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 858 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 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 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 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 Supported Platinum Rhodium and Iridium Clusters written by Zhengtian Xu and published by . This book was released on 1994 with total page 582 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Inclusion Chemistry with Zeolites Nanoscale Materials by Design written by Norman Herron and published by Springer Science & Business Media. This book was released on 1995 with total page 366 pages. Available in PDF, EPUB and Kindle. Book excerpt: Zeolites, with their crystalline microporous structure, are cordial hosts to a wide variety of guests. Traditional absorption techniques, as well as X-ray diffraction and spectroscopic techniques, have contributed to a better understanding of the nature of the host materials' characteristic cavities, cages and channels. The same techniques, coupled with powerful computational methods, have given new insights into the interactions of guest molecules with their hosts. In turn, this has led to new developments in the direction of structure during zeolite synthesis as well as potentially new applications of guest-host materials. The chapters in this text describe modern research in this field, detailing some of the studies on structure direction in synthesis, characterization techniques, computational aspects, co-ordination and organometallic chemistry, photochemistry, and electronic and optical materials.
Download or read book Pillared Clays and Related Catalysts written by Antonio Gil and published by Springer Science & Business Media. This book was released on 2010-08-28 with total page 531 pages. Available in PDF, EPUB and Kindle. Book excerpt: Since the first works introducing the aluminum intercalated clay family in the early 1970s, interest in the synthesis of pillared interlayered clays has increased tremendously, especially research into the properties and applications of new synthesis methods. The need for solids that could be used as cracking catalysts with larger pores than zeolitic materials has spurred the synthesis of new porous materials from clays. Pillared Clays and Related Catalysts reviews the properties and applications of pillared clays and other layered materials used as catalysts, focusing on: the acidity of pillared clays and the effect it has on catalytic performance the use of pillared clays as supports for catalytically active phases, and the use of the resulting solids in environmentally friendly reactions the applications of the selective reduction of NOx the comparison between the reactions of pillared clays and anionic clays.
Download or read book Rhodium Catalysis written by Carmen Claver and published by Springer. This book was released on 2017-12-15 with total page 291 pages. Available in PDF, EPUB and Kindle. Book excerpt: The series Topics in Organometallic Chemistry presents critical overviews of research results in organometallic chemistry. As our understanding of organometallic structure, properties and mechanisms increases, new ways are opened for the design of organometallic compounds and reactions tailored to the needs of such diverse areas as organic synthesis, medical research, biology and materials science. Thus the scope of coverage includes a broad range of topics of pure and applied organometallic chemistry, where new breakthroughs are being achieved that are of significance to a larger scientific audience. The individual volumes of Topics in Organometallic Chemistry are thematic. Review articles are generally invited by the volume editors. All chapters from Topics in Organometallic Chemistry are published OnlineFirst with an individual DOI. In references, Topics in Organometallic Chemistry is abbrev iated as Top Organomet Chem and cited as a journal.
Download or read book Catalyst Preparation written by John Regalbuto and published by CRC Press. This book was released on 2016-04-19 with total page 490 pages. Available in PDF, EPUB and Kindle. Book excerpt: This text explores the optimization of catalytic materials through traditional and novel methods of catalyst preparation, characterization, and monitoring for oxides, supported metals, zeolites, and heteropolyacids. It focuses on the synthesis of bulk materials and of heterogeneous materials, particularly at the nanoscale. The final chapters examine pretreatment, drying, finishing effects, and future applications involving catalyst preparation and the technological advances necessary for continued progress. Topics also include heat and mass transfer limitations, computation methods for predicting properties, and catalyst monitoring on laboratory and industrial scales.
Download or read book Supported Metal Complexes written by F.R. Hartley and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 331 pages. Available in PDF, EPUB and Kindle. Book excerpt: It is now IS years since the first patents in polymer supported metal complex catalysts were taken out. In the early days ion-exchange resins were used to support ionic metal complexes. Soon covalent links were developed, and after an initially slow start there was a period of explosive growth in the mid to late 1970s during which virtually every homogeneous metal complex catalyst ever reported was also studied bound to a support. Both polymers and inorganic oxides were studied as supports, although the great preponderance of workers studied polymeric supports, and of these polystyrene was by far the commonest used. This period served to show that by very careful design polymer-supported metal complex catalysts could have specific advantages over homogeneous metal complex catalysts. However the subject was a complicated one. Merely immobilising a successful metal complex catalyst to a functionalised support rarely yielded other than an inferior version of the catalyst. Amongst the many discouraging results of the 1970s, there were more than enough results that were sufficiently encouraging to demonstrate that, by careful design, supported metal complex catalysts could be prepared in which both the metal complex and the support combined together to produce an active catalyst which, due to the combination of support and complex, had advantages of activity, selectivity and specificity not found in homogeneous catalysts. Thus a new generation of catalysts was being developed.
Download or read book The Chemistry of the Catalyzed Hydrogenation of Carbon Monoxide written by G. Henrici-Olive and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 239 pages. Available in PDF, EPUB and Kindle. Book excerpt: During the oil embargo, in the winter 1973174, parts of Western Europe present ed an almost war-like aspect on Saturdays and Sundays: no traffic on the high ways, no crowds at ski resorts and other weekend entertainment places, no gaso line at the pumps. Living and teaching then in that part of the world, and discussing the situa tion with our students, we came to the conclusion that it would be timely to col lect the fine chemistry already known at the time in the field of conversion of coal to gasoline and other chemicals, and by this way help to draw the attention to this important alternative to crude oil. The idea of this book was born. The energy shock of the early seventies has been healthy and of great conse quences in chemistry. Large amounts of research money have been put to work since, and our knowledge of the possibilities and limitations of coal-based chemistry has increased enormously. During several years it appeared inap propriate to write a monograph about a topic which was in the midst of such an impetuous development. Nevertheless, we collected, and critically selected, the upcoming work as it appeared in the literature, and also tried to provide some modest input ourselves. Now, ten years later, the situation seems to be settled to a certain degree.
Download or read book Urea SCR Technology for deNOx After Treatment of Diesel Exhausts written by Isabella Nova and published by Springer Science & Business Media. This book was released on 2014-03-14 with total page 715 pages. Available in PDF, EPUB and Kindle. Book excerpt: Urea-SCR Technology for deNOx After Treatment of Diesel Exhausts presents a complete overview of the selective catalytic reduction of NOx by ammonia/urea. The book starts with an illustration of the technology in the framework of the current context (legislation, market, system configurations), covers the fundamental aspects of the SCR process (catalysts, chemistry, mechanism, kinetics) and analyzes its application to useful topics such as modeling of full scale monolith catalysts, control aspects, ammonia injections systems and integration with other devices for combined removal of pollutants.
Download or read book Catalytic Combustion written by Sophie A. Cottilard and published by . This book was released on 2011 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Catalytic combustion has been developed as a method of promoting efficient combustion over a wide range of air-to-fuel ratios with a minimum pollutant formation at low temperatures as compared to conventional flame combustion. In this book, the authors present current research in the study of catalytic combustion including commercial and industrial research in combustion and fluidisation engineering; the catalytic combustion of soot; using metal oxides to improve catalytic efficiency; catalytic combustion in the removal of pollutants from exhaust gases and in the energy conversion field and the catalytic combustion of methane using ceria-zirconia.
Download or read book Fundamentals of Chemical Reaction Engineering written by Mark E. Davis and published by Courier Corporation. This book was released on 2013-05-27 with total page 385 pages. Available in PDF, EPUB and Kindle. Book excerpt: Appropriate for a one-semester undergraduate or first-year graduate course, this text introduces the quantitative treatment of chemical reaction engineering. It covers both homogeneous and heterogeneous reacting systems and examines chemical reaction engineering as well as chemical reactor engineering. Each chapter contains numerous worked-out problems and real-world vignettes involving commercial applications, a feature widely praised by reviewers and teachers. 2003 edition.
Download or read book Natural Gas Conversion written by A. Holmen and published by Elsevier. This book was released on 1991-05-27 with total page 585 pages. Available in PDF, EPUB and Kindle. Book excerpt: These proceedings reflect the extensive fundamental and applied research efforts that are currently being made on the conversion of gas, in particular on the direct conversion of methane. The Symposium in Oslo focused on the following topics: Direct conversion of methane, Fischer-Tropsch chemistry, methanol conversion and natural gas conversion processes. The main aim was to present the state-of-the-art and progress currently being made within each of these areas. The book contains the papers presented and includes plenary lectures, short communications and posters. The papers will be of interest to scientists and engineers working in the field of gas conversion, transportation fuels, primary petrochemicals and catalysis.
Download or read book Catalyst Characterization written by Boris Imelik and published by Springer Science & Business Media. This book was released on 2013-06-29 with total page 720 pages. Available in PDF, EPUB and Kindle. Book excerpt: to the Fundamental and Applied Catalysis Series Catalysis is important academically and industrially. It plays an essential role in the manufacture of a wide range of products, from gasoline and plastics to fertilizers and herbicides, which would otherwise be unobtainable or prohibitive ly expensive. There are few chemical-or oil-based material items in modern society that do not depend in some way on a catalytic stage in their manufacture. Apart from manufacturing processes, catalysis is finding other important and over-increasing uses; for example, successful applications of catalysis in the control ofpollution and its use in environmental control are certain to in crease in the future. The commercial import an ce of catalysis and the diverse intellectual challenges of catalytic phenomena have stimulated study by a broad spectrum of scientists including chemists, physicists, chemical engineers, and material scientists. Increasing research activity over the years has brought deeper levels of understanding, and these have been associated with a continually growing amount of published material. As recentlyas sixty years ago, Rideal and Taylor could still treat the subject comprehensively in a single volume, but by the 19 50s Emmett required six volumes, and no conventional multivolume text could now cover the whole of catalysis in any depth.
