin the term "zeolite" (from the Greek meaning "boiling stone") to describe this material. Since that time, approximately 40 different naturally-occurring zeolites have been discovered on earth. Recent studies of meteorite compositions have shown that these guest-host materials (e. g. , sodalite) occur in other parts of the universe as well. However, it wasn't until the twentieth century that synthetic routes to zeolites and other non-aluminosilicate molecular sieves were discovered. In addition, with the development of X-ray diffraction and the various spectroscopies, better understanding of the nature of the cavities, cages, and channels of these materials has led to the industrial exploitation of their guest-host properties. The world of zeolites has now expanded into a greater than 2 billion pound per year business, with major applications in detergent formulations, catalysis, and as adsorbents and desiccants. Their economic impact is difficult to determine; however, the improvement in gasoline yields alone (from catalytic cracking) must account for hundreds ofbillions ofdollars in increased GDP. In this volume, we have brought together a sampling of recent developments in various areas of guest-host or inclusion chemistry in zeolites.
Download or read book Supported Molecular Rhodium Complexes and Clusters written by Ann Jia-Bao Liang and published by . This book was released on 2008 with total page 754 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Bridging the Gaps in Catalysis written by Bryan Anthony Enderle and published by . This book was released on 2002 with total page 502 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Model Systems in Catalysis written by Robert Rioux and published by Springer Science & Business Media. This book was released on 2009-11-11 with total page 531 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book is an excellent compilation of cutting-edge research in heterogeneous catalysis and related disciplines – surface science, organometallic catalysis, and enzymatic catalysis. In 23 chapters by noted experts, the volume demonstrates varied approaches using model systems and their successes in understanding aspects of heterogeneous catalysis, both metal- and metal oxide-based catalysis in extended single crystal and nanostructured catalytic materials. To truly appreciate the astounding advances of modern heterogeneous catalysis, let us first consider the subject from a historical perspective. Heterogeneous catalysis had its beginnings in England and France with the work of scientists such as Humphrey Davy (1778–1829), Michael Faraday (1791–1867), and Paul Sabatier (1854–1941). Sabatier postulated that surface compounds, si- lar to those familiar in bulk to chemists, were the intermediate species leading to catalytic products. Sabatier proposed, for example, that NiH moieties on a Ni sur- 2 face were able to hydrogenate ethylene, whereas NiH was not. In the USA, Irving Langmuir concluded just the opposite, namely, that chemisorbed surface species are chemically bound to surfaces and are unlike known molecules. These chemisorbed species were the active participants in catalysis. The equilibrium between gas-phase molecules and adsorbed chemisorbed species (yielding an adsorption isotherm) produced a monolayer by simple site-filling kinetics.
Download or read book X Ray Absorption and X Ray Emission Spectroscopy written by Jeroen A. van Bokhoven and published by John Wiley & Sons. This book was released on 2016-03-21 with total page 940 pages. Available in PDF, EPUB and Kindle. Book excerpt: During the last two decades, remarkable and often spectacular progress has been made in the methodological and instrumental aspects of x–ray absorption and emission spectroscopy. This progress includes considerable technological improvements in the design and production of detectors especially with the development and expansion of large-scale synchrotron reactors All this has resulted in improved analytical performance and new applications, as well as in the perspective of a dramatic enhancement in the potential of x–ray based analysis techniques for the near future. This comprehensive two-volume treatise features articles that explain the phenomena and describe examples of X–ray absorption and emission applications in several fields, including chemistry, biochemistry, catalysis, amorphous and liquid systems, synchrotron radiation, and surface phenomena. Contributors explain the underlying theory, how to set up X–ray absorption experiments, and how to analyze the details of the resulting spectra. X-Ray Absorption and X-ray Emission Spectroscopy: Theory and Applications: Combines the theory, instrumentation and applications of x-ray absorption and emission spectroscopies which offer unique diagnostics to study almost any object in the Universe. Is the go-to reference book in the subject for all researchers across multi-disciplines since intense beams from modern sources have revolutionized x-ray science in recent years Is relevant to students, postdocurates and researchers working on x-rays and related synchrotron sources and applications in materials, physics, medicine, environment/geology, and biomedical materials
Download or read book Metal Metal Bonds and Clusters in Chemistry and Catalysis written by John P. Fackler Jr. and published by Springer Science & Business Media. This book was released on 2013-11-22 with total page 344 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book contains a series of papers and abstracts from the 7th Industry-University Cooperative Chemistry Program symposium held in the spring of 1989 at Texas A&M University. The symposium was larger than previous IUCCP symposia since it also celebrated the 25 years that had elapsed since the initial discovery by F. A. Cotton and his co-workers of the existence of metal-metal quadruple bonds. Cotton's discovery demonstrated that multiple bonding in inorganic systems is not governed by the same constraints observed in organic chemistry regarding s and p orbital involvement. The d orbitals are involved in the multiple bonding description. The quadruple bond involves considerable d orbital overlap between adjacent metal centers. Part I of this series of papers focuses upon the impact of this discovery and describes further contributions to the development of the field. Multiple metal-metal bonding now is known to permeate broad areas of transition metal chemistry. The understanding of metal-metal bonding that developed as a result of the discovery of multiple metal-metal bonding awakened a new chemistry involving metal clusters. Clusters were defined by Cotton to be species containing metal-metal bonding. Clusters in catalysis therefore seemed a logical grouping of papers in this symposium. Clusters play an every increasing role in the control of chemical reactions. Part II of this book describes some of the interesting new developments in this field. In Part III the papers examine the role clusters play in describing and understanding solid state materials.
Download or read book Zeolite supported Molecular Complexes of Ruthenium and of Rhodium written by Isao Ogino and published by . This book was released on 2010 with total page 640 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Molecular Rhodium Clusters and Platinum rhodium Bimetallic Clusters on MgO and in Faujasites written by William A. Weber and published by . This book was released on 1998 with total page 842 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Advances in Organic Synthesis written by Atta -ur- Rahman and published by Bentham Science Publishers. This book was released on 2017-09-07 with total page 284 pages. Available in PDF, EPUB and Kindle. Book excerpt: Advances in Organic Synthesis is a book series devoted to the latest advances in synthetic approaches towards challenging structures. It presents comprehensive articles written by eminent authorities on different synthetic approaches to selected target molecules and new methods developed to achieve specific synthetic transformations. Contributions are written by eminent scientists and each volume is edited by an authority in the field. Advances in Organic Synthesis is essential for all organic chemists in the academia and industry who wish to keep abreast of rapid and important developments in the field.
Download or read book Tailored Metal Catalysts written by Y. Iwasawa and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 343 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Zeolite supported Noble Metal Clusters written by Fen Li and published by . This book was released on 2005 with total page 404 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book MgO supported Molecular Monometallic and Bimetallic Clusters written by Apoorva Kulkarni and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation is a report of the synthesis of family of osmium clusters and ruthenium-osmium clusters supported on MgO, their characterization by complementary spectroscopic and high-resolution microscopic methods, and an investigation of initial steps involved in the formation of the supported ruthenium-osmium clusters as well as their testing as catalysts for ethylene hydrogenation. Supported metal carbonyl clusters approximated as decaosmium carbonyls were prepared by reductive carbonylation of MgO-supported Os3(CO)12 at 548 K and 1 bar. The contrast in the atomic weights of the atoms makes the samples nearly optimum for characterization by scanning transmission electron microscopy (STEM), and the smallness and near uniformity of the clusters make the characterization by extended X-ray absorption fine structure (EXAFS) spectroscopy also nearly optimal. The rms (root-mean-square) radii of the undecarbonylated and partially decarbonylated clusters were found by HAADF-STEM to be 3.11 ± 0.09 and 3.06 ± 0.05 Å, respectively, and the close agreement between these values is consistent with the inference that the cluster frame was essentially the same in each. The average rms radius of the undecarbonylated clusters (2.94 ± 0.07 Å), agrees closely with rms radii determined from STEM. Supported triosmium clusters were synthesized from Os3(CO)12 on MgO powder. Conventional STEM images demonstrate a high degree of uniformity of the clusters, with average rms radii of 2.03 ± 0.06 Å. The EXAFS coordination number of 2.1 ± 0.4 confirms the presence of triosmium clusters on average and correspondingly determines an average rms cluster radius of 2.02 ± 0.04 Å. The high-resolution aberration-corrected STEM images show the individual Os atoms in the clusters, confirming the triangular structures of their frames and determining an Os-Os distance of 2.80 ± 0.14 Å, which matches the value of 2.89 ± 0.06 Å determined by EXAFS spectroscopy. The images also demonstrate the individual Os atoms in triosmium clusters atop Mg atoms on the MgO [110] surface, on the basis of which structural models were determined. Time-resolved EXAFS and IR spectra were recorded as the MgO-supported segregated triosmium and triruthenium clusters were treated in flowing hydrogen as the temperature was increased to 423 K. The data demonstrate, first, the decarbonylation of only triruthenium clusters starting at 333 K. The coordinatively unsaturated reactive ruthenium species at 333 K aggregated substantially so that the average ruthenium cluster was larger than triruthenium. When the temperature had been raised to about 358 K, the triosmium clusters underwent decarbonylation, and at approximately 398 K the triosmium clusters lost enough CO ligands to become sufficiently coordinatively unsaturated to allow reaction with Ru atoms. The family of supported bimetallic Ru-Os clusters was tested for ethylene hydrogenation catalysis. The results demonstrate the increase in activity with decarbonylation of supported clusters and increase in size of the Ru-Os clusters.
Download or read book Nanostructured Materials written by Jackie Ying and published by Academic Press. This book was released on 2001-12-14 with total page 244 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thematic volume of Advances in Chemical Engineering presents the latest advances in the exciting interdisciplinary field of nanostructured materials. Written by chemical engineers, chemists, physicists, materials scientists, and bioengineers, this volume focuses on the molecular engineering of materials at the nanometer scale for unique size-dependent properties. It describes a "bottom-up" approach to designing nanostructured systems for a variety of chemical, physical, and biological applications.
