THERMAL-ACTIVATION OF 3-BROMOCYCLOHEXENE ON PT(111)

The adsorption and thermal activation of 3-bromocyclohexene on Pt(111) was studied by temperature programmed desorption (TPD), high-resoluti on electron energy loss spectroscopy (HREELS), and X-ray photoelectron spectroscopy (XPS). Upon adsorption, the first layer of 3-bromocycloh exene dissociatively adsorbs to make Br-Pt and C6H9-Pt bonds and produ ces benzene upon thermal activation. At higher coverages, 3-bromocyclo hexene molecularly adsorbs and desorbs as the temperature increases, A t lower coverages, the second layer molecular desorption peak at 192 K is distinct from the multilayer desorption peak at 173 K, but as the total coverage grows, the second layer shifts into the multilayer. Fol lowing molecular desorption, C, symmetric pi-allylic C6H9 species rema in on the surface and are stable until 250 K, where they dehydrogenate to benzene; the dehydrogenation is rapidly completed by 280 K. Most o f the benzene desorbs above 300 K, but a small amount decomposes to Cx Hy species above 400 K to form surface carbide. The surface Br either captures H generated by the dehydrogenation and leaves the surface as HBr between 220 and 280 K or recombines as Br-2 above 500 K.