Andrew R. McFarlane

Experimental arrangements suitable for the acquisition of inelastic neutron scattering spectra of heterogeneous catalysts

Inelastic neutron scattering (INS) is increasingly being used for the characterization of heterogeneous catalysts. As the technique is uniquely sensitive to hydrogen atoms, vibrational spectra can be obtained that emphasize a hydrogenous component or hydrogen-containing moieties adsorbed on to an inorganic support. However, due to sensitivity constraints, the technique typically requires large sample masses (∼10 g catalyst). A reaction system is hereby described that enables suitable quantities of heterogeneous catalysts to be appropriately activated and operated under steady-state conditions for extended periods of time prior to acquisition of the INS spectrum. In addition to ex situ studies, a cell is described which negates the need for a sample transfer stage between reaction testing and INS measurement. This cell can operate up to temperatures of 823 K and pressures up to 20 bar. The apparatus is also amenable to adsorption experiments at the gas-solid interface.

The application of inelastic neutron scattering to investigate the ‘dry’ reforming of methane over an alumina-supported nickel catalyst operating under conditions where filamentous carbon formation is prevalent

The use of CO2 in reforming methane to produce the industrial feedstock syngas is an economically and environmentally attractive reaction. An alumina-supported nickel catalyst active for this reaction additionally forms filamentous carbon. The catalyst is investigated by inelastic neutron scattering as well as elemental analysis, temperature-programmed oxidation, temperature-programmed hydrogenation, X-ray diffraction, transmission electron microscopy and Raman scattering. Isotopic substitution experiments, using 13CO2 for 12CO2, show the oxidant to contribute to the carbon retention evident with this sample. At steady-state operation, a carbon mass balance of 95% is observed. A kinetic scheme is proposed to account for the trends observed.

Continuous catalytic upgrading of fast pyrolysis oil using iron oxides in red mud

A catalyst composed primarily of magnetite was prepared from red mud, via H2 reduction at 300 °C, which significantly increased the surface area. Ammonia and CO2 temperature programmed desorption indicated both acid and base active sites. Continuous reaction studies conducted with individual compounds, mixtures of model compounds, and water extracted fast pyrolysis oil indicated that acetone was the primary product from acetic acid, and acetone and 2-butanone from acetol. Levoglucosan went down the same pathway, since it formed acetic acid, formic acid, and acetol. Total conversion and yields approached 100% and 22 mol% ketones at 400 °C and a W/F of 6 h for a model mixture and 15–20 mol% ketones at W/F 1.4–4 h and 400–425 °C using water extracted oil. Space time yields approached 60 g ketones per L-cat per h for the model mixture and 120 g per L-cat per h for a commercial oil. The catalyst simultaneously reduced acidity, allowed recovery of carbon, and generated upgradable intermediates from the aqueous fraction of fast pyrolysis oil in a “continuous” process.

The application of inelastic neutron scattering to explore the significance of a magnetic transition in an iron based Fischer-Tropsch catalyst that is active for the hydrogenation of CO

An iron based Fischer-Tropsch synthesis catalyst is evaluated using CO hydrogenation at ambient pressure as a test reaction and is characterised by a combination of inelastic neutron scattering (INS), powder X-ray diffraction, temperature-programmed oxidation, Raman scattering, and transmission electron microscopy. The INS spectrum of the as-prepared bulk iron oxide pre-catalyst (hematite, α-Fe2O3) is distinguished by a relatively intense band at 810 cm(-1), which has previously been tentatively assigned as a magnon (spinon) feature. An analysis of the neutron scattering intensity of this band as a function of momentum transfer unambiguously confirms this assignment. Post-reaction, the spinon feature disappears and the INS spectrum is characterised by the presence of a hydrocarbonaceous overlayer. A role for the application of INS in magnetic characterisation of iron based FTS catalysts is briefly considered.

The carbon deposits formed by reaction of a series of red mud samples with methanol

Magnetic carbon materials were prepared by the catalytic growth of graphitic carbon and carbon nanofibers using methanol as a carbon source with a series of different red mud wastes. Both the raw red mud samples and the products were characterized using powder X-ray diffraction, scanning electron microscopy, Raman spectroscopy, Brunaeur Emmett and Teller surface area analysis, thermogravimetric analysis and carbon content analysis. Hematite and goethite in high iron content red muds were reduced into magnetite in 10 minutes at 500 °C, and graphitic carbon reflections were evident in the resultant powder X-ray diffraction pattern. Thus, the samples become magnetic and change color from red to black. After six hours reaction at 500 °C, the carbon content of the composite based on a high iron content Bayer process derived red mud reached as high as ca. 72% and its surface area increased from 17 to 312 m2 g−1.