Showing papers on "Dehydrogenation published in 2010"
1,325 citations
TL;DR: The as-synthesized Ni nanoparticles supported on the Ketjen carbon support exhibit high catalytic activity in hydrogen generation from the hydrolysis of the ammonia-borane (H( 3)NBH(3)) complex with a total turnover frequency value of 8.8 mol.
Abstract: Monodisperse nickel nanoparticles are prepared from the reduction of Ni(acac)2 with borane tributylamine in the presence of oleylamine and oleic acid. Without any special treatment to remove the surfactants, the as-synthesized Ni nanoparticles supported on the Ketjen carbon support exhibit high catalytic activity in hydrogen generation from the hydrolysis of the ammonia−borane (H3NBH3) complex with a total turnover frequency value of 8.8 mol of H2·(mol of Ni)−1·min−1. Such catalysis based on Ni nanoparticles represents a promising step toward the practical development of the H3NBH3 complex as a feasible hydrogen storage medium for fuel cell applications.
458 citations
TL;DR: Magnetically recyclable Au@Co core-shell nanoparticles were successfully synthesized in a one-step seeding-growth process and exhibited higher catalytic activity toward the dehydrogenation of ammonia borane than Au-Co alloy and the pure metal counterparts.
Abstract: Magnetically recyclable Au@Co core−shell nanoparticles were successfully synthesized in a one-step seeding-growth process within a few minutes. They were thermally stable and exhibited higher catalytic activity toward the dehydrogenation of ammonia borane than Au−Co alloy and the pure metal counterparts. This is a large enhancement in the catalytic activity of core−shell structured nanoparticles and will provide a new design principle for heterogeneous catalysis.
445 citations
TL;DR: In this article, the deactivation of catalysts during methanol conversion is investigated for elucidating how spatial constraints interfere mechanistically, and detailed product composition, including retained organic matter, is determined in a time resolved mode.
313 citations
TL;DR: In this article, the authors explored the kinetically coupled reactions of glycerol in water over bifunctional Pt/Al2O3 catalysts and found that larger Pt particles favor hydrodeoxygenation over complete deconstruction to hydrogen and CO2.
264 citations
TL;DR: The ability to use a variety of catalysts to prepare polyaminoboranes suggests that the synthetic strategy should be applicable to a broad range of amine-borane precursors and is a promising development for this new class of inorganic polymers.
Abstract: The catalytic dehydrocoupling/dehydrogenation of N-methylamine-borane, MeNH2·BH3 (7), to yield the soluble, high molecular weight poly(N-methylaminoborane) (8a), [MeNH−BH2]n (MW > 20 000), has been achieved at 20 °C using Brookhart’s Ir(III) pincer complex IrH2POCOP (5) (POCOP = [μ3-1,3-(OPtBu2)2C6H3]) as a catalyst. The analogous reaction with ammonia-borane, NH3·BH3 (4), gave an insoluble product, [NH2−BH2]n (8d), but copolymerization with MeNH2·BH3 gave soluble random copolymers, [MeNH−BH2]n-r-[NH2−BH2]m (8b and 8c). The structures of polyaminoborane 8a and copolymers 8b and 8c were further analyzed by ultrahigh resolution electrospray mass spectrometry (ESI-MS), and 8a, together with insoluble homopolymer 8d, was also characterized by 11B and 1H solid-state NMR, IR, and wide-angle X-ray scattering (WAXS). The data indicate that 8a−8c are essentially linear, high molecular weight materials and that the insoluble polyaminoborane 8d possesses a similar structure but is of lower molecular weight (ca. 20 r...
262 citations
TL;DR: In this article, the catalytic performances of Pt/Al2O3 and Pt-Sn/Al 2O3 catalysts for the dehydrogenation of propane through consecutive reaction-regeneration cycles have been studied under realistic reaction conditions.
243 citations
TL;DR: The fate of amine-boranes upon coordination to a metal center is discussed with a particular emphasis on B-H activation pathways, which includes the coordination of aminoborane, the simplest unit resulting from dihydrogen release of ammonia-borane.
Abstract: There have been a number of approaches developed for the catalyzed dehydrogenation of amine-boranes as potential dihydrogen sources for hydrogen storage applications in recent years. Key advances in this area have been recently made thanks to catalytic and stoichiometric studies. In this Minireview, the fate of amine-boranes upon coordination to a metal center is discussed with a particular emphasis on B-H activation pathways. We focus on the few cases in which coordination of the resulting dehydrogenated product could be achieved, which includes the coordination of aminoborane, the simplest unit resulting from dihydrogen release of ammonia-borane.
222 citations
TL;DR: The results point to the active role of PPh(3) ligands, which undergo significant conformational changes as the reaction occurs, and provide insights into the role of the base, which acts as a "co-catalyst" by facilitating proton transfers within active species.
Abstract: We report a comprehensive density functional theory (DFT) study of the mechanism of the methanol dehydrogenation reaction catalyzed by [RuH2(H2)(PPh3)3] Using the B97-D dispersion-corrected functional, four pathways have been fully characterized, which differ in the way the critical β-hydrogen transfer step is brought about (eg, by prior dissociation of one PPh3 ligand) All these pathways are found to be competitive (ΔG⧧ = 270−321 kcal/mol at 150 °C) and strongly interlocked The reaction can thus follow multiple reaction channels, a feature which is expected to be at the origin of the good kinetics of this system Our results also point to the active role of PPh3 ligands, which undergo significant conformational changes as the reaction occurs, and provide insights into the role of the base, which acts as a “co-catalyst” by facilitating proton transfers within active species Activation barriers decrease on going from methanol to ethanol and 2-propanol substrates, in accord with experiment
209 citations
TL;DR: In this paper, the effects of Sn on the local environment of the dispersed Pt, the catalyst activity and selectivity for dehydrogenation, and the formation of coke were investigated.
200 citations
TL;DR: Amorphous and well dispersed Co nanoparticles (less than 10nm) have been in situ synthesized in aqueous solution at room temperature as discussed by the authors, which represents a promising step toward the development of ammonia borane as a viable on-board hydrogen storage and supply material.
TL;DR: The effect of the suppport on oxidative dehydrogenation activity for vanadia/ceria systems is examined for the oxidation of methanol to formaldehyde by use of well-defined VO(x)/CeO(2)(111) model catalysts.
Abstract: The effect of the suppport on oxidative dehydrogenation activity for vanadia/ceria systems is examined for the oxidation of methanol to formaldehyde by use of well-defined VO(x)/CeO(2)(111) model catalysts. Temperature-programmed desorption at low vanadia loadings revealed reactivity at much lower temperature (370 K) as compared to pure ceria and vanadia on inert supports such as silica. Density functional theory is applied and the energies of hydrogenation and oxygen vacancy formation also predict an enhanced reactivity of the vanadia/ceria system. At the origin of this support effect is the ability of ceria to stabilize reduced states by accommodating electrons in localized f-states.
TL;DR: The efficient catalytic dehydrocoupling of a range of amine-borane adducts by a series of group 4 metallocene type precatalysts has been demonstrated and the proposal of a two cycle, four step reaction mechanism is proposed.
Abstract: The efficient catalytic dehydrocoupling of a range of amine−borane adducts, R′RNH·BH3 (R′ = R = Me 1a; R′ = R = iPr 1b; R′ = Me, R = CH2Ph 1c) by a series of group 4 metallocene type precatalysts has been demonstrated. A reduction in catalytic activity was detected upon descending the group and also on substitution of the cyclopentadienyl (Cp) ligands with sterically bulky or electron-donating substituents. Precatalysts Cp2TiCl2/2nBuLi and Cp2Ti(PMe3)2, which are believed to act as precursors to [Cp2Ti], were found to promote the transformation of 1a to [Me2N-BH2]2 (3a) in a homogeneous catalytic process. Mechanistic studies identified the linear dimer Me2NH-BH2−NMe2-BH3 (2a) as a reaction intermediate, which subsequently undergoes further catalytic dehydrogenation to form cyclic dimer 3a. Synthesis of the 2H-isotopologues of 1a allowed the extraction of phenomenological kinetic isotope effects for 1a → 2a and 2a → 3a from initial rate data, which permitted the proposal of a catalytic cycle with plausible...
TL;DR: The as-synthesized Au-Ni@SiO(2) catalyst shows higher catalytic activity and better durability in the hydrolysis of ammonia borane, generating a nearly stoichiometric amount of hydrogen.
Abstract: Gold-nickel nanoparticles (NPs) of 3-4 nm diameter embedded in silica nanospheres of around 15 nm have been prepared by using [Au(en)(2)Cl(3)] and [Ni(NH(3))(6)Cl(2)] as precursors in a NP-5/cyclohexane reversed-micelle system, and by in situ reduction in an aqueous solution of NaBH(4)/NH(3)BH(3). Compared with monometallic Au@SiO(2) and Ni@SiO(2), the as-synthesized Au-Ni@SiO(2) catalyst shows higher catalytic activity and better durability in the hydrolysis of ammonia borane, generating a nearly stoichiometric amount of hydrogen. During the generation of H(2), the synergy effect between gold and nickel is apparent: The nickel species stabilizes the gold NPs and the existence of gold helps to improve the catalytic activity and durability of the nickel NPs.
TL;DR: MgH(2) nanoparticles with a size of <3 nm were formed by direct hydrogenation of Bu( 2)Mg inside the pores of a carbon scaffold by reducing activation energy and reaction enthalpy for the nanoconfined system.
TL;DR: In this paper, the authors investigated the performance of a Pt catalyst supported on a novel Mg(Ga)(Al)O mixed oxide support for the dehydrogenation of both ethane and propane.
TL;DR: Cationic Pd(II) complexes catalyzed the dehydrogenation of ammonia borane in the most efficient manner with the release of 2.0 equiv of H(2) in less than 60 s at 25 degrees C.
Abstract: Cationic Pd(II) complexes catalyzed the dehydrogenation of ammonia borane in the most efficient manner with the release of 2.0 equiv of H_2 in less than 60 s at 25 °C. Most of the hydrogen atoms were obtained from the boron atom of the ammonia borane. The first step of the dehydrogenation reaction was elaborated using density functional theory calculations.
TL;DR: The direct synthesis of amides from alcohols and amines is described with the simultaneous liberation of dihydrogen and shows any significant differences in reactivity, which indicates that the same catalytically active species is operating.
Abstract: The direct synthesis of amides from alcohols and amines is described with the simultaneous liberation of dihydrogen. The reaction does not require any stoichiometric additives or hydrogen acceptors and is catalyzed by ruthenium N-heterocyclic carbene complexes. Three different catalyst systems are presented that all employ 1,3-diisopropylimidazol-2-ylidene (IiPr) as the carbene ligand. In addition, potassium tert-butoxide and a tricycloalkylphosphine are required for the amidation to proceed. In the first system, the active catalyst is generated in situ from [RuCl 2 (cod)] (cod= 1,5-cyclooctadiene), 1,3-diisopropylimidazolium chloride, tricyclopentylphosphonium tetrafluoroborate, and base. The second system uses the complex [RuCl 2 (IiPr)(p-cymene)] together with tricyclohexylphosphine and base, whereas the third system employs the Hoveyda-Grubbs 1st-generation metathesis catalyst together with 1,3-diisopropylimidazolium chloride and base. A range of different primary alcohols and amines have been coupled in the presence of the three catalyst systems to afford the corresponding amides in moderate to excellent yields. The best results are obtained with sterically unhindered alcohols and amines. The three catalyst systems do not show any significant differences in reactivity, which indicates that the same catalytically active species is operating. The reaction is believed to proceed by initial dehydrogenation of the primary alcohol to the aldehyde that stays coordinated to ruthenium and is not released into the reaction mixture. Addition of the amine forms the hemiaminal that undergoes dehydrogenation to the amide. A catalytic cycle is proposed with the {(IiPr)Ru II } species as the catalytically active components.
TL;DR: Considering AB as a significantly polarized molecule, it is reasoned that it could be dehydrogenated by direct reaction with a similarly polarized unsaturated compound by the rarely explored reaction mode of double H transfer.
Abstract: Ammonia–borane (H3N-BH3, AB) is considered a feasible material for chemical hydrogen storage owing to its ideally very high storage capacity (19.6 weight% H) and thus has attracted much attention. Dehydrogenations of AB were accomplished either thermally or by transition metal catalysis. Considering AB as a significantly polarized molecule, we reasoned that it could be dehydrogenated by direct reaction with a similarly polarized unsaturated compound by the rarely explored reaction mode of double H transfer (Scheme 1).
TL;DR: In this paper, the effect of the dopant valence on the properties and catalytic behavior of Ni-based mixed metal oxides in the ethane oxidative dehydrogenation reaction was examined.
TL;DR: In this paper, a comparative mechanistic study of the MSR reaction on two key model systems, Cu(111) and Pd(111), with distinct selectivity using density functional theory calculations is presented.
Abstract: Methanol steam reforming (MSR) is an important industrial process for hydrogen production, and fundamental understanding of the reaction mechanism is crucial to improve the catalytic activity and selectivity. In the present work, we present a comparative mechanistic study of the MSR reaction on two key model systems, Cu(111) and Pd(111), with distinct selectivity using density functional theory calculations. We find that, on Cu(111), methanol dehydrogenation to formaldehyde is favorable first through the O−H bond scission, and the final products are dominated by carbon dioxide and hydrogen. On Pd(111), formaldehyde is also found to be an important intermediate; however, it comes through the C−H bond breaking first, and the final products are mainly CO and hydrogen. We find that the distinct selectivity on the Cu(111) and Pd(111) surfaces originates from the different reactivities of HCHO on the two surfaces. On Cu(111), HCHO tends to react with the hydroxyl to form hydroxymethoxy followed by its decomposi...
TL;DR: In this article, a review highlights the different direct stoichiometric and catalytic palladium procedures leading to α,β-unsaturated carbonyl compounds from the corresponding ketones, aldehydes, esters, lactones and amides.
TL;DR: Li et al. as discussed by the authors investigated the hydrogen storage properties of LiBH4 ball milled with TiF3, and they found that the mixture exhibited significantly improved dehydrogenation properties.
Abstract: The hydrogen storage properties of LiBH4 ball milled with TiF3 were investigated. It was found that the LiBH4–TiF3 mixture exhibited significantly improved dehydrogenation properties. For example, the LiBH4–TiF3 (mole ratio: 3 : 1) sample started to release hydrogen at around 100 °C, and the hydrogen desorption capacity reached 5.0 wt% at 250 °C. Furthermore, the dehydrogenated product can be partially rehydrogenated at 100 atm H2 and 350 °C. X-Ray diffraction (XRD), infrared (IR) spectroscopy and X-ray photoelectron spectroscopy (XPS) characterizations revealed that the decreased dehydrogenation conditions in the LiBH4–TiF3 system resulted from an exothermic reaction of 3LiBH4 + TiF3 → 3LiF + TiB2 + B + 6H2, which improved both its thermodynamics and kinetics. As the above reaction is exothermic, the reverse reaction is not feasible, further investigations indicated that the rehydrogenation may be due to the formation of another borohydride.
TL;DR: In this paper, the authors investigated the confinement of LiBH4 in ordered mesoporous SiO2 and its effect on the hydrogen sorption properties, and demonstrated that only under hydrogen pressure, melt infiltration is an effective method for the synthesis of Li BH4/SBA-15 nanocomposites.
Abstract: Lithium borohydride (LiBH4) is a promising material for hydrogen storage, with a gravimetric hydrogen content of 18.5%. However, the thermodynamics and kinetics of its hydrogen release and uptake need to be improved before it can meet the requirements for mobile applications. In this study, we investigate the confinement of LiBH4 in ordered mesoporous SiO2 and its effect on the hydrogen sorption properties. We demonstrate that, only under hydrogen pressure, melt infiltration is an effective method for the synthesis of LiBH4/SBA-15 nanocomposites. Our work clearly shows that formation of lithium silicates from LiBH4 and SiO2 can effectively be suppressed by hydrogen. Thus, under hydrogen pressure, LiBH4 can fully fill the mesopores of SBA-15 while the long-range order of the mesopores is maintained. The confined LiBH4 has enhanced hydrogen desorption properties, with desorption starting at 150 °C. However, upon dehydrogenation, SiO2 and decomposition products of LiBH4 react to form Li2SiO3 and Li4SiO4, lea...
TL;DR: In this article, the authors used density functional theory (DFT) calculations to study the hydrogenation of CHx and C2Hx sparsified polycyclic acid (C2HX) sparsification.
Abstract: Hydrogenation of ethylene and dehydrogenation and hydrogenolysis of ethane on Pt(111) and Pt(211) have been studied using density functional theory (DFT) calculations. Adsorption of CHx and C2Hx sp...
TL;DR: Hydrotalcite-supported gold nanoparticles with sizes of less than 5 nm are highly efficient and reusable catalysts for the oxidant-free dehydrogenation of alcohols to carbonyl compounds and hydrogen.
TL;DR: The DFT results predict that intermediate species like CH(3) and CH(2) are specially stabilized at sites located at particles edges and corners by an amount of 50-80 kJ mol(-1), which underlines the critical role of particle edge sites in methane activation and dehydrogenation.
Abstract: Complete dehydrogenation of methane is studied on model Pt catalysts by means of state-of-the-art DFT methods and by a combination of supersonic molecular beams with high-resolution photoelectron spectroscopy. The DFT results predict that intermediate species like CH 3 and CH 2 are specially stabilized at sites located at particles edges and corners by an amount of 50-80 kJ mol -1 . This stabilization is caused by an enhanced activity of low-coordinated sites accompanied by their special flexibility to accommodate adsorbates. The kinetics of the complete dehydrogenation of methane is substantially modified according to the reaction energy profiles when switching from Pt(111) extended surfaces to Pt nanoparticles. The CH 3 and CH 2 formation steps are endothermic on Pt-(111) but markedly exothermic on Pt 79 . An important decrease of the reaction barriers is observed in the latter case with values of approximately 60 kJ mol -1 for first C-H bond scission and 40 kJ mol -1 for methyl decomposition. DFT predictions are experimentally confirmed by methane decomposition on Pt nanoparticles supported on an ordered CeO 2 film on Cu(111). It is shown that CH 3 generated on the Pt nanoparticles undergoes spontaneous dehydrogenation at 100 K. This is in sharp contrast to previous results on Pt single-crystal surfaces in which CH 3 was stable up to much higher temperatures. This result underlines the critical role of particle edge sites in methane activation and dehydrogenation.
TL;DR: The suitability of nanocarbons as catalysts for oxida-tive dehydrogenation (ODH) reactions has been investi-gated for numerous hydrocarbon substrates, such as ethylbenzene, 1-butene, isobutene, n-butane, and pro-pane as discussed by the authors.
Abstract: C-H activation; carbon nanotubes; dehydrogenation; oxidation; surface modification The suitability of nanocarbons as catalysts for oxida-tive dehydrogenation (ODH) reactions has been investi-gated for numerous hydrocarbon substrates, such as ethylbenzene, 1-butene, isobutene, n-butane, and pro-pane.