X-ray photoelectron spectroscopy and heterogeneous catalysis, with elimination reactions as an example

Abstract

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.