Robbie Warringham

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.

Vibrational Analysis of an Industrial Fe-Based Fischer–Tropsch Catalyst Employing Inelastic Neutron Scattering†

Inelastic neutron scattering (INS) has been used to obtain the vibrational spectrum of a technical-grade iron-based Fischer–Tropsch catalyst that has been taken from an industrial large-scale unit operation. Whereas previous reports on iron Fischer–Tropsch catalysts highlight the presence of retained carbonaceous species, the INS spectra reveal the additional presence of partially hydrogenated aromatic molecules.

Sample environment issues relevant to the acquisition of inelastic neutron scattering measurements of heterogeneous catalyst samples

Refinements to established sample handling issues connected with the acquisition of inelastic neutron scattering (INS) spectra of heterogeneous catalyst samples are described. This involves modification of a reactor and improvements to gas handling apparatus. The latter includes provision of laboratory space and ventilation facilities that are suited to the increasingly wide range of catalytic samples being examined. INS measurements for CO hydrogenation over an iron-based Fischer-Tropsch catalyst recorded using the MARI spectrometer are presented to illustrate the applicability of the new arrangements.

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.

Pore Topology Effects in Positron Annihilation Spectroscopy of Zeolites

Positron annihilation spectroscopy (PAS) is a powerful method to study the size and connectivity of pores in zeolites. The lifetime of positronium within the host material is commonly described by the Tao-Eldrup model. However, one of its largest limitations arises from the simple geometries considered for the shape of the pores, which cannot describe accurately the complex topologies in zeolites. Here, an atomic model that combines the Tao potential with the crystallographic structure is introduced to calculate the distribution and lifetime of Ps intrinsic to a given framework. A parametrization of the model is undertaken for a set of widely applied zeolite framework types (*BEA, FAU, FER, MFI, MOR, UTL), before extending the model to all known structures. The results are compared to structural and topological descriptors, and to the Tao-Eldrup model adapted for zeolites, demonstrating the intricate dependence of the lifetime on the pore architecture.