Malcolm L. H. Green

Carbonhydrogen-transition metal bonds

Abstract Evidence that carbonhydrogen bonds may act as ligands to transition metal centres forming covalent CH⇀M systems in which, formally, the CH group donates two electrons to the metal is reviewed and consequences are discussed.

Agostic interactions in transition metal compounds

The impact of agostic interactions (i.e., 3-center–2-electron MHC bonds) on the structures and reactivity of organotransition metal compounds is reviewed.

Recent advances in the conversion of methane to synthesis gas

Abstract A brief review on the recent developments of alternative routes for synthesis gas production, namely catalytic methane partial oxidation and methane reforming with carbon dioxide, is presented. Particular attention is given to reaction thermodynamics, catalyst formulation, reaction mechanism and problems of carbon deposition.

Brief Overview of the Partial Oxidation of Methane to Synthesis Gas

A review of the main developments in the partial oxidation of methane to synthesis gas since the first paper in 1929 to the present day is given. The reaction is discussed from the view of the thermodynamics; the main catalysts studied for the reaction are summarised, and the reaction mechanism is discussed. The review is not comprehensive, but it is designed to provide a general background to the most important developments in the field.

Partial oxidation of methane to synthesis gas

Partial oxidation of methane to synthesis gas has been carried out over a number of transition metal catalysts under a range of conditions. It is found that the metals Ni, Ru, Rh, Pd, Ir and Pt, either supported on alumina or present in mixed metal oxide precursors, will bring the system to equilibrium. The yield of CO and H2 improves with increasing temperature in the range 650–1050 K, and decreases with increasing pressure between 1 and 20 atm. An excellent yield (∼92%) is obtained with a 4∶2∶1 N2∶CH4∶O2 ratio at 1050 K and atmospheric pressure, with a space velocity of 4×104 hour−1.

Nucleophilic addition to organotransition metal cations containing unsaturated hydrocarbon ligands : A survey and interpretation

Abstract Three simple rules are proposed that enable the prediction of the most favourable position of nucleophilic attack on 18 electron organotransition metal cations containing unsaturated hydrocarbon ligands.

A study of carbon deposition on catalysts during the partial oxidation of methane to synthesis gas

The deposition of carbon on catalysts during the partial oxidation of methane to synthesis gas has been investigated and it has been found that the relative rate of carbon deposition follows the order Ni>Pd>Rh>Ir. Methane decomposition was found to be the principal route for carbon formation over a supported nickel catalyst, and electron micrographs showed that both “whisker” and “encapsulate” forms of carbon are present on the catalyst. Negligible carbon deposition occurred on iridium catalysts, even after 200 h.

Filled and glycosylated carbon nanotubes for in vivo radioemitter localization and imaging

Functionalization of nanomaterials for precise biomedical function is an emerging trend in nanotechnology. Carbon nanotubes are attractive as multifunctional carrier systems because payload can be encapsulated in internal space whilst outer surfaces can be chemically modified. Yet, despite potential as drug delivery systems and radiotracers, such filled-and-functionalized carbon nanotubes have not been previously investigated in vivo. Here we report covalent functionalization of radionuclide-filled single-walled carbon nanotubes and their use as radioprobes. Metal halides, including Na(125)I, were sealed inside single-walled carbon nanotubes to create high-density radioemitting crystals and then surfaces of these filled-sealed nanotubes were covalently modified with biantennary carbohydrates, improving dispersibility and biocompatibility. Intravenous administration of Na(125)I-filled glyco-single-walled carbon nanotubes in mice was tracked in vivo using single-photon emission computed tomography. Specific tissue accumulation (here lung) coupled with high in vivo stability prevented leakage of radionuclide to high-affinity organs (thyroid/stomach) or excretion, and resulted in ultrasensitive imaging and delivery of unprecedented radiodose density. Nanoencapsulation of iodide within single-walled carbon nanotubes enabled its biodistribution to be completely redirected from tissue with innate affinity (thyroid) to lung. Surface functionalization of (125)I-filled single-walled carbon nanotubes offers versatility towards modulation of biodistribution of these radioemitting crystals in a manner determined by the capsule that delivers them. We envisage that organ-specific therapeutics and diagnostics can be developed on the basis of the nanocapsule model described here.

Partial oxidation of methane to synthesis gas, and carbon dioxide as an oxidising agent for methane conversion

Abstract The partial oxidation of methane by oxygen giving synthesis gas can be catalysed to thermodynamic equilibrium using the transition metals Ni, Ru, Rh, Pd, Pt and Ir supported on inert oxides. The yield of CO and H 2 increases with increase in temperature (650 – 1050K) and decreases with increasing pressure from 1 to 20 atm. The gas mixture N 2 : CH 4 : O 2 at the ratio 4:2:1 at 1050K and 1 atmosphere with a space velocity of 4 × 10 4 hour −1 gives an −92% yield of synthesis gas. Under similar conditions of temperature and pressure we show that catalysts such as iridium on alumina are also active for the combined partial oxidation and carbon dioxide reforming reaction giving synthesis gas in similarly high yield.

Methane Oxyforming for Synthesis Gas Production

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.