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XPS-UPS Systems

XPS/UPS systems are a standard tool for the characterization of the chemical composition and the electronic structure of the surfaces of solids. Often a preparation chamber is integrated, so that samples inserted through the Load Lock chamber can be cleaned before analysis. Integration of sputter depth profiling, Auger electron spectroscopy, (R)EELS or Ion scattering spectroscopy is easily possible in the measurement position to get a more holistic insight into the properties of the samples.By using small spot sources, a 2D-detector and stage mapping, chemical mapping of the surface is possible, as well, to characterize the inhomogeneous element distribution on technical sample surfaces.



  1. (2017) Catalytic consequences of Ga promotion on Cu for CO2 hydrogenation to methanol

    The promotion of Ga on SiO2 supported Cu in the hydrogenation of CO2 to methanol at 800 kPa and 200–280 °C was investigated. Cu/SiO2 and CuGa/SiO2 catalysts were prepared by a water-in-oil microemulsion technique resulting in Cu clusters of 4–6.5 nm. It was found that Ga addition increased the methanol formation rate by an order of magnitude without significantly changing that for reverse water gas shift (RWGS). This trend is also evidenced by the decrease in the apparent activation barrier for methanol formation from 78 (for Cu/SiO2) to 26–39 kJ mol−1 when Ga was added, but not for RWGS (107–132 kJ mol−1). Kinetic and in situ DRIFTS analyses revealed that formate intermediates are adsorbed on both Cu and Ga2O3 and that methoxy hydrogenation could be the rate determining step of methanol synthesis. In the case of RWGS, a zero order of CO formation with respect to H2 concentration was consistent with a redox mechanism and with the reaction occurring predominantly on Cu sites. The results suggest that Ga promotes Cu increasing methanol selectivity, likely by creating new active sites for methanol formation without modifying its oxidation state, which under reaction conditions remains mostly metallic.

    J. C. Medina, M. Figueroa, R. Manrique, J. R. Pereira, P. D. Srinivasan, J. J. Bravo-Suárez, V. G. Baldovino Medrano, R. Jiméneza and A. Karelovic
    Catal. Sci. Technol., 2017,7, 3375-3387
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  2. (2019) Insights into the role of Zn and Ga in the hydrogenation of CO2 to methanol over Pd

    The hydrogenation of CO2 to methanol is a viable alternative for reducing greenhouse gases net emissions as well as a route for hydrogen storage and transportation. In this context, the synthesis of active and selective catalysts is a relevant objective. In this work, we study the promotion of Pd with Ga and Zn in the hydrogenation of CO2 to methanol at 800 kPa and 220–280 °C. Mono and intermetallic catalysts (Pd/SiO2, PdGa/SiO2 and Pd-Zn/SiO2) were synthesized by incipient wetness impregnation with the aid of triethanolamine as an organic additive, obtaining similar average metal particle sizes (between 9 and 12 nm). Kinetic analysis reveals that the addition of Ga and Zn increases the turnover frequency for methanol formation by an order of magnitude without significant changes in the reaction rate of the reverse water-gas shift (r-WGS) which is a parallel undesired reaction. The selectivity to methanol (at 220 °C) thus increases from 3% for Pd/SiO2 to 12% for Pd-Ga/SiO2 and 30% for Pd-Zn/SiO2. XPS studies, Infrared analysis of CO adsorption, and XRD analyses show the presence of intermetallic phases Pd2Ga and PdZn on the surface. The results suggest that Ga and Zn promote Pd, increasing its activity towards the synthesis of methanol, by creating more active sites for this reaction. These sites are likely formed by intermetallic compounds such as Pd2Ga and PdZn.

    R. Manrique, R. Jiménez, J. Rodríguez-Pereira, V. G. Baldovino-Medrano, and A. Karelovic
    International Journal of Hydrogen Energy, Volume 44, Issue 31, 21 June 2019, Pages 16526-16536
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