Non-thermal plasma activated catalysis for low temperature operation
Professor Chris Hardacre, University of Manchester, UK
Hybrid non-thermal plasma catalysis has a significant potential to provide a low energy pathway to activate molecules and catalysts to enable processes to operate at lower temperatures than would occur if activated thermally. This presentation will show how plasma activation can be utilised to promote the water gas shift reaction, deNOx reactions and methane combustion. The role of the plasma will be explored and the mechanism of thermal vs plasma activated processes will be shown.
Alkane partial oxidation using dioxiranes in solution at low temperatures
Dr Sara Yacob, Exxon Mobil, USA
Direct catalytic partial oxidation of alkanes, such as methane, in the gas phase can often require high temperatures for activation of the strong aliphatic C–H bond. High temperature reaction conditions can frequently lead to gas phase radical reactions, with intrinsically low selectivity and poor control of yields. However, partial oxidation catalysts capable of efficiently operating at low temperatures may limit the over-oxidation of the alkane substrate and thereby improve selectivity. Frequently, when supported transition metal catalysts are used for C–H bond activation, irreversible deactivation via metal reduction, particle sintering, or coke deposition is observed. Therefore, this study focuses on examining alkane oxidation using completely metal-free organocatalysts, dioxiranes, in solution at low temperatures. Typical dioxiranes, such as dimethyldioxirane and methyl(trifluoromethyl)dioxirane, can be prepared by oxidation of the parent ketone so that the dioxirane can be added as isolated species, however, in this manner the dioxirane serves only as a stoichiometric oxidant. This work aims to generate dioxirane in situ so that the process can be catalytic with respect to the ketone using H2O2 as the stoichiometric oxidant.
TiO2 and ZrO2 in biomass conversion: why catalyst reduction helps
Professor Gianfranco Pacchioni, University of Milano-Bicocca, Italy
Reducible oxides are considered to be more active than non-reducible oxides in catalytic conversion of biomass to biofuels, but the reasons are unclear and are the object of this talk. The properties of anatase TiO2 and tetragonal ZrO2 (101) surfaces have been studied using DFT+D calculations with inclusion of dispersion forces. The attention is on the role of surface reduction, either by creation of oxygen vacancies, or by treatment in hydrogen. The presence of reduced centers on the surface of titania or zirconia (either Ti3+ or Zr3+ ions or oxygen vacancies) results in lower barriers and more stable intermediates in two key reactions in biomass catalytic conversion: ketonization of acetic acid and deoxygenation of phenol. The role of supported Ru nanoparticles is also considered. They favour H2 dissociation and hydrogen spillover, resulting in hydroxylated surfaces. H2O desorption from the hydroxylated surfaces may be a relevant mechanism for the regeneration of oxygen vacancies, in particular on low-coordinated sites of oxide nanoparticles. Finally, the role of nanostructuring on oxide reduction is discussed. ZrO2 nanoparticles of diameter of about 2 nm have completely different behaviour compared to the bulk oxide, and are much more reducible. Nanostructured zirconia has a similar behaviour as titania.
A deeper understanding of structured Co-Fischer Tropsch Synthesis catalysts via chemical tomography
Professor Andy Beale, University College London, UK
The imaging of catalysts under reaction conditions has advanced significantly in recent years. The combination of the computed tomography (CT) approach with methods such as X-ray diffraction (XRD), X-ray fluorescence (XRF), and X-ray absorption near edge spectroscopy (XANES) now enables local chemical and physical state information to be extracted from within the interiors of materials which are, by accident or design, inhomogeneous. The spatially resolved signals obtained reveal information otherwise lost in bulk measurement. Studying intact materials rather than idealised powders allows for behaviour under industrially relevant conditions to be observed. Such methods have been applied to study catalytic systems over a range of length scales (from ~1 µm to 10 mm). On small length scales (<200 µm), X-ray transmission at ‘low’ energies (<10 keV) is possible and allows for performing multi-modal imaging (i.e. combined spectroscopic and diffraction imaging) on packed-bed micro-reactors (Co/SiO2 FTS catalysts) enabling for a more inclusive correlation of catalyst composition with performance. On larger length scales (i.e. >few mm) high energy scattering computed-CT enables large/dense objects to be studied i.e. 3 mm Co/g-Al2O3 pellets. This information is vital to rational catalyst and reactor design that cannot be obtained by conventional bulk measurements.