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 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 Models of Site isolated Cobalt Rhodium and Iridium Catalysts Supported on Zeolites written by and published by . This book was released on 2015 with total page 15 pages. Available in PDF, EPUB and Kindle. Book excerpt: The chemistry of zeolite-supported site-isolated cobalt, rhodium, and iridium complexes that are essentially molecular was investigated with density functional theory (DFT) and the results compared with experimentally determined spectra characterizing rhodium and iridium species formed by the reactions of Rh(C2H4)2(acac) and Ir(C2H4)2(acac) (acac = acetylacetonate) with acidic zeolites such as dealuminated HY zeolite. The experimental results characterize ligand exchange reactions and catalytic reactions of adsorbed ligands, including olefin hydrogenation and dimerization. Two molecular models were used to characterize various binding sites of the metal complexes in the zeolites, and the agreement between experimental and calculated infrared frequencies and metal-ligand distances determined by extended X-ray absorption fine structure spectroscopy was generally very good. The calculated structures and energies indicate a metal-support-oxygen (M(I)-O) coordination number of two for most of the supported complexes and a value of three when the ligands include the radicals C2H5 or H. The results characterizing various isomers of the supported metal complexes incorporating hydrocarbon ligands indicate that some carbene and carbyne ligands could form. Ligand bond dissociation energies (LDEs) are reported to explain the observed reactivity trends. The experimental observations of a stronger M-CO bond than M-(C2H4) bond for both Ir and Rh match the calculated LDEs, which show that the single-ligand LDEs of the mono and dual-ligand complexes for CO are similar to 12 and similar to 15 kcal/mol higher in energy (when the metal is Rh) and similar to 17 and similar to 20 kcal/mol higher (when the metal is Ir) than the single-ligand LDEs of the mono and dual ligand complexes for C2H4, respectively. The results provide a foundation for the prediction of the catalytic properties of numerous supported metal complexes, as summarized in detail here.

Download or read book Supported Mono and Bimetallic Complexes and Clusters written by Joseph David Kistler and published by . This book was released on 2014 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Site-isolated solid supported metal catalysts are important in industry and technology due to the cost efficiency to make and to recover and reuse them. These types of materials have catalytic properties similar to molecular complexes in solution while being easy to separate in heterogeneous catalytic reactions. The goal of this work was to synthesize supported metal complex catalysts while maintaining uniform catalytic sites. The syntheses were performed using precise glovebox and Schlenk techniques to achieve these highly uniform structures. These materials were then used to understand the relationship between structure of a catalytic site and the activity of the catalyst. This fundamental understanding of catalysts is important in advancing the field of catalysis. The structure of the catalysts were characterized using infrared (IR), extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) spectroscopies along with high angle annular dark field- scanning transmission electron microscopy (HAADF-STEM), with the HAADF-STEM work carried out by colleagues in other research groups. The catalytic activity of the catalysts was examined with gas chromatography (GC) and mass spectrometry (MS). The samples characterized in this work include complexes and clusters of second and third row transition metals supported on highly crystalline metal oxides. Specifically, there is a large focus in this work on supported rhodium complexes prepared from the organometallic precursor, Rh(C2H4)2(C5H7O2) and a pre-calcined magnesium oxide (MgO). This specific catalyst is important as not only is it active for olefin hydrogenation at mild temperatures but also there are reports of a unique surface mediated synthesis of uniform rhodium dimers, which are ideal for catalytic comparison of structures with different nuclearities. Reactivities of the MgO-supported rhodium complexes and dimers for carbon monoxide oxidation were investigated with the results showing the dimers were significantly more active for the reaction at 353 K. The stability of the dimers was tested in different reactive conditions with the results showing that under conditions with excess oxygen, the dimers are less stable and less active than under conditions with excess carbon monoxide.A bimetallic catalyst was synthesized on MgO incorporating rhodium and osmium using Rh(C2H4)2 (acac) and Os3(CO)12 as precursors. A unique synthesis method was developed to create a site-isolated segregated bimetallic catalyst with the osmium and rhodium sites acting independently of each other for ethylene hydrogenation at 298 K. The metals remained structurally segregated and catalytically independent even following reduction in H2 at 393 K. Zeolites, another class of highly crystalline supports, were studied to gain information on the support effects in catalysts. The analogous rhodium complexes as were synthesized on the MgO were synthesized on zeolite HY. These catalysts were tested to determine structural and catalytic stability under hydrogen, a reducing gas, and CO, a catalyst poison, with the results showing that, as compared to the complexes on zeolite HY, MgO-supported rhodium complexes form more uniform stable clusters under H2 and develop unique catalytic properties, selectivity for partial hydrogenation of dienes, when exposed to CO. Another zeolite, KLTL, was studied with supported platinum complexes synthesized from the salt precursor, Pt(NH3)4(NO3)2. This catalyst was oxidized at 633K to form supported single-atom platinum complexes. Both the as-prepared Pt(NH3)4 and oxidized PtOx complexes were analyzed structurally and studied as catalysts for CO oxidation. The oxidized platinum complexes proved to have significantly higher activity for CO oxidation at 423 K. Furthermore, HAADF-STEM was used to directly identify the locations of the platinum atoms in the pores of the zeolite before and after oxidative treatment, providing a method of ex-situ tracking of supported metal atoms.

Download or read book Synthesis Characterization and Catalytic Performance of Rhodium and Iridium Complexes Supported in Dealuminated HY Zeolite written by Claudia Martinez Macias and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Essentially molecular supported catalysts were synthesized by using organometallic complexes as precursors, such as Rh(CO)2(acac), Rh(C2H4)2(acac), Ir(CO)2(acac), and Ir(C2H4)2(acac) (where acac is acetylacetonate) and HY zeolite as a support. A goal was to obtain highly uniform solid catalysts with well-defined structures. Characterization by X-ray absorption (XAS) and infrared (IR) spectroscopies confirmed the anchoring of the metal to the support with a high degree of uniformity. IR and 29Si and 27Al nuclear magnetic resonance (NMR) spectra characterize the presence of amorphous regions in the zeolite, and scanning transmission electron microscopy (STEM) identifies these amorphous regions, where iridium is more susceptible to aggregation than in the crystalline regions. Treatment of Ir(CO)2/HY zeolite with C2H4 and H2 at room temperature led to a family of species which includes Ir(CO)2, Ir(CO)(C2H4), Ir(CO)(C2H4)2, Ir(CO)(C2H5) and, tentatively, Ir(CO)(H). The identification of the species is based on XAS and IR spectra (including spectra of samples made with isotopically labeled ligands, 13CO and D2O) and density functional theory (DFT) calculations. The catalytic performance of isostructural rhodium and iridium species incorporating CO as a ligand was measured for the ethylene conversion; the CO not only acts as an inhibitor but it also as a probe molecule providing information about the electronic properties of the metal and of the species present during reaction. When isostructural rhodium and iridium diethylene species are bonded near each other on HY zeolite, the iridium complexes alter the selectivity of rhodium by spilling over hydrogen that hinders the interaction between ethylene and the acidic sites of the zeolite that act in concert with the rhodium, causing it to favor ethylene hydrogenation over dimerization. All these results show how structurally simple solid catalysts can be used to facilitate fundamental understanding of catalysts and their performance.

Download or read book Rhodium Catalyzed Hydroformylation written by Piet W.N.M. van Leeuwen and published by Springer Science & Business Media. This book was released on 2006-04-11 with total page 291 pages. Available in PDF, EPUB and Kindle. Book excerpt: In the last decade there have been numerous advances in the area of rhodium-catalyzed hydroformylation, such as highly selective catalysts of industrial importance, new insights into mechanisms of the reaction, very selective asymmetric catalysts, in situ characterization and application to organic synthesis. The views on hydroformylation which still prevail in the current textbooks have become obsolete in several respects. Therefore, it was felt timely to collect these advances in a book. The book contains a series of chapters discussing several rhodium systems arranged according to ligand type, including asymmetric ligands, a chapter on applications in organic chemistry, a chapter on modern processes and separations, and a chapter on catalyst preparation and laboratory techniques. This book concentrates on highlights, rather than a concise review mentioning all articles in just one line. The book aims at an audience of advanced students, experts in the field, and scientists from related fields. The didactic approach also makes it useful as a guide for an advanced course.

Download or read book Surface and Nanomolecular Catalysis written by Ryan Richards and published by CRC Press. This book was released on 2006-05-25 with total page 555 pages. Available in PDF, EPUB and Kindle. Book excerpt: Using new instrumentation and experimental techniques that allow scientists to observe chemical reactions and molecular properties at the nanoscale, the authors of Surface and Nanomolecular Catalysis reveal new insights into the surface chemistry of catalysts and the reaction mechanisms that actually occur at a molecular level during catalys

Download or read book Modern Surface Organometallic Chemistry written by Jean-Marie Basset and published by John Wiley & Sons. This book was released on 2009-07-10 with total page 725 pages. Available in PDF, EPUB and Kindle. Book excerpt: Covering everything from the basics to recent applications, this monograph represents an advanced overview of the field. Edited by internationally acclaimed experts respected throughout the community, the book is clearly divided into sections on fundamental and applied surface organometallic chemistry. Backed by numerous examples from the recent literature, this is a key reference for all chemists.

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 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 2016-01-08 with total page 896 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 Microfluidics written by Yu Song and published by John Wiley & Sons. This book was released on 2018-05-07 with total page 576 pages. Available in PDF, EPUB and Kindle. Book excerpt: The first book offering a global overview of fundamental microfluidics and the wide range of possible applications, for example, in chemistry, biology, and biomedical science. As such, it summarizes recent progress in microfluidics, including its origin and development, the theoretical fundamentals, and fabrication techniques for microfluidic devices. The book also comprehensively covers the fluid mechanics, physics and chemistry as well as applications in such different fields as detection and synthesis of inorganic and organic materials. A useful reference for non-specialists and a basic guideline for research scientists and technicians already active in this field or intending to work in microfluidics.

Download or read book Rhodium Mediated Bond Activation written by and published by . This book was released on 2012 with total page 151 pages. Available in PDF, EPUB and Kindle. Book excerpt: Recently, our lab has developed monoanionic tridentate ligand, ToR, showing the corresponding coordination chemistry and catalyst reactivity of magnesium, zirconium, zinc and iridium complexes. This thesis details synthetic chemistry, structural study and catalytic reactivity of the ToR-supported rhodium compounds. Tl[ToR] has been proved to be a superior ligand transfer agent for synthesizing rhodium complexes. The salt metathesis route of Tl[ToM] with [Rh([mu]-Cl)(CO)]2 and [Rh([mu]- Cl)(COE)]2 gives ToMRh(CO)2 (2.2) and ToMRhH([beta]3-C8H13) (3.1) respectively while Tl[ToM] with [Rh([mu]-Cl)(CO)]2 affords ToPRh(CO)2 (2.3). 2.2 reacts with both strong and weak electrophiles, resulting in the oxazoline N-attacked and the metal center-attacked compounds correspondingly. Using one of the metal center-attacked electrophiles, 2.3 was demonstrated to give high diastereoselectivity. Parallel to COE allylic C-H activation complex 3.1, the propene and allylbenzene allylic C-H activation products have also been synthesized. The subsequent functionalization attempts have been examined by treating with Brønsted acids, Lewis acids, electrophiles, nucleophiles, 1,3-dipolar reagents and reagents containing multiple bonds able to be inserted. Various related complexes have been obtained under these conditions, in which one of the azide insertion compounds reductively eliminates to give an allylic functionalization product stoichiometrically. 3.1 reacts with various primary alcohols to give the decarbonylation dihydride complex ToMRh(H)2CO (4.1). 4.1 shows catalytic reactivity for primary alcohol decarbonylation under a photolytic condition. Meanwhile, 2.2 has been found to be more reactive than 4.1 for catalytic alcohol decarbonylation under the same condition. Various complexes and primary alcohols have been investigated as well. The proposed mechanism is based on the stochiometric reactions of the possible metal and organic intermediates. Primary amines, hypothesized to undergo a similar reaction pathway, have been verified to give dehydrogenative coupling product, imines. In the end, the well-developed neutral tridentate Tpm coordinates to the rhodium bis(ethylene) dimer in the presence of TlPF6 to give the cationic complex, [TpmRh(C2H4)2][PF6] (5.1). 5.1 serves as the first example of explicit determination of the solid state hapticity, evidenced by X-ray structure, among all the cationic TpmRM(C2H4)2+ (TpmR = Tpm, Tpm*, M = Rh, Ir) derivatives. The substitution chemistry of this compound has been studied by treating with soft and hard donors. The trimethylphosphine-sbustituted complex activates molecular hydrogen to give the dihydride compound.

Download or read book Synthetic and Spectroscopic Studies of Metal Carboxylate Dimers written by Joshua Telser and published by . This book was released on 2019-05-31 with total page 318 pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: Synthetic and spectroscopic studies on several complexes in the metal carboxylate series are described. These complexes are of general formula M 2 (02CR) 4 where M is a transition metal and "0 2 CR is a bridging carboxylate ligand. The metals used in this study are molybdenum, rhodium, and ruthenium. The studies were undertaken to help understand the nature of the metal -metal interaction in these complexes and to see what effect this interaction has on the reactivity of these complexes. To effect removal of the bridging carboxylate ligands, acetonitrile solutions of Rh2(0 2 CCH 2 CH 2 CH3) 4 and Mo 2 (0 2 CCH 3 ) 4 were reacted with stoichiometric amounts of the strong non-complexing acids CF3SO3H and (CH 3 CH 2 ) 20.HBF4 . This generated Rh2 (02 CH 2 CH 2 CH 3 ) 2 2+ and Mo 2 (02CCH 3 )? 2+ species in solution. The former was not isolated, but characterized in solution by NMR and UV-visible spectroscopy. Two derivatives of Mo 2 (02 CCH 3 ) 2 2+ were isolated: CMo 2 (0 2 CCH3) 2 (CH 3 CN) 4 ](CF 3 S03) 2 and [Mo 2 (0 2 CCH3) 2 (CH3CN) 5 ](BF 3 0H) 2 . The reactivity of the former complex towards oxidative addition was investigated. The complex was found to be quite stable towards oxidation in contrast to other Mo(II) complexes. Rhodium trifluoroacetate was reacted with various Lewis bases to give adducts of general formula Rh2 ( 02^3)482 as had been previously reported for Rh 2 (0 2 CR)4. However, with pyridine and £-butyl Isonitrile, complexes of general formula Rh2(0 2CCF3)4B4 were isolated constituting a new class of adduct. With phosphorus donors, Rh-Rh bond cleavage occurred to give monomeric Rh(I) and Rh(III) complexes. This demonstrates enhanced reactivity for Rh2(02CCF3)4 compared to rhodium alkyl carboxylate dimers. The chemical and electrochemical generation of Rh2(02CCH 2 CH 2CH3)4B2 + is described. These results and EPR spectra of these species are explained using a molecular orbital model. The strength of the rhodium Lewis base interaction determines the chemical and spectroscopic properties of these species. The formally mixed oxidation state complex Ru2(02CCH2CH2CH3)4Cl was studied by powder magnetic susceptibility measurements over the temperature range 5-300 K, by EPR spectroscopy In various glasses at 4 K and by Far IR spectroscopy at room temperature. In agreement with previous reports, the complex has a quartet ground state with unpaired electron spin density delocalized over both Ru atoms. Reactivity studies of this compound with Lewis bases are described. A bispyridine adduct of ruthenium butyrate chloride is reported. Dissertation Discovery Company and University of Florida are dedicated to making scholarly works more discoverable and accessible throughout the world. This dissertation, "Synthetic and Spectroscopic Studies of Metal Carboxylate Dimers" by Joshua A. Telser, was obtained from University of Florida and is being sold with permission from the author. A digital copy of this work may also be found in the university's institutional repository, IR@UF. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation.

Download or read book Supported Metal Complexes written by F.R. Hartley and published by Springer Science & Business Media. This book was released on 1985-11-30 with total page 346 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 Gold Nanoparticles written by Mohammed Muzibur Rahman and published by BoD – Books on Demand. This book was released on 2019-02-13 with total page 172 pages. Available in PDF, EPUB and Kindle. Book excerpt: Gold Nanoparticles - Reaching New Heights contains recent research on the preparation, characterization, fabrication, and potential of optical and biological applications of gold nanoparticles (AuNPs). It is promising novel research that has received a lot of interest over the last few decades. It covers advanced topics on optical, physical, medicinal, and biological applications of AuNPs. Development of green nanotechnology is generating the interest of researchers towards the synthesis of eco-friendly, safe, non-toxic applications, which can be used for manufacture at a large scale. These are simple, cost-effective, stable, enduring, and reproducible aqueous room temperature synthesis applications to obtain the self-assembly of AuNPs. This potentially unique work offers various approaches to R

Download or read book Atomically Precise Methods for Synthesis of Solid Catalysts written by Sophie Hermans and published by Royal Society of Chemistry. This book was released on 2015 with total page 318 pages. Available in PDF, EPUB and Kindle. Book excerpt: With techniques bridging the gap between surface science and heterogeneous catalysis the book presents a tool-kit for anyone wishing to prepare and define solid catalysts.