Adsorption and thermal decomposition of ethylbenzene and styrene on Pt(111) studied by UPS and XPS

The interaction of ethylbenzene (EB) and styrene with Pt(111) was studied by UPS and XPS for adsorption temperatures between 135 and 870 K. Below 350 K, styrene chemisorbs strongly and the work function decreases by more than 2 eV indicating strong polarization or charge transfer. This is accompanied by different bonding shifts of the π and σ orbitals towards lower binding energy. After saturation of the chemisorbed layer, physisorption and finally condensation in the form of clusters is observed. The isosteric heats of adsorption for physisorbed and condensed styrene are 61 and 58.5 kJ mol−1, respectively. The first EB layer dissociates into chemisorbed styrene and hydrogen atoms. The subsequent physisorbed and condensed layers consist of undissociated EB. Upon annealing in an EB or styrene atmosphere, chemisorbed γ-styrene polymerizes at about 400 K with a saturation coverage slightly above one monolayer. Upon further annealing the layer starts to decompose and beyond 700 K it forms a graphitic coke layer. Annealing of a γ-styrene layer without further gas admission yields the same species but with lower coverages.