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Open Access Spectroscopic Detection of Active Species on Catalytic Surfaces: Steady-State versus Transient Method

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Discrimination between active and spectator species is an important and demanding task in catalysis research. A comparative study of the Pd-catalyzed CO hydrogenation using in situ diffuse reflectance IR Fourier transform spectroscopy (DRIFTS) in steady-state and dynamic (transient) experiments shows that the information on surface species differs significantly depending on the type of experiment. In order to discriminate between active species and spectator species not involved in the surface reactions, DRIFTS was combined with a transient technique, modulation excitation spectroscopy (MES). This approach allows the detection of surface species responding to a specific periodic external stimulus, i.e.achieved by concentration modulation, and thereby offers excellent potential to unveil features of the surface processes, which are not accessible by steady-state experiments. However, the example of CO hydrogenation shows that the perturbation imposed to the system has to be chosen properly to benefit from the transient technique. Modulation of the CO concentration did not provide deeper insight into the reaction mechanism, whereas periodic changes of the hydrogen concentration provided valuable information concerning the active surface species and the reaction pathway. The study revealed that only a small fraction (about 4%) of CO molecules adsorbed on specific Pd sites reacted with hydrogen, while the majority of adsorbed CO was inactive. The inactive CO molecules overwhelmingly contributed to the spectra measured under steady-state conditions.

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Document Type: Research Article

Affiliations: 1: Institute for Chemical and Bioengineering Department of Chemistry and Applied Biosciences ETH Zurich, Wolfgang-Pauli-Strasse 10 CH-8093 Zürich, Switzerland 2: Institute for Chemical and Bioengineering Department of Chemistry and Applied Biosciences ETH Zurich, Wolfgang-Pauli-Strasse 10 CH-8093 Zürich, Switzerland; Chemistry Department, Faculty of Science, King Abdulaziz University, P.O. Box 80203, Jeddah 21589, Saudi Arabia. [email protected]

Publication date: September 1, 2012

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  • International Journal for Chemistry and Official Membership Journal of the Swiss Chemical Society (SCS) and its Divisions

    CHIMIA, a scientific journal for chemistry in the broadest sense, is published 10 times a year and covers the interests of a wide and diverse readership. Contributions from all fields of chemistry and related areas are considered for publication in the form of Review Articles and Notes. A characteristic feature of CHIMIA are the thematic issues, each devoted to an area of great current significance.

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