THE COADSORPTION OF ETHYLENE AND HYDROGEN ON PT(210), (1X1)PT(110), AND (2X1)PT(110)

Previous work has shown that the rate of ethylene hydrogenation on a hydrogen covered platinum surface is significantly different than the rate of ethylene hydrogenation on clean platinum. However, it is unclear why the difference in rate occurs. In this paper, the coadsorption of ethylene and hydrogen on (2X1)Pt(110), (1x1)Pt(110), and Pt(210) was examined using temperature programmed desorption (TPD) and electron energy-loss spectroscopy (EELS). It is found that adsorbed hydrogen substa ntially modifies the adsorption of ethylene. While ethylene adsorption on a clean 93 K (2 × 1 )Pt( 110) sample results in the production of a mixture of di-o and abound ethylene, little di-σ ethylene is observed if the sample is exposed to 100 L of H2 before the surface is exposed to ethylene. Instead, a new form of adsorbed ethylene is seen. The new form of adsorbed ethylene has a vibrational spectrum very similar to that of gas phase ethylene suggesting it is weakly bound. We also observe the weakly bound form of ethylene on (lXl)Pt(llO) and Pl(210). These results show that the adsorbed hydrogen significantly modifies the adsorption of ethylene on various platinum surfaces. © 1990, American Vacuum Society. All rights reserved.