Scientific Highlights

15 November 2012

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DFT Modelling of Ru Nanoparticles Supported on Graphene and Graphite Surface: A Study of the B5 Active Sites Localisation

Carbon-supported Ruthenium catalysts exhibit very good catalytic properties, and are applied in the ammonia synthesis as well as for methanation processes e.g. in the gasification of wet biomass in super-critical water. Both reactions are known to be structure sensitive and require specific active sites at the catalyst. It has been found experimentally that mainly B5 sites are present and actively taking part in the catalytic reactions. Epitaxial growth of Ru on the carbon support can be considered following two orientations, one with the same orientation as the hexagonal carbon lattice, the other being rotated by 30° around the surface normal.

15 July 2012

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Supported gold as catalyst for the decomposition of ammonia precursors in the selective catalytic reduction of NOx

Titaniumdioxide supported gold was found to catalyze the hydrolysis of formate-based ammonia precursor compounds which are proposed for the selective catalytic reduction of nitrogen oxides (NOx) in combustion exhaust gas. In contrast to other noble metals, the supported gold does not oxidize the released NH3, while it maintains decomposition of intermediate formic acid.
---+!! Influence of Methyl Halide Treatment on Gold Nanoparticles Supported on Activated Carbon Gold particles supported on carbon when subjected to a flow of methyl iodide or bromide redisperse from large ensembles to single atoms and/or dimers of gold. Methyl halide oxidizes gold leading to gradual particle dissolution. The process could be carried out at temperatures as low as 50 °C. The excess of halide could be removed by a post-treatment of the material with 1%H2O/H2, which does not influence the metal dispersion. This remarkable transformation opens the possibility of re-activating gold catalysts that lost their performance due to metal particles sintering.

The finding was proposed based on a combination of in situ (XAS), ex situ characterization (aberration corrected HAADF-TEM, XRD and XPS) and kinetic measurements. The work was a combined effort from Queen’s University Belfast (UK), Paul Scherrer Institute (Switzerland), Lehigh University (USA) and Cardiff University (UK)

Presentation slides
Citation: J. Sá, A. Goguet, S. F. Rebecca Taylor, R. Tiruvalam, C. J. Kiely, M. Nachtegaal, G. J. Hutchings, C. Hardacre, Angew. Chem. Int. Ed. 50 (2011) 8912-8916.

Publication: http://dx.doi.org/10.1002/anie.201102066

Further publications: LBK Publications

15 July 2009

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Identification of the SCR active sites in Fe-ZSM-5

he identification of the SCR active sites in Fe-ZSM-5 is of utmost importance for the understanding and optimization of the catalyst performance. No method (e.g. UV/VIS, IR, EPR, EXAFS, XPS, XRD) can definitively distinguish between isolated iron species and iron oxide clusters of different nuclearity in the same sample. A statistical approach was used to solve this problem. From the correlation of the measured SCR activity with the calculated concentration of different species the temperature dependent activities of isolated, dimeric and oligomeric iron species and iron particles could be determined.

15 October 2007

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Vibrational Spectra of Adsorbates from DFT

The hydrolysis of isocyanic acid was studied experimentally and theoretically and a reaction mechanism on different catalysts was established. The decreasing NOx emission limits for diesel vehicles impel the further development of the existing NOx deactivation technologies, particularly the selective catalytic reduction (SCR) of nitrogen oxides with urea. In the urea-SCR process, urea is injected into the hot exhaust gas, where it thermally decomposes into isocyanic acid (HNCO) and ammonia.