ADSORPTION OF C-1-C-3 ALKANES AND C-2-C-3 ALKENES ON PT AS STUDIED BYWORK FUNCTION CHANGES AND AUGER-ELECTRON SPECTROSCOPY

The pressure and temperature dependence of the adsorption of methane, ethane, propane, ethene and propene on a Pt ribbon have been character ised by work function changes \Delta phi\ and the carbon to platinum r atio (C/Pt), determined from C/Pt AES peak intensity. C/Pt increases w ere accompanied by an increase of \Delta phi\ up to a certain value on ly. Carbon uptake was not followed by increase of \Delta phi\, i.e. of surface coverage above this value, thereby indicating the formation o f three-dimensional carbonaceous deposits. The calculated maximum cove rages were substantially lower than 1, indicating the presence of cons tant number of noncovered platinum surface sites despite increasing am ount of carbon uptake. The maximum surface coverages were nearly the s ame for methane, ethane and propane. With regard to the dipole moments of adspecies, formed at adsorption of ethane and propane these were e qual and significantly higher than those of adspecies formed upon meth ane adsorption. (C) 1998 Elsevier Science B.V. All rights reserved.