Showing papers by "Malcolm L. H. Green published in 2007"
TL;DR: The impact of agostic interactions (i.e., 3-center–2-electron MHC bonds) on the structures and reactivity of organotransition metal compounds is reviewed.
Abstract: The impact of agostic interactions (i.e., 3-center-2-electron M-H-C bonds) on the structures and reactivity of organotransition metal compounds is reviewed.
878 citations
TL;DR: The majority of carboxylic acid groups formed after treatment of a single-walled carbon nanotube (SWCNT) material with nitric acid are present on carboxylated carbonaceous fragments (CCFs).
Abstract: The majority of carboxylic acid groups formed after treatment of a single-walled carbon nanotube (SWCNT) material with nitric acid are present on carboxylated carbonaceous fragments (CCFs) (see figure). These CCFs are removed from the SWCNTs by treatment with NaOH solution and identified as carriers of the COOH functionality, implying that previous reports claiming side-wall functionalization of the SWCNTs with COOH groups should be reconsidered.
258 citations
TL;DR: A review of the steam reforming Rxn is presented, and the dry reforming and partial oxidation Rxns introduced in this article, along with a background to oxyforming, industrial practice, and some of the most important latest developments.
Abstract: This article is concerned with the reforming of methane to synthesis gas; a review of the steam reforming Rxn is presented, and the dry reforming and partial oxidation Rxns introduced. Collectively, these processes are known as “oxyforming.” A background to oxyforming, industrial practice, and some of the most important latest developments will be presented, along with a section on the uses of synthesis gas. The current understanding of the Rxn mechanisms for the three processes and the problem of deactivation by carbon deposition will be discussed in detail. Finally, the economics of synfuel production will be addressed and compared with the production of other fuels, and the future directions and outlook for oxyforming will be forwarded. This article should allow the reader to make comparisons between these three important industrial reactions.
207 citations
TL;DR: In this article, a simplified ODS catalytic system composed of Na2WO4, 30% H2O2 and CH3CO2H was found suitable for the deep removal of sulfur in diesel.
Abstract: A simplified oxidative desulfurizataion (ODS) catalytic system composed of Na2WO4, 30% H2O2 and CH3CO2H has been found suitable for the deep removal of sulfur in diesel. By combining ODS and methanol extraction, the sulfur level in a commercial diesel has been reduced from 1100 ppm to 40 ppm. Treatment of model solutions of octane containing dibenzothiophene and 4,6-dimethyl dibenzothiophene with our ODS system shows 100% conversion of the thiophenes to sulfones at 70 8C in less than 1 h. # 2007 Elsevier B.V. All rights reserved.
194 citations
09 Mar 2007
TL;DR: In this paper, the agostic C-H-M bond was introduced to discuss the various manifestations of covalent interactions between carbon-hydrogen groups and transition metal centers in organometallic compounds.
Abstract: Carbon-hydrogen bonds, especially those of saturated (s$) carbon centres, are normally regarded as being chemically inert. Generally, the C-H group is not thought of as a potential ligand which can have a structural role or play an energetically significant part in ground states or in reaction intermediates. In this article we review recent observations which show that there are in fact many circumstances in which a carbon-hydrogen group will interact with a transition metal centre with formation of a two-electron three-centre bond and that the extent of the interaction is such as to have a marked effect on the molecular and electronic structure and hence reactivity of the molecule. We propose the term “agostic” which will be used to discuss the various manifestations of covalent interactions between carbon-hydrogen groups and transition metal centres in organometallic compounds l . The word agostic will be used to refer specifically to situations in which a hydrogen atom is covalently bonded simultaneously to both a carbon atom and to a transition metal atom. The agostic C-H-M bond is similar to the familiar and long known bridging hydrogen systems which occur in B-H-B, M-H-M, and B-H-M groups. The C-H-M bonds are a recent observation but as will be discussed below, they are probably very much more common than hitherto suspected. Since carbon-hydrogen bonds are a ubiquitous feature of organometallic compounds we have found it useful to define
158 citations
TL;DR: The sidewall functionalisation of carbon nanotubes using the standard nitric acid treatment can be greatly enhanced by first removing the amorphous carbon present in the sample.
116 citations
TL;DR: It was shown that SP-A and SP-D selectively bind to carbon nanotubes, and the binding was Ca 2+ -ion dependent, and was variable between batches of nanot tubes, so it was likely to be mediated by surface impurities or chemical modifications of the Nanotubes.
98 citations
TL;DR: Aqueous dispersions of single wall carbon nanotubes (C-SWNTs), prepared using different dispersing agents, have been analysed by Raman spectroscopy as discussed by the authors.
63 citations
TL;DR: This method, in conjunction with direct-Staudinger ligation of glycosyl azides to surface carboxylates allowed precise incorporation of glycans to the surface of SWNTs, allowing site-selective radiolabeling and demonstrating utility of these glyco-SWNTs as potential probes.
Abstract: Single-walled carbon nanotubes (SWNTs) functionalized with organic molecules bearing high-scattering element tags have allowed direct visualization of modification on the atomic scale. The inclusion of these tags in protecting groups allowed their subsequent removal and reincorporation to allow visualization of corresponding protection and deprotection of organic molecules on the SWNT. This method, in conjunction with direct-Staudinger ligation of glycosyl azides to surface carboxylates allowed precise incorporation of glycans to the surface of SWNTs. Resulting glyco-SWNTs interacted successfully with carbohydrate-active enzymes for the first time, allowing elaboration of the carbohydrate structure on the surface of the SWNT and demonstrating utility of these glyco-SWNTs as potential probes. Moreover, the glycosyltransferase-catalyzed transfer of [6-3H]-d-galactosyl to the surface of the SWNT allowed site-selective radiolabeling.
59 citations
TL;DR: In this article, the authors compared the performance of Co-Mo carbide and Co-Ni-W carbide catalysts and found that the CoWC x bimetallic catalyst was more active than Ni-containing catalysts.
Abstract: In this contribution the HDN catalytic behaviour of Co-Mo carbide catalysts and Co(Ni)-W carbide catalysts is compared in order to establish a rational effect of cobalt (or nickel) over Mo and W carbide HDN catalysts. The bimetallic and trimetallic catalysts were characterized by using elemental analysis, X-ray diffraction (XRD), infrared spectroscopy, Raman spectroscopy, thermo-gravimetric analysis and measurements of BET specific surface area. The catalytic performance was evaluated in a continuous flow reactor using hydrodenitrogenation of pyridine as model reaction. The incorporation of cobalt onto the structure of Mo 2 C reached an optimal Co/Mo ratio of 0.43 (i.e. Co 4 Mo 6 C x catalyst), whose HDN activity and stability was markedly higher than industrial catalysts (i.e. CoMoS/Al 2 O 3 and NiMoS/Al 2 O 3 ). Higher molar ratios facilitated the segregation of promoter. This was reflected in a poor catalytic stability not only on Co-Mo carbide catalysts, but also on the Co(Ni)-W carbide catalysts. The CoWC x bimetallic catalyst was more active in the steady state than Ni-containing catalysts. Two modes of pyridine adsorption may occur in the HDN reaction, the end-on mode appears to be the more favourable at low temperatures whereas the side-on mode is more favourable at higher temperatures. Further increasing reaction temperature over 400 °C leads to an increase in the hydrogenolysis reaction so more methane is produced, while the percentage of other hydrocarbon products decreased.
52 citations
TL;DR: In this paper, the polypeptides poly-l-(Trp,Lys·HBr) (Trp/Lys ·HBr = n/m) and polypoly(Tyr, Lys·Hbr) (Tyr/Ly·HBR = n /m) were tested as dispersing agents for single-wall carbon nanotubes (SWCNTs) for n/(n+m) values of 0, 0.2, and 1.5.
Abstract: The polypeptides poly-l-(Trp,Lys·HBr) (Trp/Lys·HBr = n/m) and poly-l-(Tyr,Lys·HBr) (Tyr/Lys·HBr = n/m) were tested as dispersing agents for single-wall carbon nanotubes (SWCNTs) for n/(n+m) values of 0, 0.2, and 1. Best results were obtained for the two copolymers, illustrating the importance of using amphiphilic dispersing agents. The dispersion effect is 3.5 times higher for the copolymer containing tryptophan, indicating a stronger interaction of the tryptophan residue with the SWCNTs compared to tyrosine. The degrees of debundling of the SWCNTs and the apparent binding of the polypeptides with the SWCNTs are analyzed by atomic force microscopy for the different dispersions. The interactions of the aromatic amino acid residues with the SWCNTs are further probed by using optical absorbance and fluorescence spectroscopy.
TL;DR: In this paper, the packing structure of bundled MoSI nanowires is investigated using scanning and high-resolution transmission electron microscopy to determine both the nanowire structure and bundle superstructure.
Abstract: The packing structure of bundled MoSI nanowires is investigated. Scanning and high-resolution transmission electron microscopy are used to determine both the nanowire structure and bundle superstructure. Shown is a high-resolution microscopy image of a small bundle. The image width is 8 nm. It is found that the nanowires pack in crystalline bundles defined by the P1 (#2) spacegroup.
TL;DR: In this article, the impact of agostic interactions (i.e., 3-center-2-electron M-H-C bonds) on the structures and reactivity of organotransition metal compounds is reviewed.
Abstract: The impact of agostic interactions (i.e., 3-center-2-electron M-H-C bonds) on the structures and reactivity of organotransition metal compounds is reviewed.
TL;DR: In this article, the authors describe a strategy for fabricating devices on perforated silicon nitride membranes that is ideal for systems with modulated structure, in particular for nanotubes with endohedral inorganic compounds or molecules.
Abstract: We describe a strategy for fabricating devices on perforated silicon nitride membranes that is ideal for systems with modulated structure, in particular for nanotubes with endohedral inorganic compounds or molecules, or nanotubes externally functionalized with soft materials. It uses dynamic nanostenciling and focussed ion beam while avoiding nanotubes’ exposure to chemicals or beams. Physical properties and high resolution transmission electron microscopy are then correlated. Devices with individual single-walled carbon nanotubes partially filled with potassium iodide (KI) showed negative differential resistance (NDR). We attribute the NDR to electrostatic potential modulation on the nanotube due to permanent dipoles in the KI chain.
TL;DR: Vapour synthesis is the use, as reagents, of vapours which are formed at high temperatures as discussed by the authors, typically, vapours such as those of transition metal atoms are brought into contact on a cold surface with a substrate, for example an unsaturated hydrocarbon.
Abstract: Vapour synthesis is the use, as reagents, of vapours which are formed at high temperatures. Typically, vapours, such as those of transition metal atoms, are brought into contact on a cold surface with a substrate, for example an unsaturated hydrocarbon. The ensuing reaction can form compounds, typically organo-transition metal complexes. The principles and methodology are discussed critically to show the applicability of this technique to synthesis and research. A review of recent research illustrating the scope of vapour synthesis is given.
TL;DR: A number of ruthenaborane clusters have been prepared containing the {(η-C5Me5)Ru(PMe3)} fragment as mentioned in this paper, containing the fragment.
04 May 2007
TL;DR: In this paper, a modification of the band structure of single-walled carbon nanotubes (SWNTs) through encapsulation of the inorganic material manganese ditelluride (MnTe2) is reported.
Abstract: Modification of the band structure of single‐walled carbon nanotubes (SWNTs) through encapsulation of the inorganic material manganese ditelluride (MnTe2) is reported. We show that this leads to a global reduction of their 1st (E11S) and 2nd (E22S) band gap energies by a similar percentage (up to 3.8%) and interpret this as due to a lowering of the carbon‐carbon transfer integrals.
TL;DR: In this article, a simple one-pot reaction between FeCl2, PMe3, C5R5H (R = H, Me) and Na/Hg in thf.
05 Jan 2007