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Krick Calderon S.,Friedrich - Alexander - University, Erlangen - Nuremberg | Grabau M.,Friedrich - Alexander - University, Erlangen - Nuremberg | Ovari L.,MTA SZTE Reaction Kinetics and Surface Chemistry Research Group | Kress B.,Friedrich - Alexander - University, Erlangen - Nuremberg | And 3 more authors.
Journal of Chemical Physics | Year: 2016

The oxidation of CO on Pt(111) was investigated simultaneously by near ambient pressure X-ray photoelectron spectroscopy and online gas analysis. Different CO:O2 reaction mixtures at total pressures of up to 1 mbar were used in continuous flow mode to obtain an understanding of the surface chemistry. By temperature-programmed and by isothermal measurements, the onset temperature of the reaction was determined for the different reactant mixtures. Highest turnover frequencies were found for the stoichiometric mixture. At elevated temperatures, the reaction becomes diffusion-limited in both temperature-programmed and isothermal measurements. In the highly active regime, no adsorbates were detected on the surface; it is therefore concluded that the catalyst surface is in a metallic state, within the detection limits of the experiment, under the applied conditions. Minor bulk impurities such as silicon were observed to influence the reaction up to total inhibition by formation of non-platinum oxides. © 2016 AIP Publishing LLC. Source

Bajus S.,Friedrich - Alexander - University, Erlangen - Nuremberg | Agel F.,Friedrich - Alexander - University, Erlangen - Nuremberg | Kusche M.,Friedrich - Alexander - University, Erlangen - Nuremberg | Ni Bhriain N.,Friedrich - Alexander - University, Erlangen - Nuremberg | And 2 more authors.
Applied Catalysis A: General | Year: 2016

We herein present an easy approach to increase drastically the catalytic activity of Ru/γ-Al2O3 catalysts in ammonia decomposition by surface modification with alkali hydroxides. The best activities have been achieved by a catalyst modification with lithium hydroxide in a Li/Al ratio of 1.7. In contrast, coatings with potassium and caesium hydroxide caused mass transfer limitations in the catalytic material already at low amounts (ratios alkali/Al <0.2-0.3). MAS ssNMR and XRD studies indicate the in-situ formation of alkali aluminates resulting in a basic modification of the support. © 2015 Elsevier B.V. Source

Papp C.,Friedrich - Alexander - University, Erlangen - Nuremberg | Wasserscheid P.,Friedrich - Alexander - University, Erlangen - Nuremberg | Wasserscheid P.,Erlangen Catalysis Resource Center | Libuda J.,Friedrich - Alexander - University, Erlangen - Nuremberg | And 3 more authors.
Chemical Record | Year: 2014

We review recent results towards a molecular understanding of the adsorption and dehydrogenation of carbazole-derived liquid organic hydrogen carriers on platinum and palladium single crystals and on Al2O3-supported Pt and Pd nanoparticles. By combining synchrotron-based high-resolution X-ray photoelectron spectroscopy, infrared reflection-absorption spectroscopy, advanced molecular beam methods and temperature-programmed desorption spectroscopy, detailed insights into the reaction mechanism are obtained. On Pt(111), dehydrogenation of perhydro-N-ethylcarbazole, H12-NEC, starts with activation of the hydrogen atoms at the pyrrole unit, yielding H8-NEC as the first stable reaction intermediate at ∼340 K, followed by further dehydrogenation to NEC at ∼380 K. Above 390 K, dealkylation starts, yielding carbazole as an undesired byproduct. On small supported Pt particles, the dealkylation sets in at lower temperatures, due to the higher reactivity of low-coordinated sites, while on larger particles with (111) facets a reactivity as on the flat surface is observed. Carbazole derivatives with ethyl, propyl and butyl chains show an overall very similar reactivity, both on Pt(111) and on Pt nanoparticles. When comparing the dealkylation behavior of H12-NEC on Pt(111) and Pt nanoparticles to that on Pd(111) and Pd nanoparticles, we find a higher reactivity for the Pd systems. © 2014 The Chemical Society of Japan and Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

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