Ethene Adsorption and Reactivity on Surfaces

This section describes the adsorption properties of ethene on the surfaces MgO lOO) and / t(lll), probed by means of TPD and EES. Additionally, with TPR the ethene self-/hydrogenation on Pt(l 11) is investigated. The surfaces properties and reactivity serve as control with respect to the literature and as a comparison for experiments on Ptn and Ptx clusters on AfgO(lOO) in the next section as well as for future studies. Hereby, the MgO(lOO) surface is used as inert support material [27, 57], whereas EtCl 11) is applied as a well known hydrogenation catalyst [58, 59]. 

Comparable TPD experiments (measurement on 28 m/z) of ethene interaction on MgO(lOO) and Pt(l 11) as a function of coverage were measured and are depicted in Fig. 4.26. 

The decrease in peak area for p (and the shift in peak maxima) can be explained by the known formation of carbon (Sect. 2.1.2) at temperatures above 450-500 K, which blocks active sites on the Pf(l 11) surfaces for chemisorption of ethene. With repeated TPD experiments, the surface gets more and more poisoned and thus shows 

A further proof of the presence of carbon on the surface is given by the AES results in Fig. 4.38 

This fact is not only a draw back, but was useful in clarifying, that ethene is adsorbed parallel on the surface with respect of its molecular plane [41]. 

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