Determination of Decomposition Starting Temperature of Hydrocarbons Adsorbed on a Single Crystal Surface: Representative Results for Cycloheptane on Ni(755)

H. Orita, H. Kondoh, and H. Nozoye
[J. Phys. Chem., Vol.99(11), pp.3648-3654, 1995]

The method to determine the decomposition starting temperature (the temperature where a molecule starts to decompose) of hydrocarbons adsorbed on a single crystal surface was developed by taking use of inhibiting effect of CO on the decomposition. The representative results for cycloheptane decomposition on Ni(755) have been presented. Temperature programmed desorption (TPD) spectra after pre-flash and postdosing of CO (Fig. 1) indicates that the decomposition of adsorbed cycloheptane to partially dehydrogenated intermediates starts from 162 K and is completed by 200 K. The characteristics and differences in predosing and postdosing effects between CO and bismuth have been discussed.

Fig. 1. Variations in TPD peak areas of hydrogen and CO normalized to surface nickel atoms with pre-flash temperature. Cycloheptane was predosed at 123 K for 80 s (c-C₇/Ni= 0.029) and the surface was flashed at 10 K/s to a desired temperature (pre-flash temperature). After recooling to 123 K, CO was postdosed to the surface for 50 s and the a TPD was measured.