APPLICATIONS OF BPTDS IN THE KINETICS AND MECHANISMS OF HYDROCARBON CONVERSION REACTIONS ON PT(111) - METHYLCYCLOHEXANE DEHYDROGENATION

Bismuth Postdosing Thermal Desorption Spectroscopy (BPTDS) and the rel ated D-2-BPTDS are mass spectroscopic techniques for quantitative surf ace analysis based on surface derivatization (with bismuth and deuteri um) prior to Temperature Programmed Desorption (TPD). These techniques are briefly described, and the rules for assigning peaks are presente d. New applications of these techniques in elucidating the mechanism a nd kinetics of the decomposition of methylcyclohexane (MCH, c-C6H11-CH 3) on Pt(111) are presented. Adsorbed MCH dehydrogenates at 230 K to f orm a pi-allyl c-C6H8-CH3,a species and three hydrogen adatoms. The pi -allyl species dehydrogenates at similar to 335 K (similar to 270 K on defects) to an adsorbed benzyl species (c-C6H5-CH2,a) and H-2,H-gas. This benzyl species dehydrogenates further at similar to 480 K (simila r to 405 K at defects) to form a species of stoichiometry C7H3,a, alth ough at defects it also produces some adsorbed benzene. This benzene d ehydrogenates at similar to 500 K. The activation energies and prefact ors for all of these processes are determined by fitting coverage vers us flash temperature curves.