Showing papers on "Dehydrogenation published in 2007"
TL;DR: The scaling model is developed into a general framework for estimating the reaction energies for hydrogenation and dehydrogenation reactions and it is found that the adsorption energy of any of the molecules considered scales approximately with the adhesion energy of the central, C, N, O, or S atom.
Abstract: Density functional theory calculations are presented for CHx, x=0,1,2,3, NHx, x=0,1,2, OHx, x=0,1, and SHx, x=0,1 adsorption on a range of close-packed and stepped transition-metal surfaces. We find that the adsorption energy of any of the molecules considered scales approximately with the adsorption energy of the central, C, N, O, or S atom, the scaling constant depending only on x. A model is proposed to understand this behavior. The scaling model is developed into a general framework for estimating the reaction energies for hydrogenation and dehydrogenation reactions.
1,232 citations
TL;DR: In this article, a review examines the recent literature on the oxidative dehydrogenation (ODH) of ethane and propane, which aims for the synthesis of the corresponding alkenes.
871 citations
TL;DR: The first example of a homogeneous first row transition-metal-based catalyst which is active for dehydrogenation of ammonia−borane, H3NBH3, a promising chemical hydrogen storage material is reported, suggesting both N−H and B−H bonds are being broken in the rate-determining step(s).
Abstract: We report here the first example of a homogeneous first row transition-metal-based catalyst which is active for dehydrogenation of ammonia−borane, H3NBH3, a promising chemical hydrogen storage material. Addition of ammonia−borane to an active catalyst formed in situ from the reaction of Ni(cod)2 and 2 equiv of an appropriate N-heterocyclic carbene (NHC) rapidly evolves hydrogen at 60 °C. Using a gas burette to quantify the gas evolved, 29 of a possible 31 mL of H2 for 3 equiv of H2 was produced, equating to >2.5 equiv of H2 from ammonia−borane. Kinetic isotope effects of deuterated derivatives of ammonia−borane suggest that both N−H and B−H bonds are being broken in the rate-determining step(s).
608 citations
371 citations
TL;DR: In this paper, the authors describe approaches for modifying the thermodynamics and kinetics of hydrogen sorption reactions in light-metal hydrides using additives that form new compounds during dehydrogenation.
327 citations
TL;DR: Various secondary alcohols can be dehydrogenatively oxidized to ketones under neutral conditions with high turnover numbers by using the new Cp*Ir catalyst.
269 citations
TL;DR: For fine chemicals, high initial selectivities enable titania to address most of the twelve principles of "green chemistry", such as the synthesis of 4-tert-butyl-benzaldehyde, an important intermediate in perfume industry by direct selective oxidation of4-terT- butyl-toluene with air.
210 citations
187 citations
TL;DR: In this article, the thermodynamically and kinetically stable region of the H2 pressure−temperature phase diagram for reversible hydrogen storage in TiCl3-catalyzed LiBH4 + 1/2MgH2 was established.
Abstract: The coupled system LiBH4 + 1/2MgH2 ↔ LiH + 1/2MgB2 + 2H2 demonstrates improved hydrogen cycling thermodynamics compared to either LiBH4 or MgH2 alone; in effect, formation of MgB2 “destabilizes” the decomposition of LiBH4. Here we establish the thermodynamically and kinetically stable region of the H2 pressure−temperature phase diagram for reversible hydrogen storage in TiCl3-catalyzed LiBH4 + 1/2MgH2. Although MgB2 formation was thermodynamically favored at elevated temperature, it was kinetically more favorable for MgH2 and LiBH4 to decompose independently in a two-step dehydrogenation starting with MgH2 ↔ Mg + H2. At high temperature and low H2 pressure, direct LiBH4 decomposition is both thermodynamically allowed and kinetically favored; thus, the second dehydrogenation step from LiBH4 produced LiH and amorphous boron along with the Mg metal from the first step. From this state, recombination of LiH with amorphous boron had very poor kinetics and the system did not fully rehydrogenate. Applying an H2 ...
181 citations
TL;DR: In this article, the authors investigated possible mechanisms of oxidative dehydrogenation of propane using density functional theory and found that the rate of propene formation after readsorption on OVV sites is much large.
Abstract: We investigate possible mechanisms of oxidative dehydrogenation of propane using density functional theory. Monomeric vanadium oxide species supported on silica are modeled by vanadyl-substituted silsesquioxane. Similarly to other catalysts with transition metal oxo bonds, the initial C−H bond activation step is hydrogen abstraction by the vanadyl (OVV) group yielding a diradical intermediate in which a propyl radical is bound to a HO−VIV site. This is followed by a propyl rebound mechanism yielding alkoxide or alcohol attached to a VIII(OSi)3 surface site from which propene can be formed. Propene is also directly obtained by a second hydrogen abstraction from the diradical intermediate. Desorption of propyl radicals leads to a stationary concentration of propyl in the gas phase and leaves reduced HO−VIV sites on the surface. Due to fast reoxidation their concentration is much smaller than the concentration of OVV sites. Therefore the rate of propene formation after readsorption on OVV sites is much large...
171 citations
TL;DR: In this paper, the performance of ethanol reforming over nickel catalysts supported on lanthanum loaded Al 2 O 3 substrates was studied and the results revealed the enhancement in the reforming stability of the Ni catalysts with the increase in the lanthanums loading on Al 2 o 3 substrate.
TL;DR: Catalytic dehydrogenation of R(2)NHBH(3) (R = Me, H) promoted by a family of bis(cyclopentadienyl)titanium and bis(indenyl)zirconium compounds is reported; structure-reactivity relationships as a function of cyclopentadiensyl and indenyl substituents have been examined.
TL;DR: In this paper, the catalytic properties of sp 3 -hybridized ultra-dispersed diamond and sp 2 -sybridized onion-like carbon in the oxidative dehydrogenation of ethylbenzene to styrene were investigated, highlighting the structure sensitivity of the reaction.
TL;DR: In this article, experimental approaches for altering the thermodynamics and kinetics of light element hydride systems are discussed, and the catalytic effects of a variety of transition metal sources on hydrogen exchange in the LiBH 4 /MgH 2 system are described.
TL;DR: Defect-site enriched nanocrystalline ceria prepared by an alcoholysis method favors oxidative dehydrogenation of ethylbenzene using nitrous oxide with high conversion and selectivity at much lower temperatures compared to ceria samples prepared by other conventional methods.
Abstract: Defect-site enriched nanocrystalline ceria prepared by an alcoholysis method favors oxidative dehydrogenation of ethylbenzene using nitrous oxide with high conversion and selectivity at much lower temperatures compared to ceria samples prepared by other conventional methods. A direct correlation exists between the concentration of −Ce4+−O-−Ce3+-type defect sites and the reaction rates and, hence, the activation temperature required for the reaction.
TL;DR: In this article, the authors explored the mechanism by which ROH model reagents are activated on the surface of the Pt/partially reduced ceria catalyst using a combination of reaction testing and infrared spectroscopy.
TL;DR: Bulk gold powder (approximately 10(3) nm particle size) is a highly active catalyst for the oxidative dehydrogenation of secondary amines to imines under the mild conditions of 1 atm O2 and 60-100 degrees C.
TL;DR: In this paper, the effect of transition metal fluorides on the dehydrogenation and hydrogenation of MgH2 has been investigated and it is suggested that hydride phases formed by the reaction between Mg H2 and these transition metal FAs during milling and/or hydrogenation play a key role in improving the hydrogenation kinetics.
TL;DR: In this paper, the influence of zinc addition to alumina supported Pt and PtSn catalysts is analyzed not only on the activity, selectivity and deactivation in the propane dehydrogenation reaction, but also on the characteristics of platinum metal phase.
Abstract: The influence of the zinc addition to alumina supported Pt and PtSn catalysts is analyzed in this paper, not only on the activity, selectivity and deactivation in the propane dehydrogenation reaction, but also on the characteristics of platinum metal phase. Zinc can give a remarkable improvement in dehydrogenation performance of catalysts. High propylene selectivity (≥97%) can be obtained over zinc-doped catalysts. Physicochemical technologies like BET, NH 3 -TPD, H 2 -TPR, H 2 -chemisorption, C 3 H 6 -TPD, CO-FTIR and TPO were used to characterize the metal phase of catalysts. The presence of zinc modifies the metallic phase, mainly by geometric and electronic modifications of the metallic phase. These modifications could be responsible for the improvement of catalytic performance.
TL;DR: LiBH 4 nanoparticles supported by disordered mesoporous carbon CMK-3, denoted as nano- LiBH4 / C mesoporus, were synthesized in the present work.
TL;DR: The Mg2.9Ni film with preferential orientated nanocrystalline structure was obtained by magnetron sputtering and the hydrogen storage properties and microstructure were investigated by pressure-composition-isotherms measurement, x-ray diffraction and transmission electron microscopy as mentioned in this paper.
Abstract: The Mg2.9Ni film with preferential orientated nanocrystalline structure was obtained by magnetron sputtering. The hydrogen storage properties and microstructure were investigated by pressure-composition-isotherms measurement, x-ray diffraction and transmission electron microscopy. A reversible hydrogen storage content of about 4.45mass% at 497K has been obtained. The preferential orientation of the deposited film was destroyed after only one hydrogenation/dehydrogenation cycle. Both experiment and simplified calculation results proved that the hydrogenation/dehydrogenation reaction temperature decreases due to the extra interfacial free energy stored in the boundary, which demonstrate that Mg based hydride can be substantially destabilized by inducing nanocrystalline structure.
TL;DR: In this article, the anodic Pt-Ru-Ni/C and the Pt−Ru/C catalysts for potential application in direct methanol fuel cell (DMFC) were prepared by chemical reduction method.
TL;DR: In this paper, the hydrogen storage properties of LiBH4 ball milled with various ratios of carbon nanotubes (Cnano) were investigated, and the rehydrogenation results revealed that the Li2C2, formed during the dehydrogenation, could be reversed to LiH, in which the hydrogen capacity corresponds to 1∕4 of the original hydrogen content.
Abstract: The hydrogen storage properties of LiBH4 ball milled with various ratios of carbon nanotubes (Cnano) were investigated. The LiBH4∕Cnano mixtures showed superior dehydrogenation, hydrogen desorption starting at 250°C, and the majority of hydrogen being released below 600°C. The rehydrogenation results revealed that the Li2C2, formed during the dehydrogenation, could be reversed to LiH, in which the hydrogen capacity corresponds to 1∕4 of the original hydrogen content of LiBH4, and C at 10MPa hydrogen pressure and 400°C.
TL;DR: In this article, the adsorption and decomposition of ammonia on the (111) and (100) surfaces of platinum-group metals (Pd, Rh, Pt).
Abstract: Periodic DFT calculations using plane waves have been applied to comparatively study the adsorption and decomposition of ammonia on the (111) and (100) surfaces of platinum-group metals (Pd, Rh, Pt). Different adsorption geometries and positions have been studied for NH3 and its dehydrogenation intermediates (NHx, x = 0, 1, 2). On the six surfaces investigated, NH3 adsorbs preferentially on top sites, NH2 on bridge, and NH and N on hollow sites. However, the adsorption energies of the NHx moieties differ considerably from one surface to another. All of the species adsorb more strongly on the (100) than on the (111) planes. Rh(100) provides the maximum stability for the various intermediates. The reaction energies, the structure of the transition states, and the activation barriers of the successive dehydrogenation steps (NHx → NHx-1 + H) have been determined, making it possible to compute rate coefficients at different temperatures. Our calculations have confirmed that ammonia decomposition over noble met...
01 Jan 2007
TL;DR: Sunley as mentioned in this paper discusses the role of the catalyst in the formation of C-O bonds by Oxidation and discusses the relationship between the catalyst and the substrate of a metal. But this paper is not a comprehensive review of the chemical process.
Abstract: Preface Glossary Chapter 1: Introduction - Catalysis in the Chemical Industry Sunley 1.1: Catalysis in the Chemical Industry 1.2: Selection of a Chemical Process: What Does the Catalyst Do? 1.3: Developing Metal-Catalysis - the Role of Fundamental Understanding References Chapter 2: Formation of C-O Bonds by Oxidation 2.1: Review - The Basic Chemistry of Oxygen 2.2: Cyclohexane Oxidation to Cyclohexanol and Cyclohexanone and to Adipic Acid: on the Way to Nylon-6,6 2.3: p-Xylene Oxidation to Terephthalic Acid. Polyethylene Terephthalate: on the Way to Fibres for Shirts 2.4: Ethylene Oxide by Ag-catalyzed Oxidation of Ethylene: for Antifreeze and Detergents 2.5: Propylene Oxide: to Biocompatible Propylene Glycol 2.6: Hydrogen Peroxide Route to Propylene Oxide 2.7: Asymmetric Epoxidation, Dihydroxylation and Sulfide Oxidation: New Routes to Chiral Agrochemicals and Pharmaceuticals 2.8: Acrolein and Acrylic Acid from Propylene: for Super-Absorbent Polymers, Paints, and Fibres 2.9: Methacrolein and Methacrylic Acid from Isobutene 2.10: Ammoxidation Reactions. Propylene to Acrylonitrile: for Engineering Plastics, Polymers 2.11: Maleic Anhydride and Phthalic Anhydride: for THF, Spandex, Swim-suits and Ladies' Tights 2.12: Silicalite Process to e-Caprolactam 2.13: Oxidation of Phenol to Catechol and Hydroquinone 2.14: Benzene Oxidation to Phenol: Making Phenolic Resins for Building 2.15: Oxidation Processes in which the Metal Directly Functionalizes the Olefinic Substrate 2.16: Enzymatic and Microbiological Oxidations. Microbial Hydroxylation of Progesterone Annex 1: Alkane Feedstocks. Alternative Routes to Acetic Acid and Acrylonitrile Annex 2: Adsorption Effects on the Catalytic Performances of TS-1. Zeolites as Solid Solvents References Chapter 3: Hydrogenation Reactions 3.1: Introduction and Basic Chemistry: Activation of Hydrogen and Transfer to Substrate Isomerization Reactions 3.2: Hydrotreating in Petroleum Chemistry 3.3: Mono-unsaturated Fatty Esters by Partial Hydrogenation of Natural Oils 3.4: Hydrogenation of Adiponitrile to Hexamethylenediamine 3.5: Making L-DOPA by Enantioselective Hydrogenation of Acetamidoarylacrylic Acids 3.6: Enantioselective Hydrogenation of N-Arylimines in the Synthesis of the Chiral Herbicide, (S )-Metolachlor 3.7: Isomerization Reactions: Diethylgeranylamine and Diethylnerylamine for the Production of (_)-Menthol 3.8: Enantioselective Hydrogen Transfer 3.9: Ethylbenzene Dehydrogenation to Styrene Discussion Points References Chapter 4: Syntheses Based on Carbon Monoxide 4.1: Introduction 4.2: Carbonylation Reactions of Alcohols and Esters 4.3: Hydroxy/Alkoxy-Carbonylation of Alkenes and Dienes 4.4: Polyketones 4.5: Oxidative Carbonylation of Methanol to Dimethyl Carbonate and Dimethyl Oxalate 4.6: Hydroformylation of Olefins 4.7: CO Hydrogenation Annex 1: Concerning the Mechanism of the Fischer-Tropsch Reaction Annex 2: Some Hints for Discussion Points References Chapter 5: Carbon-Carbon Bond Formation 5.1: Introduction 5.2: Alkylation and Related Reactions 5.3: Carbon-Carbon Bond Formation through Activation of Aryl- or Vinyl-Halide bonds: Fine Chemicals 5.4: Chemistry of Allyl Compounds. Butadiene as Substrate 5.5: Oligomerization of Olefins 5.6: Carbene Chemistry and Asymmetric Synthesis: Chrysanthemic Esters Annex 1: Devising New Synthetic Pathways Annex 2: Hints to Improve or to Develop Alternative Processes for the Synthesis of Aromatics Catalyzed by Transition Metals Annex 3: Perspectives in C-C Bond Forming Organic Syntheses References Chapter 6: Metathesis of Olefins 6.1: Introduction - History and Basic Chemistry of Metathesis 6.2: The Carbene-Metallacyclobutane Mechanism of Metathesis 6.3: Industrial Applications of Metathesis 6.4: Homogeneous Ruthenium Alkylidene Complexes 6.5: Speciality Polymers 6.6: Fine Chemicals and Pharmaceuticals 6.7: Recent Progress 6.8: Future Outlook References Chapter 7: Polymerization Reactions 7.1: An Introductory Overview 7.2: Industrial Aspects of Polyolefin Production 7.3: Solid-State Polymerization Catalysts 7.4: Soluble Olefin Polymerization Catalysts 7.5: Supported Metallocene Catalysts 7.6: Copolymerization of Linear and Cyclic Olefins 7.7: Copolymerisation of Olefins with Polar Monomers and with CO Annex 1: Polymer Stereochemistry Studied by 13C NMR Spectroscopy Annex 2: Stereospecific Polymerization of Conjugated Diolefins: Butadiene and Isoprene Annex 3: Some Hints to Help Start the Discussions Acknowledgements References Appendix 1: Basic Organometallic Chemistry Related to Catalytic Cycles References Appendix 2: Some Basic Aspects of Surface Science Related to Heterogeneously Catalyzed Reactions References Subject Index
TL;DR: In this article, structural characterization and oxidative dehydrogenation activity of CeO2/Al2O3 and V2O5/CeO 2/Al 2O3 catalysts for Ebenzene to styrene were investigated systematically.
Abstract: Structural characterization and oxidative dehydrogenation activity of CeO2/Al2O3 and V2O5/CeO2/Al2O3 catalysts for ethylbenzene (EB) to styrene were investigated systematically. The CeO2/Al2O3 catalyst was prepared by a deposition precipitation method, and a theoretical monolayer equivalent of 10 wt % V2O5 was dispersed over its surface by a wet impregnation method to obtain the V2O5/CeO2/Al2O3 catalyst. To understand thermal and textural stability, the synthesized catalysts were subjected to calcination at various temperatures (773−1073 K). Physicochemical characterization was performed using X-ray diffraction (XRD), Raman spectroscopy (RS), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis, and BET surface area techniques. The XRD and RS results suggested that the CeO2/Al2O3 sample is thermally quite stable up to 1073 K and that the ceria exists in the form of an over layer on the surface of the alumina support. In the case of the V2O5/CeO2/Al2O3 sample, no crystalline V2O5 was observed...
TL;DR: In this article, the titanocene-catalyzed dehydrocoupling of the adduct Me2NH·BH3 has been investigated by density functional theory (B3LYP).
TL;DR: In this article, an iridium-nitrogen-radical complex is shown to be a highly active and selective catalyst for the dehydrogenation (oxidation) of primary alcohols to aldehydes in the presence of the oxidant benzoquinone.
Abstract: (Chemical Equation Presented) A little goes a long way: An iridium-nitrogen-radical complex is a highly active and selective catalyst for the dehydrogenation (oxidation) of primary alcohols to aldehydes in the presence of the oxidant benzoquinone (see simplified scheme). With only 0.01 mol% of the complex, turnover frequencies of up to 150 000 s-1 are reached.
TL;DR: In this paper, a catalytic dehydrogenation of alkyl amines with a Co(I) catalyst has been proposed to yield a broad range of stable protected enamines and 1,2-diheteroatom-substituted alkenes.
Abstract: C-H bond activation has been extensively studied with (Cp*)M(L)n (M = Ir, Rh), but cobalt, the third member of this triad, has not previously been shown to activate sp3 C-H bonds. Further, practical functionalization of the metal alkyl products of oxidative addition has not been fully explored. Toward these ends, we have developed catalytic dehydrogenation of alkyl amines with a Co(I) catalyst. Amine substrates are protected with vinyl silanes, followed by catalytic transfer hydrogenation, to yield a broad range of stable protected enamines and 1,2-diheteroatom-substituted alkenes, including several unprecedented heterocycles. (Cp*)Co(VTMS)2 catalyzes transfer hydrogenation under surprisingly mild conditions with high chemo-, regio-, and diastereoselectivity, while tolerating additional functionality.
TL;DR: PtSnNaLa/ZSM-5 catalysts with different amounts of lanthanum were prepared by sequential impregnation method, and characterized by XRD, nitrogen adsorption, NH 3 -TPD, FT-IR, TPR, H 2 -tPD, XPS and TPO techniques as mentioned in this paper.
Abstract: PtSnNaLa/ZSM-5 catalysts with different amounts of lanthanum were prepared by sequential impregnation method, and characterized by XRD, nitrogen adsorption, NH 3 -TPD, FT-IR, TPR, H 2 -TPD, XPS and TPO techniques. It was found that the La species were well dispersed on the internal and external surfaces of ZSM-5 zeolite. With a little addition of La, the catalyst acidity decreased slightly and the active sites of the catalyst were stabilized, which resulted in the increased catalytic selectivity and stability. In PtSnNaLa/ZSM-5 catalyst containing 1.4% La, the stability of catalyst reached the best state and the catalytic selectivity was at the maximum. The average yield of propene was about 35.2% over 80 h for the reaction of propane dehydrogenation at 590 °C. However, as the La content increased, the character of Pt active sites changed obviously and the amount of Lewis acid sites increased, which in consequence decreased the catalytic activity and selectivity. Results from XPS analysis indicated that the addition of La could inhibit the reduction of tin species. Temperature-programmed oxidation (TPO) experiments showed that suitable loading of La could prevent the catalyst from coking effectively, whereas the opposite effect was observed when the content of La was excess.