Browsing by Author "Ebel, Maria"

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    Correlation between Results of X-ray Photoelectron Spectroscopic Studies and Catalytic Behaviour of MgO
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (08), 1978) Vinek, Hannelore; Latzel, Johannes; Noller, Heinrich; Ebel, Maria
    Different MgO samples were investigated by means of X-ray photoelectron spectroscopy and catalytic, desorption and basicity measurements. The O 1s peak of MgO showed a shoulder (or was split into two peaks) as a function of storage time. This shoulder and the second peak were identified as oxygen atoms of Mg(OH)2 with a binding energy of 531.5 ± 0.3 eV, compared with 529.9 ± 0.3 eV for pure MgO. In desorption measurements, only one H2O peak at ≈ 373 K was found with a freshly prepared MgO sample, whereas the other samples showed two peaks, one at ≈ 373, the other at 573 K. These experiments demonstrated the formation of a hydroxide layer on MgO with increasing storage time. With the growth of the hydroxide layer the basicity of the MgO samples decreased. The dehydrogenation and dehydration of butan-2-ol was used as test reaction. With increasing hydroxide layer and decreasing basicity the selectivity changed from dehydrogenation to dehydration.
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    X-ray photoelectron spectroscopy and heterogeneous catalysis, with elimination reactions as an example
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1977, 73 (05), 1977) Vinek, Hannelore; Noller, H.; Ebel, Maria; Schwarz, K.
    Assuming that the EPA and EPD strength of catalytically active surface sites is the major factor responsbile for catalytic properties, XPS is shown to be a powerful tool for estimating this factor and for predicting (or interpreting) the activity and selectivity of catalysts. This is illustrated with examples taken from elimination reactions. The dehydration activity of MgHPO4 is higher than that of MgSO4, corresponding to the higher Mg 2p binding energy and hence higher EPA strength of Mg. The selectivity of oxides for production of terminal olefins from alkan-2-ols, and for dehydrogenation, is related to a high EPD strength of oxygen (low 1s binding energy). The tendency of spinels to an E2 mechanism is higher than that of alumina, in accordance with the higher Al 2p binding energy and hence higher EPA strength in alumina. In zeolites, the high EPA strength of the exchangeable cations must be considered a decisive factor in the high catalytic activity.